Science Yearly 2005 - By Eugene Siu
Science Yearly 2005 Notes
Earth History
Intrusive Igneous Formations (Plutonic)
Plutonic rocks have larger grain sizes. They tend to form gabbros, diorites and granites.
Extrusive Igneous Formations (Volcanic)
Shield Volcanos
Strato Volcano
Cinder Cone
Fossils and Sedimentary Rocks
Kinds of Fossils
Law of Superposition
The youngest rock layers are found on top of older rock layers. Intrusive igneous rocks are younger than the rocks they intrude on.
The Rock Cycle
Sedimentary Rock Formation
Weathering
Erosion
Deposition
Compaction
Lithification
Uplift and Erosion
Classification of Rocks
Sedimentary
Igneous
Metamorphic
Sedimentary Rocks
Sedimentary rocks may be made of rock fragments- sediments- or by chemical reactions.
Sediment Size Chart
Boulder: 256mm+
Cobble: 64-256mm
Pebble: 4-64mm
Granite: 2-4mm
Sand: 1/16-2mm
Silt: 1/256-1/16mm
Clay: less than 1/256mm
Roundness
The more rounded the grains the longer they have travelled and/or the faster they travelled. The 3 types are: Angular, Semi- Rounded, Rounded
Waves
Frequency- the number or repetitions per unit of time of a complete waveform
Wavelength- the distance between one peak or crest of a wave of light, heat, or other energy and the next corresponding peak or crest
Speed- the rate of measure of the rate of movement
Amplitude- the maximum absolute value of a periodically varying quantity
Transverse Waves
As a transverse wave travels through the medium, the particles oscillate along a path which is at right angles to the direction of motion of the waves which include visible light waves, radio waves and X-ray waves. Water waves approximate transverse waves, but the motion is more complex.
Longitudinal Waves (compression waves)
The particles of the medium oscillate in the same direction as the waves travel. Where the particles are bunched up together is called a compression. Where they are spread out is called a rarefaction.
Sound waves are a good example of longitudinal waves. When a tuning fork is made to vibrate, the prongs move back and forth. They can travel through liquids, solids or gases.
Sound
Compression waves of energy transmitted by vibrating matter. A sound is compression waves. Particles move forwards and backwards along the direction of the wave.
Wave Direction
Particle Movement
The frequency of the wave is the number of complete waves to pass a point in a single sound. It is measured in hertz (Hz). Frequency and pitch are related. High frequency waves produce high pitched sounds and vice versa.
Speed waves eventually stop and cannot be heard because they travel in 3 dimensions and energy is needed to spread out in those 3 dimensions. Eventually the energy runs out.
Light
Light is a transverse wave. It is part of the electromagnetic spectrum. Different types of electromagnetic waves have different wavelengths. Electromagnetic waves all travel at the speed of light (300 000km/s)
Light is a very small part of the electromagnetic spectrum. Its wavelength is approximately 0.000 0005m. Microwaves and radiowaves have wavelengths if 10m. Gamma rays have the shortest wavelength and carry the most energy. It can cause injury to the cells of living things. In general, waves with shorter wavelengths have more energy.
Wavelengths (from shortest to longest)
Gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radiowaves
Properties of Light
Absorption- When light hits an object, like soot, most of the light is absorbed so it looks black. When light hits a white object, most of the light is bounced back and the object looks bright.
Reflection- A handball bounced to another player bounces up at the same angle as the angle which it hit the ground. Light waves bounce in the same way.
Refraction- When you look at a ruler in a beaker, it looks twisted and doesn’t line up properly with the ruler out of the water. This is refraction. Your line of sight is bent by the glass and the water.
Reflection
The laws of reflection are:
A plane mirror gives an image as far behind the mirror as the object is in front. The image is also laterally inverted and virtual.
Regular reflection occurs with a smooth, shiny surface. It produces a clear image. Irregular reflection occurs with a rough surface where no clear image is produced.
Real images are those that can be projected on a screen. Although virtual images can be seen by the eye, these images cannot be focused on a screen.
Focus- the point where the rays of light meet when they are reflected
Concave mirror- telescopes, shaving mirrors
Convex mirror- rear-vision mirror
Scattering
Light waves bounce off and around as it travels so that it may reach your eyes from different angles. This process is called scattering. For example, the sky past the moon is space which is black but during the day, the sky is blue and in the evening it is red or yellow. White light is made of all the colours of the rainbow. When the light comes in straight down the atmosphere is thin and only a small amount gets scattered so the sky is blue, at sunset, the light has to travel further through the atmosphere and the blue light is scattered out so we don’t see it. We only see the reds and oranges which get through.
Refraction
Light waves travel at different speeds through different materials similar to how water waves travel in water. Notice how waves bend as they come into shore. This is because waves slow down as they reach shallow water while the waves in deep water are still travelling fast. As the light changes mediums through which it is travelling part of the wave will bend especially if it hits on an angle. The light on the inside hits first will slow down. When it changes on the other side, the bit that hits first speeds up.
Laws of Refraction
In Sickness and in Health
Microbes
Viruses
These are the smallest microbes. They cannot be classified as cells because they do not have any cell structure. They cannot carry out any life processes. These characteristics make them appear non-living but if they are inside living cells they can replicate or reproduce themselves. There are many more viruses with many different shapes. They are a protein coat that holds the genetic material (strands of DNA). It is the protein coat, called a capsid, which determines the virus’s shape. They vary in shape from 1/100 000mm to 1/2000mm. Viruses cause the common cold as well as many serious diseases like polio, small pox, hepatitis and AIDS. When a virus comes into contact with a cell, it uses the cell like a factory, causing it to make more viruses.
Bacteria
Tiny, single-celled organisms that is very simple with few structures. Some are harmful and can cause disease while others are helpful. Bacteria have a cell wall and a cell membrane but no nucleus. The rigid cell wall on the outside may also be surrounded by a slimy capsule. The membrane surrounds the cell contents, including the genetic material. Some bacteria have pili or hairs and other s may have a long whip-like structure called a flagellum, which helps them to move. Some bacteria live as single cells while others cab live together in groups of 2 or 4. Some can form long chains and others can form grape-like branches called clusters. The size of bacteria vary from 1/10 000mm to 1/20mm. Bacteria reproduce by a process called binary fission. They simply divide into 2 identical cells. If conditions are ideal, bacteria can divide every 20mins to produce huge number sin a short time. Before division can take place, a bacterial cell must grow to twice it normal size and make enough genetic material for each new cell.
Protozoa
Protozoa are single-celled organisms that have a variety of shapes. These microbes have cell membranes that surround the cell’s contents or cytoplasm. The genetic material in these organisms is contained in a nucleus. Protozoa vary in size from 1/10mm to 2mm. Most protozoa are harmless but some cause serious diseases like malaria. Protozoa divide by binary fission.
