The Evolution of the Atmosphere - Volcanoes Gave O
Volcanoes Gave Out Gases
1) The Earth surface was originally molten for many milionf of years. It was so hot that any atmosphere just 'bolied away' into space.
2) Eventually things colled down a bit ans a thin crust formed, but volcanoes kept erupting.
3) The volcaones gave out a lots of gas - including carbon dioxide, water vapour and small amount of other gases. We think this was how the oceans and atmposohere were formed,
4) According to this theory, the early atmosphere was probably mostly Carbon dioxide, with virtually no oxygen. This is quite like the atmosphere of Mars and Venus today.
5) The oceans formed when the water vapour condenced.
The Evolution of the Atmosphere - Green plants evo
Green Plants Evolved and Produced Oxygen
1) A lot of the early carbon dioxide dissolved into the oceans.
2) Later, marine organisms developed, which took in some of this carbon dioxide. When they died the organisms were buried under layers of sedmient and the Carbon dioxied became 'locked up in cabronate rocks.
3) Green plants evolved over most of the Earth. They were quite happy in the carbon dioxide atmosphere
4) The green plants also removed carbon dioxide from the air and produced oxygen by phitisynthesis. This caused the oxygen level to gradually increase.
The Evolution of the Atmosphere - Ozone Layer allo
Ozone Layers Allows Evolution of Complex Animals.
1) The build-up of oxygen in the atmosphere killed off some early organisms that couldn't tolerate it, but allowed some, more complex organisms to evolve ans flourish.
2) The oxygen also create the ozon layer (O3) which blocked hrmful rays from the Sun and enabled even more complex organisms to evolve - us, eventauul.
3) There is very little carbon dioxide now.
Today's atmosphere - human activities.
Human activities is changing the atmosphere.
1) Burning fossil fuels release carbon dioxide - and as the world's become more industrualised, more fossil fuels have been birnt in power station and in car enginge.
2) Deforestation - also constributes to the increase in Carbon dioxide level. Trees take in carbon dioxide from the atmosphere so getting rid of a whole load means more carbon dioxide is left in the atmosphere.
3) Livestock farming realeases huge amount of methan, CH4, into the atmosphere - animals produce it when they pass wind (tee hee). The large population od dairy and beef cattle is to blame.
Volcanic avitivity is changing the atmosphere.
1) Sulfur dioxide can be thrown high up into the atmosphere when volcanoes erupt. Sulfur dioxide gas reacts with sunlight, water, oxygen asn dust from volcanic somg.
2) Carbon dioxide is also realeased into the atmosphere by volcanic eryuptions.
Sources of information on the evolution of the atmosphere are limited:
1) We;ve leraned a lot about the past atmosphere frome Antarctic ice cores. Each year, a layer of ice forms and bubbled of air get trapped inside it, then it;s burried by the next layer. So the deeper the ice, the older air - and if you examine the bubbles in differen layers, you can see how the air has changed. The measurements have to be ultra-precise though, as the changes between layers can be very tiny.
2) However, because no one was actually there at the time, it's difficult to be precise about exactly how the atmosphere has changes - some of it's down to guesswork.
You can investigation the proportion of ozygen in
You can investigation the proportion of ozygen in the Atmosphere.
Here's nice experiment that shows that the atmosphere today contains around one fifth oxygen.
1) When it's heated, copper reacxts with oxygen in the air to make copper(II) oxide - so the reaction uese up oxygen.
2.)If you heat an excess of copper in a tube and pass air over it using two syringes, you can use the markers on the syringes to tell how much oxygen has been used up.
3) So, if you start with 100 cm^3 of air, you'll end up with about 80 cm^3 when the reaction's finished and the ari has colled. If 20 cm^3 of the air has goen then around 20% of the air must to be oxygen.
Three steps in formation sedimentary rocks:
1) Sedimentary rocks are formed from layers of sediment laid down lakes or seas.
2) over millions of years the layers get buried under more layers and the weight pressing down squeezes out the water.
3) Fluids flowing through the pores deposit natural mineral cement.
Limeston and Chalk.
Limestone and chalk are sedimentary rocks and they contains fossils. The rock isn't formed at high temperature - so the remain and impronts of dead organisms aren't destroyed.
Limestone and chalk are easily breake down by wind, rain and waves - this is called erosion and it can change shape of our landscape.
Metamorphic rocks are formed from other rocks.
Metamorphic rocks are formed by the action of heat and pressure on sedimentary (or even ignous) rocks ove long period of time.
The mineral structure and texture may have changed but the chemical composition is often the same as the original rock.
