C1.1 THE EARLY ATMOSPHERE
THE YOUNG EARTH
scientists believe that our early atmostphere was much like Titans atmosphere, 98% nitrogen. Some scientists believe this gas was released from volcanoes. There are also volcanoes on mars and venus but their atmosphere is mainly carbon dioxide. This has led other scientists to think the earths early atmosphere was mainly carbon dioxide. Scientists also believe that ammonia, methane, carbon dioxide, water vapour and nitrogen would have been present in our atmosphere.
Most scientists are certain there was little or no oxygen in the early atmosphere pn Earth. There is evidence for this idea, such as volcanoes do not give out oxygen and the Earths oldest rock compunds have no traces of oxygen. As the earth cooled down. The water vapour in the hot, atmosphere also cooled down and it is thought that this vapour condensed into liquid water and created the oceans. We have only limited evidence about the earths atmosphere when it was young. This means there are many uncertainties about these theories.
C1.2 A CHANGING ATMOSPHERE
As the earth cooled the water vapour condensed to form the oceans. Carbon dioxide then dissolved into the oceans, scientists think half of the Earth's carbon dioxide was lost in this way. Some marine organisms such as coral, molluscs and starfish- use dissolved carbon dioxide to create shells of calcium carbonate. As these creatures died their shells fell and became sediment. Over millions of years, all these layers of sediment became sedimentary rock. Limestone is mostly calcium carbonate.
Scientists believe that life on Earth started about 4 billion years ago. About 1 billion years ago some organisms developed the ability to photosynthesise, taking in carbon dioxide and releasing carbon dioxide. Over time, more photosynthesising organisms evolved, the increased the rate the carbon dioxide was removed from the atmosphere and the rate that oxygen was added.
C1.3 OXYGEN IN THE ATMOSPHERE
How much oxygen is there in the air?
Many substances, including metals, react with some metals in the air. Some metals react quickly and some react slowly. Such as iron rusts. These reactions can help us find out how my oxygen is in the air. Reactions such as these can be used to find the percentage of the oxygen in the air.
Oxygen is very important for humans. If our bodies don't get enough oxygen it can cause headaches, sickness and eventually death. However too much oxygen can be dangerous. Babies who are born prematurely have undeveloped lungs and so they struggle to breathe, doctors began to place them in incubators with high levels of oxygen but they found that some babies would go blind from having too much oxygen. Now babies are put in incubators with controlled levels of oxygen. This is another reason that it is important to be able to measure how much oxygen is in the air.
C1.4 THE ATMOSPHERE TODAY
THE COMPOSITION OF THE ATMOSPHERE
Nitrogen and oxygen make up 99% of the atmosphere. Argon, carbon dioxide, water vapour and traces of other gases make up the other 1%. Most of this other 1% are noble gases including Argon and carbon dioxide. The traces of other gases include carbon monoxide, methane, nitrogen oxide and sulfur dioxide. Amounts of these gases vary, such as volcanoes erupting can cause lots of sulfur dioxide and nitrogen oxide to be released. Other changes include, less carbon dioxide being absorbed by deforestation, burning fossil fuels releases carbon dioxide, Cattle and rice fields release methane.
FORMATION OF NITROGEN
Nitrogen today takes up 78% of the air. There are different theories of where it came from, one of these is that volcanoes released nitrogen when the earth was young.
C1.5 ROCKS AND THEIR FORMATION
Molten rock is called magma, or lava. When a volcano erupts this magma is released it then cools and becomes igneous rock. This contains crystals that interlock. For example, granite.
Rocks are broken into smaller pieces. Erosion happens when these rocks are transported- for example in a river. Once the river gets to the sea the rock settles at the bottom and becomes sedimentary rock.
The action of heat and/or pressure can change rocks causing new crystals to form. The changed rocks are called metamorphic rocks. For example marble is a metamorphic rock.
C1.6 LIMESTONE AND ITS USES
Limestone is cut into blocks to be used for constructing buildings. It is also crushed into smaller lumps and is used to make a base for railway lines. Limestone is a raw material for the manufacture of cement, glass and concrete.
Limestone is removed from the ground at a quarry. Explosives are used to break the limestone into pieces. These are cut or crushed into useful sizes.
Limestone, chalk and marble are natural sources of calcium carbonate. When its heated calcium oxide and carbon dioxide are formed.
MAKING CEMENT AND CONCRETE
cement is made by heating limestone with powdered clay. Concrete is made by mixing cement with sand, gravel and water.
C1.7 THERMAL DECOMPOSITION OF CARBON
DO ALL METAL CARBONATES BREAK DOWN IN THE SAME WAY?
Two thousand years ago, the Romans knew that calcium carbonate forms a useful product when it is heated and were using this knowledge. Archaeologists have found Roman 'lime kilns' all over Europe. These kilns were used to heat limestone to make calcium oxide which was used to make mortar and concrete
Calcium Carbonate decomposes when it is heated, producing calcium oxide and carbon dioxide. Carbon dioxide can be detected using limewater. When the carbon dioxide is passed through it the limewater turns milky.
The Pantheon in Rome was built almost two thousand years ago. its 44.3 m dome is still the largest non-reinforced concrete dome in the world.
C1.8 CHEMICAL REACTIONS
ATOMS AND CHEMICAL REACTIONS
Substances are made of atoms. An atom is the smallest part of an element that can take part in chemical reaction. A compound consits of the atoms of two or mre different elements.
In chemical reactions, the atoms of the reactions the atoms of the reactants rearrange to form new products. None of the atoms are destroyed and no new atoms are created. The new products have different physical and chemial properties.
The total mass before and after a chemical reaction is the same because things are not lost or gained only rearranged. So the mass is conserved. This works for all reactions. It is the easiest way to demonstrate in reactions where none of the reactants or products are allowed to leave the system.