Fungi
Most fungi are multi-cellular organisms, e.g. mushrooms. Their cells are surrounded by a cell wall. However, there are also single-celled fungi such as yeast. Fungi absorb nutrients from their surroundings by feeding in dead organisms or other non-living matter. They release digestive juices outside their cells to digest food. The chemicals they release break down the organic matter into simple substances that the fungi use as nutrients. Multi-cellular fungi have thread-like filaments called hyphae from which they absorb their food. Fungi also vary in size from 1/200mm to about 50cm. Some of the microscopic fungi can infect humans and cause diseases like thrush, ringworm and athlete’s foot.
Transmission of Microbes
Air:
Contact:
Food:
Water:
Wounds:
Vectors:
Infectious and Non-Infectious Diseases
Disease
Infection
Non-Infectious Disease
First Line of Defence
Skin:
Mucous Membranes:
Cancer
Cancer is a group of disease that result from uncontrolled cell division. This is called a tumour. An oncogene is a gene that causes cancer. A carcinogen is a chemical that causes cancers. Malignant grows into surrounding tissues and benign do not.
Chemistry
Structure of the Atom
Nucleus, Quarks, Proton, Electrons, Neutrons, Shells, Orbitals
Electrons have a negative charge
Protons have a positive charge
Neutrons have no charge
Protons and neutrons carry almost all of the weight of the atom. Electrons have 1/1840 of the mass of a proton.
Atomic mass is the average atomic weight of all the isotopes.
What makes elements different from each other?
The number of protons is what differentiates elements from each other. The number of electrons equals the number of protons. The number of neutrons can vary a little allowing for isotopes. Elements that have the same number of protons but different number of neutrons, e.g. Carbon 12- 6 protons, 6 neutrons and Carbon 14- 6 protons and 8 neutrons.
If an atom loses one or more electrons, it becomes positively charged- Cation. It becomes positive because it loses negatively charged electrons. An anion will be formed if an atom gains one or more electrons. It will become negatively charged because it gains more electrons. The difference between an atom and a molecule is that a molecule if formed when 2 or more atoms join. If the atoms of a molecule are the same, then it is an element.
First 20 Elements
Valency- electrons available to donate or accept, e.g. Li+1, Be+2, C+-4, N-3, O-2, F-1, Ne
Isotope- an element that has different number of neutrons than its stable form, they can be added or removed naturally or artificially.
Radical- A group of elements that stick together in an element. The radical is always mentioned second, after the metallic element, e.g. sodium chloride.
Ions- Charged particles that have a different number of electrons than normal. A positively charged ion is called an anion and a negatively charged one is called a cation.
Naming Chemical Compounds
Two elements compounds- metal and non-metal
For example:
KBr = potassium bromide
MgO = magnesium Oxide
AlCl3 = aluminium chloride
Rules for naming a compound containing a radical
For example:
MgNO3 = magnesium nitrate
Ca(HSO4)2 = calcium hydrate sulfate
Rules for naming compounds containing no metallic elements
Electrolytes
Electrolytes are basically ions. When a substance dissolves in water it dissociates to form the ions which are free to roam around in the solution. They can be negatively or positively charged.
For example, when normal table salt (NaCl) is stirred into a cup of water it dissolves and forms stable ions. These are:
The main electrolytes in your body are:
Valency refers to the bonding power of an element or radical (PO4 or OH). Can be determined from periodic table charge refers to the difference between protons and electrons in an ion (after it dissociates).
They have a number of uses both in the body and out of the body. The most important is that by having an electric charge they can allow a current to pass through a solution containing them. This is essential in the cell membrane of our bodies as they allow electrical impulses (nerve impulses and muscle contractions) to cross into other cells.
This is why it is essential to replace lost electrolytes when exercising as they are lost in sweat. Sports drinks have extra electrolytes such as sodium chloride and potassium chloride added to help replace those lost in exercise. The sugar and flavouring is added to enhance the flavour and provide extra energy.
Electrolytes also have the useful property of being able to be electrolysed to remove them from the solution. By running a current through the solution, the positive cations will precipitate out on the negative cathode and the negative anion will precipitate out on the positive anode.
Radioactivity
Marie and Pierre Curie discovered radioactive rays coming from certain elements. These elements have unstable nuclei. The radiation is given out as the element decays. The rate of radioactive decay is called its half-life (the time for half of the sample to decay to its daughter atoms), e.g. phosphorus 32 decays to stable sulphur atoms (its half-life) in approximately 14days.
3 Types of Radiation
Alpha Particles (α particle): α particle is 2 protons and 2 neutrons bound together. It is given off by an unstable nucleus and can be stopped by sheets of paper. It has a positive charge.
Beta Particles (β particle): β particle are electrons given out when a neutron decays. It is stopped by aluminium or 1cm wood and is negatively charged.
Gamma Particles (γ particle): γ radiation is very high energy electromagnetic rays. Not charged and they can travel great distances. It can be stopped by 2-3cm lead or several metres of concrete.
Background Radiation- Unavoidable radiation around you in the atmosphere and it is usually harmless.
Alpha, Beta and Gamma Decay
Alpha Decay Rules:
Beta Decay Rules:
Nuclear Reactions
Fission
When uranium is bombarded with neutrons, the neutrons make the very large uranium nuclei split into 2 smaller nuclei, with 2 or 3 more neutrons being given off. At the same time large amounts of energy were released. This splitting of atoms is called fission.
Fission reactions which give off 2 or 3 neutrons have a very special property. Each of the neutrons given off in a fission reaction can in turn strike another nucleus and be absorbed into it. This will cause another splitting which, in turn, produces 2 or 3 more neutrons and releases even more energy.
This process is known as a chain reaction. Unless the number of neutrons which are produced is controlled, this process becomes faster and faster, and in a vert short time huge amounts of energy are released because of the large amounts of atoms being split.
If there is only a small amount of uranium present, the fission process will proceed very slowly. This is because most of the neutrons produced will escape into the air or will not have the correct amount of energy to split other uranium atoms. However, if a piece of uranium is pure enough and is bigger than a certain size, called the critical size, most of the neutrons will not escape. They will go on to split other uranium atoms.
Nuclear Reactors
The purpose of a nuclear reactor is to control the chain reaction in nuclear fission to generate electricity.
Rods made mainly of uranium oxide are placed in the reactor between large blocks of graphite. The graphite is called the moderator and acts to slow down the neutrons so they can more easily split atoms. The pile of graphite blocks with uranium between them is enclosed in special concrete and steel walls. These are to protect the outside from exposure to the very dangerous and powerful radiations produced in the reactor. Control rods, which can be pulled out in and out of the pile, absorb neutrons which are released by the fission of uranium. If the control rods are pushed right in, they will absorb enough neutrons to stop the chain reaction going on in the reactor.
Not all reactors use graphite as the moderating material to slow down the neutrons. Some use heavy water.