So long as the rocks don't actually melt they're classed as metamoprhic. If the melt and turn ti magma, ther're gone (though they mat eventually resurface as ignose rocks)
Marble is fromed from limestone and chalk. Very high temperature break down the limestone asn it reforms as small crystals. This give marble a more even texture and make it much harder.
Ignoud rocks are foremd from fresh magma.
Igneous rocks form when molten magma pushes up into the crust (or right through it) before cooling and solidifying. They contain various different material in randomly arranged interlocking crystal.
There are two types of ignous rocks, extrusive and intrusive:
- EXTRUSIVE ignous rocks cool QUICKLY ABOVE GROUND, forming SMALL crystal, e.g. basalt.
- INTRUSIVE ignous rocks cool SLOWLY UNDERGROUND, foming BIG crystals e.g. granite.
Granite is very hard (even harder than marble) It's ideal for steps and buildings.
Limestone as Building Material
Limestone is a bit of a boring grey/white colour. It's often formed from the sea shells and although the original shells are mostly crushed, there are still quite a few fossilised shells remaining. It's quarried out of the ground. This causes some environmental problems though. It's great for making into blocks for builginds with. Fine old buildings like cathedrals are often made purely from limestone blocks. It's also used for statues and fancy carved bits on nice buildings too. Limestone's virtually insoluble in plain water. But acid rain is a big problem - the acid rectrs with the liestone asnd dissloves it away. Limestone can also be crushed up into chippings and used in raod surfacing.
Limestone is used to make othr useful things too.
Limestone is the raw matrial used to produce other building material, so it's quarried on a large scal. Powderedlimeston is heated in a klin with powdered caly to make cement. You can mix the cement with san, water and gravel to make concrete. Limestone is also used to made glass. You just heat it with sand and sodium carbonate until it melt.
Limestone and Thermal decomposition
Limestone is mainly calcium carbonate (CaCO3). When it is heated it thermally decomposes to make calciu carbonate ans carbon dioxide (CaCO3 -> CaO +CO2). Whe other carbonates are heated they decompose in the same way. Thermal Deco,position of carbonates gives off carbon dioxide. Zinc carbonate and copper carbonate decompose in the same wat as calcium carbonate. (copper: CuCO3->CuO +CO2 and zinc: ZnCO3->ZnO+CO2)(Experiment: Heat the carbonate in a boling tube ans pipe off the gas into a test tube filled with limewater -Ca(OH)2. The CO2 will turn the limewater milky). Some carbonates undergo thermal decomposition more eaily than others - it depends on the stability of the metal carbonate. Less stable carbonate will decompose fast and the limestone will turn milky quickly. Sometimes there's coulour change - e.g. copper carbonate is green and copper oxide black. Calcium oxide reacts with water to produce calcium hydroxide. When you add water to calcium oxide you get calcium hydroxide. [CaO +H20 ->Ca(OH)2] Calcium hydroxide is an alkali which can be used to neutralise acidic soil in fields. Powdered calcium oxide can be used for this too, but the advantage of calcium hydroxide is that works much faster. Calcium hydroxide dissolves in water to produce a solution known as limwater (limewater isn't actually water with limes dissolved in it. Its proper name, calcium hydroxide, is much less inspiring.
Disadvantage of quarrying limestone: 1. It makes huge ugly holes which permanently change the landscape. 2. Quarrying processes, like blasting rocks apart with explosives, make lots of noise and dust in quiet, scenic areas. 3. Quarrying destroys the habitats of animals and birds. 4. The limestone nedds to be transported away form the quarry - usually in lorries. This caused more noise and pollution. 5. Waste materials produce unsightly tips. Advantage of quarrying limestone: 1. Provides things that people needs- houses and roads. Chemical used in making dyes, paints and medicines also come from limestone. 2. Limestone products are used to neutralise acidic soil. Acidity in lake and rivers caused by acid rain is also neutralsied by limestone products. 3. Limestone is also used in power station chmneys to neutralise sulphur dioxide, which is a casue of acid rain. 4.The quarry and associated businessed provide jobs for people and bring money into local economy. This can lead to local imporvement.
Atoms and Mass in Chemical Reactions
Atoms Elements and compounds are made uo of atoms - the smallest particles you can get of each element. It's the atoms that take part in chemical reaction. During chemical reaction, things dont't appear out of nowhere ans things don't just disappear. You still have the same atoms at the end ot the reaction as you had at the start. Thery're arranged in different eays to give new products with different properties from the reactents. Balanced symbol equation show the atoms at the start (the reactanst atoms) and the atoms at the end (the product atoms) snd how they'ra arranged. Because atoms aren't gain ot lost, the mass of the reactants equals the mass of the products.
State symbols using in balanced equation:
(s) - solid
(l) - liquid
(g) - gas
(aq) - dissolved in water