Earth’s Atmosphere
Past atmosphere:
early atmosphere was probably formed from the gases given out by volcanoes. It is believed that there was intense volcanic activity for the first billion years of the Earth's existence.
The early atmosphere was probably mostly carbon dioxide, with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. As the Earth cooled down, most of the water vapour condensed and formed the oceans.
Present atmosphere:
The proportion of oxygen went up because of photosynthesis by plants.
The proportion of carbon dioxide went down because:
- It was locked up in sedimentary rocks, such as limestone, and in fossil fuels.
- It was absorbed by plants for photosynthesis.
- It dissolved in the oceans.
The burning of fossil fuels is adding carbon dioxide to the atmosphere faster than it can be removed. This means that the level of carbon dioxide in the atmosphere is increasing.
Composition of the Earth's atmosphere
The Earth's atmosphere has remained much the same for the past 200 million years. The pie chart shows the proportions of the main gases in the atmosphere.
Carbon Cycle
The carbon cycle describes how carbon circulates around an ecosystem. Carbon will change form. Sometimes it is an element and sometimes a compound. Carbon is passed between living organisms and between non-living and living systems. There are many different elements to the carbon cycle.
- Producers, e.g. plants/algae use carbon dioxide and water to make energy through the photosynthesis process.
- Animals consume the producers they use the carbohydrates to provide the energy for reproduction, growth and daily living. They respire which requires oxygen and carbohydrates and produces as a by-product carbon dioxide and water. The CO2 is exhaled by animals back into the atmosphere where the carbon cycle begins again.
- When organisms die, they decompose. This releases nutrients into the soil, but carbon remains stored in the remains of the animals. It can remain stored for a very long time and can be still be used to provide energy.
- When this energy is released by humans through burning fossil fuels in industrial processes, carbon gasses, such as carbon dioxide are released into the atmosphere.
The diagram shows how carbon moves through the environment, through the processes of photosynthesis, respiration, factory emissions and other chemical and biological processes.
Tectonic Plates
The lithosphere is broken up into tectonic plates. These plates move in relation to one another. There are three types of plate boundaries, which are:
Transform boundaries: Occur where plates slide or, perhaps more accurately, grind past each other along transform faults. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer).
Divergent boundaries: Occur where two plates slide apart from each other. Mid-ocean ridges and active zones of rifting are both examples of divergent boundaries.
Convergent boundaries: Occur when two plates slide towards each other commonly forming either a sub duct ion zone (if one plate moves underneath the other) or a continental collision (if the two plates contain continental crust).
Wegner’s Idea: Continental Drift
Alfred Wegener is proposed his theory of continental drift, 1915, which hypothesized that continental drift is the movement of the Earth's continents relative to each other.