Nuclear Waste
Mining and processing uranium ore and the subsequent use of uranium in power stations, nuclear power engines (submarines) and the nuclear weapons industry all produce radioactive waste products.
The disposal of that radioactive waste is a problem for all countries using nuclear power. Radioisotopes with short half-lives can be stored in shielded containers until they are safe, but the storage of long-living isotopes for thousands of years is a real problem. Several alternatives have been suggested and tried:
Radioisotopes
Isotopes are atoms of an element that have different numbers of neutrons in their nuclei. Some are stable and some are not. Those that are not can decay or break up giving off high energy radiations and forming different atoms. These unstable isotopes are called radioisotopes. Radioisotopes can occur naturally or made artificially made in a nuclear reactor.
The isotopes or carbon both occur naturally. Carbon-12 is a stable isotope. It is not radioactive. However, carbon-14 is formed when high energy cosmic rays hit caerbon-12 atoms. The percentage of Carbon-14 in the air is 0.000001%.
There is only one nuclear reactor in Australia in Lucas Heights, Sydney. It is used for making radioisotopes for medical use.
Treating Cancers:
A high dose of radiation, often from the cobal-60 isotope, directed at cancer cells can kill them. Unfortunately, despite the development of machines that can direct very thin beams of radiation onto cancer cells, the radiation also affects any healthy cells it passes through. Often it doesn’t kill all the cancer cells so the cancer may reappear later.
Chemotherapy:
Makes use of the fact that some parts of the body absorb some elements and others do not. The thyroid gland absorbs iodine. A person with thyroid cancer could be given an injection containing a measured does of radioactive iodine, which would be concentrated in the thyroid and hopefully kill the cancer cells there. Of course, while it is flowing through the bloodstream the isotope can kill many other cells.
Bone Scans:
Technetium-99 is absorbed by injured bones but not healthy bones. Technetium-99 injected into the bloodstream will concentrate at any bone injury and can be detected using a gamma camera.
Radioactive Tracers:
Used to study how plants absorb different chemicals, how water flows through the ground, or how and element behaves in a chemical reaction. To follow a leak in a pipe, radioisotope is added to the water and the leak pinpointed by detecting radioactivity at the surface where water leaks out of the pipe.
Detecting Flaws:
Radioisotopes are used inside a pipe or on the other side of a metal sheet. Any flaws in a welded join in a pipe or in the internal structure if a metal sheet itself can be detected if any radiation appears through the weld or on the other side of the sheet. Stress fractures in aeroplane wings are detected this way.
Astronomy
Astronomical Distances
The unit that is chosen for most distances in space is called light years. The light year is the distance that light travels in a year. Light travels at 300 000km/s. 1 light year is approx. 10 000 000 000 000 000 km.
Astronomical Unit:
Parsec:
Brightness of Stars
The apparent magnitude is a measure of the brightness of a star viewed from earth. It is a measure of the flux of the star, which is the amount of light received by the viewer.
The absolute magnitude is the apparent magnitude of the star if it was 10 parsecs away from earth. A star 10 parsecs away from earth would have the same apparent magnitude as its absolute magnitude. It is a measure of its luminosity, which is the total amount of energy radiated per second.
Absolute magnitude is more useful that apparent magnitude for comparing stars. It removes the problems associated with a star being much further away from earth, which will make it appear less bright. By removing the distance factor all stars can be compared on their actual brightness and strength of radiation.
Star Fuel and Nucleosynthesis
Stars are giant nuclear reactors. In the centre of stars, atoms are taken apart by tremendous atomic collisions that alter the atomic structure and release an enormous amount of energy. This makes stars hot and bright.
Nuclear fusion is an atomic reaction that fuels stars. In fusion, many nuclei combine together to make a larger one (which is a different element). The result of this process is the release of a lot of energy (the resultant nucleus is smaller in mass than the sum of the ones that made it; the difference in mass is converted into energy by the equation E=mc2).
Stars are powered by nuclear fusion in their cores, mostly converting hydrogen to helium.
The production of new elements via nuclear reactions is called nucleosynthesis. A star’s mass determines what other type of nucleosynthesis occurs in its core (or during explosive changes in its life cycle). Each of us is made from atoms that were produced in stars and went through a supernova.
Small stars- the smallest stars only convert hydrogen into helium
Medium-sized stars- (like our sun) late in their lives when the hydrogen becomes depleted stars like our sun can convert helium into oxygen and carbon
Massive stars- (greater than 5 times our sun’s mass) when their hydrogen becomes depleted. Light mass stars convert helium atoms into carbon and oxygen, followed by the fusion of carbon and oxygen into neon, sodium, magnesium, sulphur and silicon. Later reactions transform these elements into calcium, iron, nickel, chromium, copper and others. When theses old, large stars with depleted cores supernova, they create heavy elements (all the natural elements heavier than iron) and spew them into space, forming the basis for life.
The Colour and Temperature of Stars
Colour (K= Kelvin)
Blue: 30 000K
White: 15 000K
Yellow: 6 000K
Orange: 4 500K
Red: 3 500K
Determining a star’s temperature from its colour
Scientists use filters on their telescopes to view light from only certain wavelengths (colours). The wavelengths at which the most energy is given out will be the brightest.
Wein’s displacement law is a formula that links the wavelengths of light at which the most energy is given out are the objects temperature.
In this way a star’s surface temperature can be determined. Hot stars thus brightest at short wavelengths (blue-white stars).
Cool stars are brightest at long wavelengths (orange-red stars).
Dopplershift/Hubble’s Law
The Dopplershift is a shift in wavelength of frequency of a wave due to relative motion of the source and receiver. If the source if waves is moving towards the receiver (or vice versa) each successive wave, it is emitted a small distance closer to the receiver, the wavelengths will be closer together and the wave will be squashed (shorter wavelengths and higher frequency). Similarly, if the source of waves is moving away from the receiver each successive wavecrest is emitted a small distance further away, the wave crests will be further apart and the wave will be ‘stretched’ (longer wave lengths, lower frequency). This is the phenomenon that causes the apparent shift in pitch (from higher approaching to lower receding) as a train passes by sounding the whistle.
These Dopplershifts have been used to determine the most stars are in fact moving away from each other. The light from stars has been examined and it shows that most light is shifted towards the red end of the spectrum, hence a red shift.
It can be used to measure distance. It refers to a change in wavelength caused by relative speed. As an object producing a sound approaches an observer, the wavelength of the sound is shorter and the sound produced is perceived to have a higher frequency than when the object is moving away from the observer. This everyday phenomenon also applies to light. The Doppler Shift of an object that is receding quickly (and thus further from the Earth). Because the universe is expanding at a tremendous rate, the distant nebulae we want to observe are moving at a very high speed. The more distant a nebula is, the faster it is moving away from us. From our viewpoint it’s just as if our galaxy ware at the centre of the universe.
Transformation of Radiation into Matter after the Big Bang
One of the basic predictions of the Big Bang theory is that the universe is expanding. This expansion indicates that the universe was smaller, denser and hotter in the distant past. At various times in the universe’s history, the temperature has gone down in proportion to the universe.
Since the universe was really hot through most of its early history, there were no atoms in the early universe, only free electrons and nuclei. The cosmic microwave background photons easily scatter off of electrons. Thus photons wandered through the early universe.
Eventually, the universe cooled sufficiently that photons and electrons could combine to form neutral hydrogen. This was thought to occur roughly 3 minutes after the Big Bang when the universe was about one-eleven hundredth of its present size. At the same time helium and deuterium were being created.
Elements heavier than lithium are all synthesised in stars. During the late stages of stellar evolution, massive stars burn helium into carbon, oxygen, silicon, sulphur and iron. Elements heavier than iron are produced in two ways: in the outer envelopes of super-giant stars and in the explosion of a supernova. All carbon based life on Earth is literally composed of star dust.
The Standard Big Bang Model
There was a big bang some 15 million years ago, when the size of the universe was zero and the temperature was infinite. The universe then started expanding at near light speed. The sequence of events in this model is:
Time t = 0 (15million years ago)
Radius = ∞
Temperature T = infinite
Density = mass per volume = infinite
t = 0.01 seconds
T = 1000 000 000 000°C
Energy is mostly radiation
t = 2 seconds
T = 10 000 000 000°C
Density = 100 million kg per cubic metre
Proton-antiproton and neutron-antineutron pairs begin forming
t = 3 minutes
T = 1 000 000 000°C
Protons and neutrons begin forming hydrogen and helium
t = 20 minutes
About 25% if the protons and neutrons in the universe are now helium
T = 10 000 years
Density = 0.000 000 000 000 000 01 kg/cubic metre
Most energy is now mass, not radiation
Condensation into stars begins
t = 15 billion years (now)
T = - 270°
Density = 10^-27 kg/cubic metre
Dynamic Earth
Story of our Continents
The continents have not always been where they are now. They used to be all joined in a giant super continent called Pangaea. This continent split into 2, Laurasia and Gondwana. Gondwana broke up and the continents moved towards their present positions.
The forces that drive the movement of the continents are found within the Earth. When material is heated up it will rise up, move across whatever boundary it comes into contact with, until it cools down when it will fall back to the heat source. This process is called ‘convection’ and it happens in the asthenosphere, a partially molten region part of the mantle below the crust (100-700 km deep). The continents move around very slowly (2-20cm/year) riding or surfing on these convection currents.
The continents however, do not move smoothly, because of the asthenosphere is only partially liquid and the continents are solid. They sometimes stick against each other. When the continents get stuck the pressure builds up and eventually the continents will ‘slip’ past each other. This causes earthquakes and volcanoes. This leads to a common link between the continental plates and earthquakes and volcanic activity around the edges of plates.
Plate Boundaries
Type of Boundary
Subduction/convergent:
Collision:
Divergent:
Transform Fault:
Folding and Faulting
Folding is when land is compressed to form mountains or valleys (anticlines or synclines). The land does not break. Can occur away from earthquake zones. Faulting is when land slips past other land. The land is broken. It occurs near plate boundaries.
Types of Faulting
Transform Fault
Normal Fault
Block Faulting
Horst Fault
Reverse Fault
By Eugene Siu (thanks a heap, this guy contributed a ton!!!) Everyone rememba to thank him!!!
Earth History
Intrusive Igneous Formations (Plutonic)
Plutonic rocks have larger grain sizes. They tend to form gabbros, diorites and granites.
Extrusive Igneous Formations (Volcanic)
Shield Volcanos
- low sloping sides
- fluid, low viscosity lava
- basalts
Strato Volcano
- steep sides
- higher viscosity lava
- may be explosive
- basalts, andesites, and rhyolites
Cinder Cone
- medium-steep sides
- basalts, ash, pyroclastic debris
Fossils and Sedimentary Rocks
- fossils are the remains of ancient plants and animals
- some fossils are found whole, e.g. insects trapped in tree sap, while others are found as imprints of the animal, such as a footprint or shell impression
- fossils can tell us what the environment the animal lived in was like
- fossils are generally found in sedimentary rocks
- organisms were generally destroyed before fossilisation
- occasionally they are found in other types of rock such as marble and slate, but they are generally damaged by the heat and pressure applied to the rock during its formation
- can only be found once the surface has erode to expose the sedimentary rock or if the rock is exposed by tunnels or mining
- fossils found in rocks are animals and plants that have died at the same time as the sediment layers were being laid down
- they are the same age as the layer of rock they are found in
- most fossils are the hard parts of animals
- many organisms fail to fossilise as the conditions must be perfect; oxygen must be excluded so that decay is slowed
- underwater fossils are much easier to be formed
Kinds of Fossils
- Unaltered Soft Parts: if bacteria and mould can be prevented from decomposing the soft remains then a fossil can form that includes the soft parts of the body
- Unaltered Hard Parts: in very recent fossils, the original hard parts may still be present
- Altered Hard Parts: replacement occurs when the fossil’s hard parts, such as its skeleton, are replaced with other minerals such as pyrite
- Trace Fossils: sediment packs hard around an organism such as a shell, then the impression of the shell in the hardened sediment is called a mould
Law of Superposition
The youngest rock layers are found on top of older rock layers. Intrusive igneous rocks are younger than the rocks they intrude on.
The Rock Cycle
- Volcanic Activity
- Weathering
- Erosion
- Transportation
- Sea
- Deposition
- Sedimentary Rock
- Heat and Pressure
- Metamorphic Rock
- Molten Magma- Source of Igneous Rock
- Movement of plates causes earthquakes
- Folding and Faulting
- Uplift of Rocks
Sedimentary Rock Formation
Weathering
- Physical
- Chemical
Erosion
- transport : ice (glaciers), water (rivers as suspended load or bed load)
Deposition
- rocks come to rest of river or glacier bed, flood plain or ocean floor
Compaction
- deposition of new layers over old ones compacts older layers
Lithification
- compaction and cementation hardens sediments into rocks
Uplift and Erosion
- Rocks are folded and lifted to surface where they are subjected to new weathering and erosion.
Classification of Rocks
Sedimentary
- Clastic: Conglomerate, Breccia, Sandstone, Siltstone, Mudstone, Shale
- Chemical: Limestone, Dolostone, Evaporites
- Biologic: Coal, Chert
Igneous
- Intrusive: Gabbro, Diorite, Grandionite, Granite
- Extrusive: Basalt, Andesite, Dacite, Rhyolite
Metamorphic
- Foliated: Slate, Schist, Gneiss
- Non- Foliated: Quartzite, Marble
Sedimentary Rocks
Sedimentary rocks may be made of rock fragments- sediments- or by chemical reactions.
Sediment Size Chart
Boulder: 256mm+
Cobble: 64-256mm
Pebble: 4-64mm
Granite: 2-4mm
Sand: 1/16-2mm
Silt: 1/256-1/16mm
Clay: less than 1/256mm
Roundness
The more rounded the grains the longer they have travelled and/or the faster they travelled. The 3 types are: Angular, Semi- Rounded, Rounded
Waves
Frequency- the number or repetitions per unit of time of a complete waveform
Wavelength- the distance between one peak or crest of a wave of light, heat, or other energy and the next corresponding peak or crest
Speed- the rate of measure of the rate of movement
Amplitude- the maximum absolute value of a periodically varying quantity
Transverse Waves
As a transverse wave travels through the medium, the particles oscillate along a path which is at right angles to the direction of motion of the waves which include visible light waves, radio waves and X-ray waves. Water waves approximate transverse waves, but the motion is more complex.
Longitudinal Waves (compression waves)
The particles of the medium oscillate in the same direction as the waves travel. Where the particles are bunched up together is called a compression. Where they are spread out is called a rarefaction.
Sound waves are a good example of longitudinal waves. When a tuning fork is made to vibrate, the prongs move back and forth. They can travel through liquids, solids or gases.
Sound
Compression waves of energy transmitted by vibrating matter. A sound is compression waves. Particles move forwards and backwards along the direction of the wave.
Wave Direction
Particle Movement
The frequency of the wave is the number of complete waves to pass a point in a single sound. It is measured in hertz (Hz). Frequency and pitch are related. High frequency waves produce high pitched sounds and vice versa.
Speed waves eventually stop and cannot be heard because they travel in 3 dimensions and energy is needed to spread out in those 3 dimensions. Eventually the energy runs out.
Light
Light is a transverse wave. It is part of the electromagnetic spectrum. Different types of electromagnetic waves have different wavelengths. Electromagnetic waves all travel at the speed of light (300 000km/s)
Light is a very small part of the electromagnetic spectrum. Its wavelength is approximately 0.000 0005m. Microwaves and radiowaves have wavelengths if 10m. Gamma rays have the shortest wavelength and carry the most energy. It can cause injury to the cells of living things. In general, waves with shorter wavelengths have more energy.
Wavelengths (from shortest to longest)
Gamma rays, x-rays, ultraviolet, visible light, infrared, microwaves, radiowaves
Properties of Light
Absorption- When light hits an object, like soot, most of the light is absorbed so it looks black. When light hits a white object, most of the light is bounced back and the object looks bright.
Reflection- A handball bounced to another player bounces up at the same angle as the angle which it hit the ground. Light waves bounce in the same way.
Refraction- When you look at a ruler in a beaker, it looks twisted and doesn’t line up properly with the ruler out of the water. This is refraction. Your line of sight is bent by the glass and the water.
Reflection
The laws of reflection are:
- The angle of incidence is equal to the angle of reflection.
- The incident ray and reflected ray are in the same plane and on opposite sides of the normal.
A plane mirror gives an image as far behind the mirror as the object is in front. The image is also laterally inverted and virtual.
Regular reflection occurs with a smooth, shiny surface. It produces a clear image. Irregular reflection occurs with a rough surface where no clear image is produced.
Real images are those that can be projected on a screen. Although virtual images can be seen by the eye, these images cannot be focused on a screen.
Focus- the point where the rays of light meet when they are reflected
Concave mirror- telescopes, shaving mirrors
Convex mirror- rear-vision mirror
Scattering
Light waves bounce off and around as it travels so that it may reach your eyes from different angles. This process is called scattering. For example, the sky past the moon is space which is black but during the day, the sky is blue and in the evening it is red or yellow. White light is made of all the colours of the rainbow. When the light comes in straight down the atmosphere is thin and only a small amount gets scattered so the sky is blue, at sunset, the light has to travel further through the atmosphere and the blue light is scattered out so we don’t see it. We only see the reds and oranges which get through.
Refraction
Light waves travel at different speeds through different materials similar to how water waves travel in water. Notice how waves bend as they come into shore. This is because waves slow down as they reach shallow water while the waves in deep water are still travelling fast. As the light changes mediums through which it is travelling part of the wave will bend especially if it hits on an angle. The light on the inside hits first will slow down. When it changes on the other side, the bit that hits first speeds up.
Laws of Refraction
- Light that moves at an angle from a less dense medium to a more dense medium bends towards the normal
- Light that moves at an angle from a more dense medium to a less dense medium bends away from the normal
- Light that moves straight on from one medium to another does not bend
In Sickness and in Health
Microbes
Viruses
These are the smallest microbes. They cannot be classified as cells because they do not have any cell structure. They cannot carry out any life processes. These characteristics make them appear non-living but if they are inside living cells they can replicate or reproduce themselves. There are many more viruses with many different shapes. They are a protein coat that holds the genetic material (strands of DNA). It is the protein coat, called a capsid, which determines the virus’s shape. They vary in shape from 1/100 000mm to 1/2000mm. Viruses cause the common cold as well as many serious diseases like polio, small pox, hepatitis and AIDS. When a virus comes into contact with a cell, it uses the cell like a factory, causing it to make more viruses.
Bacteria
Tiny, single-celled organisms that is very simple with few structures. Some are harmful and can cause disease while others are helpful. Bacteria have a cell wall and a cell membrane but no nucleus. The rigid cell wall on the outside may also be surrounded by a slimy capsule. The membrane surrounds the cell contents, including the genetic material. Some bacteria have pili or hairs and other s may have a long whip-like structure called a flagellum, which helps them to move. Some bacteria live as single cells while others cab live together in groups of 2 or 4. Some can form long chains and others can form grape-like branches called clusters. The size of bacteria vary from 1/10 000mm to 1/20mm. Bacteria reproduce by a process called binary fission. They simply divide into 2 identical cells. If conditions are ideal, bacteria can divide every 20mins to produce huge number sin a short time. Before division can take place, a bacterial cell must grow to twice it normal size and make enough genetic material for each new cell.
Protozoa
Protozoa are single-celled organisms that have a variety of shapes. These microbes have cell membranes that surround the cell’s contents or cytoplasm. The genetic material in these organisms is contained in a nucleus. Protozoa vary in size from 1/10mm to 2mm. Most protozoa are harmless but some cause serious diseases like malaria. Protozoa divide by binary fission.
Fungi
Most fungi are multi-cellular organisms, e.g. mushrooms. Their cells are surrounded by a cell wall. However, there are also single-celled fungi such as yeast. Fungi absorb nutrients from their surroundings by feeding in dead organisms or other non-living matter. They release digestive juices outside their cells to digest food. The chemicals they release break down the organic matter into simple substances that the fungi use as nutrients. Multi-cellular fungi have thread-like filaments called hyphae from which they absorb their food. Fungi also vary in size from 1/200mm to about 50cm. Some of the microscopic fungi can infect humans and cause diseases like thrush, ringworm and athlete’s foot.
Transmission of Microbes
Air:
- when people cough, sneeze or breathe, millions of microbes are released into the air
- dust particles that float in the air could contain pathogens or their spores
- e.g. whooping cough, tuberculosis, colds and flu
Contact:
- some highly contagious diseases are transmitted by physical contact with the infected person, e.g. smallpox
Food:
- bacteria reproduce very quickly if they enter food
- food is easily contaminated by microbes from the air or from the water
- e.g. typhoid, food poisoning
Water:
- untreated water that is polluted with sewage is the main source
- can be drunk, or may be used to wash hands that touch food
- poor water sanitation can result in cholera, dysentery and typhoid
Wounds:
- some pathogens can enter the body through cuts in the skin, e.g. tetanus, rabies (if bitten by animal with rabies)
Vectors:
- can be animals like mosquitoes, rats, cockroaches and house flies
- can pass directly or can be a link in a chain
- e.g. malaria, bubonic plague
Infectious and Non-Infectious Diseases
Disease
- ill at ease, sick, malady
- the result of the body not working correctly due to infection or injuries
Infection
- disease resulting from an invasion by microbes or other disease producing pathogens
- e.g. bacteria- cholera, virus- chicken pox and influenza, protozoans- malaria, amoebic dysentery, fungi- athlete’s foot and ringworm
Non-Infectious Disease
- a disease that can’t be spread to other people and was not caused by a pathogen
- e.g. hereditary- down syndrome, haemophilia, nutritional- obesity, anorexia nervosa, physiological- diabetes, cancers, environmental- cancers, deafness, lead poisoning
First Line of Defence
Skin:
- hardened outer layers of cell
- antibacterial and antifungal substances produced by sweat glands and oil glands
- bacteria that live on the surface of the skin
Mucous Membranes:
- found lining the alimentary canal, respiratory tract and the urogenital tract
- they secrete mucous which traps pathogens
Cancer
Cancer is a group of disease that result from uncontrolled cell division. This is called a tumour. An oncogene is a gene that causes cancer. A carcinogen is a chemical that causes cancers. Malignant grows into surrounding tissues and benign do not.
Chemistry
Structure of the Atom
Nucleus, Quarks, Proton, Electrons, Neutrons, Shells, Orbitals
Electrons have a negative charge
Protons have a positive charge
Neutrons have no charge
Protons and neutrons carry almost all of the weight of the atom. Electrons have 1/1840 of the mass of a proton.
Atomic mass is the average atomic weight of all the isotopes.
What makes elements different from each other?
The number of protons is what differentiates elements from each other. The number of electrons equals the number of protons. The number of neutrons can vary a little allowing for isotopes. Elements that have the same number of protons but different number of neutrons, e.g. Carbon 12- 6 protons, 6 neutrons and Carbon 14- 6 protons and 8 neutrons.
If an atom loses one or more electrons, it becomes positively charged- Cation. It becomes positive because it loses negatively charged electrons. An anion will be formed if an atom gains one or more electrons. It will become negatively charged because it gains more electrons. The difference between an atom and a molecule is that a molecule if formed when 2 or more atoms join. If the atoms of a molecule are the same, then it is an element.
First 20 Elements
- hydrogen
- helium
- lithium
- beryllium
- boron
- carbon
- nitrogen
- oxygen
- fluorine
- neon
- sodium
- magnesium
- aluminium
- silicon
- phosphorus
- sulphur
- chlorine
- argon
- potassium
- calcium
Valency- electrons available to donate or accept, e.g. Li+1, Be+2, C+-4, N-3, O-2, F-1, Ne
Isotope- an element that has different number of neutrons than its stable form, they can be added or removed naturally or artificially.
Radical- A group of elements that stick together in an element. The radical is always mentioned second, after the metallic element, e.g. sodium chloride.
Ions- Charged particles that have a different number of electrons than normal. A positively charged ion is called an anion and a negatively charged one is called a cation.
Naming Chemical Compounds
Two elements compounds- metal and non-metal
- The metallic element is named first
- The name of the non-metal element is shortened
- The suffix ‘-ide’ is added to the shortened name
For example:
KBr = potassium bromide
MgO = magnesium Oxide
AlCl3 = aluminium chloride
Rules for naming a compound containing a radical
- The metallic element is named first
- The chemical radical is named second
For example:
MgNO3 = magnesium nitrate
Ca(HSO4)2 = calcium hydrate sulfate
Rules for naming compounds containing no metallic elements
- The name of the first element is given in full
- If only two elements are present, the prefixes ‘mon’, ‘di’, ‘tri’, ‘tetra’ and so on are used to indicate how many atoms of the second element are in the molecule
- If only 2 elements are present, the name of the second is shortened and the suffix ‘ide’ is used as before
- If more than 2 elements are present, the first is named, followed by the name of the radical
Electrolytes
Electrolytes are basically ions. When a substance dissolves in water it dissociates to form the ions which are free to roam around in the solution. They can be negatively or positively charged.
For example, when normal table salt (NaCl) is stirred into a cup of water it dissolves and forms stable ions. These are:
- sodium ion (Na+) cation
- chloride (Cl-) anion
The main electrolytes in your body are:
- Sodium (Na+)
- Potassium (K+)
- Chlorine (Cl-)
- Calcium (Ca 2+)
- Magnesium (Mg 2+)
- Bicarbonate (HCO 3-)
- Phosphate (PO4 2-)
- Sulphate (SO4 2-)
Valency refers to the bonding power of an element or radical (PO4 or OH). Can be determined from periodic table charge refers to the difference between protons and electrons in an ion (after it dissociates).
They have a number of uses both in the body and out of the body. The most important is that by having an electric charge they can allow a current to pass through a solution containing them. This is essential in the cell membrane of our bodies as they allow electrical impulses (nerve impulses and muscle contractions) to cross into other cells.
This is why it is essential to replace lost electrolytes when exercising as they are lost in sweat. Sports drinks have extra electrolytes such as sodium chloride and potassium chloride added to help replace those lost in exercise. The sugar and flavouring is added to enhance the flavour and provide extra energy.
Electrolytes also have the useful property of being able to be electrolysed to remove them from the solution. By running a current through the solution, the positive cations will precipitate out on the negative cathode and the negative anion will precipitate out on the positive anode.
Radioactivity
Marie and Pierre Curie discovered radioactive rays coming from certain elements. These elements have unstable nuclei. The radiation is given out as the element decays. The rate of radioactive decay is called its half-life (the time for half of the sample to decay to its daughter atoms), e.g. phosphorus 32 decays to stable sulphur atoms (its half-life) in approximately 14days.
3 Types of Radiation
Alpha Particles (α particle): α particle is 2 protons and 2 neutrons bound together. It is given off by an unstable nucleus and can be stopped by sheets of paper. It has a positive charge.
Beta Particles (β particle): β particle are electrons given out when a neutron decays. It is stopped by aluminium or 1cm wood and is negatively charged.
Gamma Particles (γ particle): γ radiation is very high energy electromagnetic rays. Not charged and they can travel great distances. It can be stopped by 2-3cm lead or several metres of concrete.
Background Radiation- Unavoidable radiation around you in the atmosphere and it is usually harmless.
Alpha, Beta and Gamma Decay
Alpha Decay Rules:
- mass number decreases by 4
- atomic number decreases by 2
- the element changes because the atomic number changes
Beta Decay Rules:
- mass number does not change
- atomic number increases by 1 (one neutron changes into one p+ and one e-. The photon remains and the electron is emitted)
- the element changes because the atomic number changes
Nuclear Reactions
Fission
When uranium is bombarded with neutrons, the neutrons make the very large uranium nuclei split into 2 smaller nuclei, with 2 or 3 more neutrons being given off. At the same time large amounts of energy were released. This splitting of atoms is called fission.
Fission reactions which give off 2 or 3 neutrons have a very special property. Each of the neutrons given off in a fission reaction can in turn strike another nucleus and be absorbed into it. This will cause another splitting which, in turn, produces 2 or 3 more neutrons and releases even more energy.
This process is known as a chain reaction. Unless the number of neutrons which are produced is controlled, this process becomes faster and faster, and in a vert short time huge amounts of energy are released because of the large amounts of atoms being split.
If there is only a small amount of uranium present, the fission process will proceed very slowly. This is because most of the neutrons produced will escape into the air or will not have the correct amount of energy to split other uranium atoms. However, if a piece of uranium is pure enough and is bigger than a certain size, called the critical size, most of the neutrons will not escape. They will go on to split other uranium atoms.
Nuclear Reactors
The purpose of a nuclear reactor is to control the chain reaction in nuclear fission to generate electricity.
Rods made mainly of uranium oxide are placed in the reactor between large blocks of graphite. The graphite is called the moderator and acts to slow down the neutrons so they can more easily split atoms. The pile of graphite blocks with uranium between them is enclosed in special concrete and steel walls. These are to protect the outside from exposure to the very dangerous and powerful radiations produced in the reactor. Control rods, which can be pulled out in and out of the pile, absorb neutrons which are released by the fission of uranium. If the control rods are pushed right in, they will absorb enough neutrons to stop the chain reaction going on in the reactor.
Not all reactors use graphite as the moderating material to slow down the neutrons. Some use heavy water.
Nuclear Waste
Mining and processing uranium ore and the subsequent use of uranium in power stations, nuclear power engines (submarines) and the nuclear weapons industry all produce radioactive waste products.
The disposal of that radioactive waste is a problem for all countries using nuclear power. Radioisotopes with short half-lives can be stored in shielded containers until they are safe, but the storage of long-living isotopes for thousands of years is a real problem. Several alternatives have been suggested and tried:
- Dumping in sea
- Storage in vaults
- Storage in mines
- Synroc
- Firing into space
- Transporting the waste
Radioisotopes
Isotopes are atoms of an element that have different numbers of neutrons in their nuclei. Some are stable and some are not. Those that are not can decay or break up giving off high energy radiations and forming different atoms. These unstable isotopes are called radioisotopes. Radioisotopes can occur naturally or made artificially made in a nuclear reactor.
The isotopes or carbon both occur naturally. Carbon-12 is a stable isotope. It is not radioactive. However, carbon-14 is formed when high energy cosmic rays hit caerbon-12 atoms. The percentage of Carbon-14 in the air is 0.000001%.
There is only one nuclear reactor in Australia in Lucas Heights, Sydney. It is used for making radioisotopes for medical use.
Treating Cancers:
A high dose of radiation, often from the cobal-60 isotope, directed at cancer cells can kill them. Unfortunately, despite the development of machines that can direct very thin beams of radiation onto cancer cells, the radiation also affects any healthy cells it passes through. Often it doesn’t kill all the cancer cells so the cancer may reappear later.
Chemotherapy:
Makes use of the fact that some parts of the body absorb some elements and others do not. The thyroid gland absorbs iodine. A person with thyroid cancer could be given an injection containing a measured does of radioactive iodine, which would be concentrated in the thyroid and hopefully kill the cancer cells there. Of course, while it is flowing through the bloodstream the isotope can kill many other cells.
Bone Scans:
Technetium-99 is absorbed by injured bones but not healthy bones. Technetium-99 injected into the bloodstream will concentrate at any bone injury and can be detected using a gamma camera.
Radioactive Tracers:
Used to study how plants absorb different chemicals, how water flows through the ground, or how and element behaves in a chemical reaction. To follow a leak in a pipe, radioisotope is added to the water and the leak pinpointed by detecting radioactivity at the surface where water leaks out of the pipe.
Detecting Flaws:
Radioisotopes are used inside a pipe or on the other side of a metal sheet. Any flaws in a welded join in a pipe or in the internal structure if a metal sheet itself can be detected if any radiation appears through the weld or on the other side of the sheet. Stress fractures in aeroplane wings are detected this way.
Astronomy
Astronomical Distances
The unit that is chosen for most distances in space is called light years. The light year is the distance that light travels in a year. Light travels at 300 000km/s. 1 light year is approx. 10 000 000 000 000 000 km.
Astronomical Unit:
- the average distance between the earth and the sun (approx. 150 000 000km)
Parsec:
- the distance at which the baseline of length 1au subtends an angle of 1 second (one-sixtieth of a degree)
- one parsec is about 30 857 200 000 000 km
Brightness of Stars
The apparent magnitude is a measure of the brightness of a star viewed from earth. It is a measure of the flux of the star, which is the amount of light received by the viewer.
The absolute magnitude is the apparent magnitude of the star if it was 10 parsecs away from earth. A star 10 parsecs away from earth would have the same apparent magnitude as its absolute magnitude. It is a measure of its luminosity, which is the total amount of energy radiated per second.
Absolute magnitude is more useful that apparent magnitude for comparing stars. It removes the problems associated with a star being much further away from earth, which will make it appear less bright. By removing the distance factor all stars can be compared on their actual brightness and strength of radiation.
Star Fuel and Nucleosynthesis
Stars are giant nuclear reactors. In the centre of stars, atoms are taken apart by tremendous atomic collisions that alter the atomic structure and release an enormous amount of energy. This makes stars hot and bright.
Nuclear fusion is an atomic reaction that fuels stars. In fusion, many nuclei combine together to make a larger one (which is a different element). The result of this process is the release of a lot of energy (the resultant nucleus is smaller in mass than the sum of the ones that made it; the difference in mass is converted into energy by the equation E=mc2).
Stars are powered by nuclear fusion in their cores, mostly converting hydrogen to helium.
The production of new elements via nuclear reactions is called nucleosynthesis. A star’s mass determines what other type of nucleosynthesis occurs in its core (or during explosive changes in its life cycle). Each of us is made from atoms that were produced in stars and went through a supernova.
Small stars- the smallest stars only convert hydrogen into helium
Medium-sized stars- (like our sun) late in their lives when the hydrogen becomes depleted stars like our sun can convert helium into oxygen and carbon
Massive stars- (greater than 5 times our sun’s mass) when their hydrogen becomes depleted. Light mass stars convert helium atoms into carbon and oxygen, followed by the fusion of carbon and oxygen into neon, sodium, magnesium, sulphur and silicon. Later reactions transform these elements into calcium, iron, nickel, chromium, copper and others. When theses old, large stars with depleted cores supernova, they create heavy elements (all the natural elements heavier than iron) and spew them into space, forming the basis for life.
The Colour and Temperature of Stars
Colour (K= Kelvin)
Blue: 30 000K
White: 15 000K
Yellow: 6 000K
Orange: 4 500K
Red: 3 500K
Determining a star’s temperature from its colour
Scientists use filters on their telescopes to view light from only certain wavelengths (colours). The wavelengths at which the most energy is given out will be the brightest.
Wein’s displacement law is a formula that links the wavelengths of light at which the most energy is given out are the objects temperature.
In this way a star’s surface temperature can be determined. Hot stars thus brightest at short wavelengths (blue-white stars).
Cool stars are brightest at long wavelengths (orange-red stars).
Dopplershift/Hubble’s Law
The Dopplershift is a shift in wavelength of frequency of a wave due to relative motion of the source and receiver. If the source if waves is moving towards the receiver (or vice versa) each successive wave, it is emitted a small distance closer to the receiver, the wavelengths will be closer together and the wave will be squashed (shorter wavelengths and higher frequency). Similarly, if the source of waves is moving away from the receiver each successive wavecrest is emitted a small distance further away, the wave crests will be further apart and the wave will be ‘stretched’ (longer wave lengths, lower frequency). This is the phenomenon that causes the apparent shift in pitch (from higher approaching to lower receding) as a train passes by sounding the whistle.
These Dopplershifts have been used to determine the most stars are in fact moving away from each other. The light from stars has been examined and it shows that most light is shifted towards the red end of the spectrum, hence a red shift.
It can be used to measure distance. It refers to a change in wavelength caused by relative speed. As an object producing a sound approaches an observer, the wavelength of the sound is shorter and the sound produced is perceived to have a higher frequency than when the object is moving away from the observer. This everyday phenomenon also applies to light. The Doppler Shift of an object that is receding quickly (and thus further from the Earth). Because the universe is expanding at a tremendous rate, the distant nebulae we want to observe are moving at a very high speed. The more distant a nebula is, the faster it is moving away from us. From our viewpoint it’s just as if our galaxy ware at the centre of the universe.
Transformation of Radiation into Matter after the Big Bang
One of the basic predictions of the Big Bang theory is that the universe is expanding. This expansion indicates that the universe was smaller, denser and hotter in the distant past. At various times in the universe’s history, the temperature has gone down in proportion to the universe.
Since the universe was really hot through most of its early history, there were no atoms in the early universe, only free electrons and nuclei. The cosmic microwave background photons easily scatter off of electrons. Thus photons wandered through the early universe.
Eventually, the universe cooled sufficiently that photons and electrons could combine to form neutral hydrogen. This was thought to occur roughly 3 minutes after the Big Bang when the universe was about one-eleven hundredth of its present size. At the same time helium and deuterium were being created.
Elements heavier than lithium are all synthesised in stars. During the late stages of stellar evolution, massive stars burn helium into carbon, oxygen, silicon, sulphur and iron. Elements heavier than iron are produced in two ways: in the outer envelopes of super-giant stars and in the explosion of a supernova. All carbon based life on Earth is literally composed of star dust.
The Standard Big Bang Model
There was a big bang some 15 million years ago, when the size of the universe was zero and the temperature was infinite. The universe then started expanding at near light speed. The sequence of events in this model is:
Time t = 0 (15million years ago)
Radius = ∞
Temperature T = infinite
Density = mass per volume = infinite
t = 0.01 seconds
T = 1000 000 000 000°C
Energy is mostly radiation
t = 2 seconds
T = 10 000 000 000°C
Density = 100 million kg per cubic metre
Proton-antiproton and neutron-antineutron pairs begin forming
t = 3 minutes
T = 1 000 000 000°C
Protons and neutrons begin forming hydrogen and helium
t = 20 minutes
About 25% if the protons and neutrons in the universe are now helium
T = 10 000 years
Density = 0.000 000 000 000 000 01 kg/cubic metre
Most energy is now mass, not radiation
Condensation into stars begins
t = 15 billion years (now)
T = - 270°
Density = 10^-27 kg/cubic metre
Dynamic Earth
Story of our Continents
The continents have not always been where they are now. They used to be all joined in a giant super continent called Pangaea. This continent split into 2, Laurasia and Gondwana. Gondwana broke up and the continents moved towards their present positions.
The forces that drive the movement of the continents are found within the Earth. When material is heated up it will rise up, move across whatever boundary it comes into contact with, until it cools down when it will fall back to the heat source. This process is called ‘convection’ and it happens in the asthenosphere, a partially molten region part of the mantle below the crust (100-700 km deep). The continents move around very slowly (2-20cm/year) riding or surfing on these convection currents.
The continents however, do not move smoothly, because of the asthenosphere is only partially liquid and the continents are solid. They sometimes stick against each other. When the continents get stuck the pressure builds up and eventually the continents will ‘slip’ past each other. This causes earthquakes and volcanoes. This leads to a common link between the continental plates and earthquakes and volcanic activity around the edges of plates.
Plate Boundaries
Type of Boundary
Subduction/convergent:
- occur when a thinner oceanic plate collides with a thicker continental plate
- located between South American Plate and Nazca Plate
- causes both volcanoes and earthquakes
Collision:
- two continental plates colliding
- between Australian Plate and Eurasian Plate
- causes both volcanoes and earthquakes
Divergent:
- two plates move away from each other
- between South American and African Plates
- causes volcanoes
Transform Fault:
- two plates slide past each other
- Pacific plate moving past North American Plate
- Causes earthquakes
Folding and Faulting
Folding is when land is compressed to form mountains or valleys (anticlines or synclines). The land does not break. Can occur away from earthquake zones. Faulting is when land slips past other land. The land is broken. It occurs near plate boundaries.
Types of Faulting
Transform Fault
Normal Fault
Block Faulting
Horst Fault
Reverse Fault
By Eugene Siu (thanks a heap, this guy contributed a ton!!!) Everyone rememba to thank him!!!
posted by Niru at
2:25 AM
2 Comments:
Ummm....who is Dewwy Peterson - and why is he so interested in Rashies??
By
James, at 12:21 AM
woah.
eugene is such a nerd =)
anyway.
thanks for the site.
it's really good =)
saves me from writing notes..lol (:
By
Unknown, at 12:52 PM
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