C1.7 Changes In The Earth And Its Atmosphere

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GCSE Chemistry (C1) Mind Map on C1.7 Changes In The Earth And Its Atmosphere, created by killthemoment on 07/24/2014.

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C1.7 Changes In The Earth And Its Atmosphere
1 C1.7.1 The Earth's Crust
1.1 The Earth’s crust, its atmosphere and oceans are the only sources of the resources that humans need.
1.1.1 The Earth has a layered structure, including the core (made from liquid nickel and iron), mantle (has the properties of a solid, but can flow very slowly - magma) and crust (relatively thin and rocky). The radius of the core is just over half the radius of the Earth. The core itself consists of a solid inner core and a liquid outer core. The crust and upper mantle are cracked into large pieces called tectonic plates. These plates move slowly, but can cause earthquakes and volcanoes where they meet. The plates are constantly moving due to convection currents in the magma, which are driven by the heat produced by the natural decay of radioactive elements in the Earth. This process is called continental drift. Where tectonic plates meet, the Earth's crust becomes unstable as the plates push against each other, or ride under or over each other. Earthquakes and volcanic eruptions happen at the boundaries between plates, and the crust may ‘crumple’ to form mountain ranges. It is difficult to predict exactly when an earthquake or volcanic eruption might happen because we cannot observe this phenomenon. We simply don't have the equipment to measure the stresses on the rocks bordering the faults, to see the underlying movement of the more plastic rocks of the mantle that lie 50-160 km below the surface, and to know how much longer the rocks can withstand the strain before they crumble under the pressure. The theory of plate tectonics and continental drift was proposed by Alfred Wegener. Wegener’s theory suggested that mountains were formed when the edge of a drifting continent collided with another, causing it to crumple and fold. It took more than 50 years for his theory to be accepted because it was difficult to work out how whole continents could move: it was not until the 1960s that enough evidence was discovered to support the theory fully.
2 C1.7.2 The Earth's Atmosphere
2.1 Air is a mixture of gases with different boiling points and can be fractionally distilled to provide a source of raw materials used in a variety of industrial processes.
2.1.1 For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today: 80% nitrogen, 20% oxygen and small proportions of various other gases, including carbon dioxide, water vapour and noble gases. During the first billion years of the Earth's existence there was intense volcanic activity which released the gases that formed the early atmosphere and water vapour that condensed to form the oceans. There are several theories about how the atmosphere was formed, which was probably mostly carbon dioxide with little or no oxygen. There were smaller proportions of water vapour, ammonia and methane. It is thought that the atmospheres of Mars and Venus today are similar to the early atmosphere of the Earth. There is evidence that the first living things appeared on Earth billions of years ago. There are many scientific theories to explain how life began. One theory involves the interaction between hydrocarbons, ammonia and lightning. Stanley Miller and Harold Urey carried out experiments see if substances now made by living things could be formed in the conditions thought to have existed on the early Earth. They sealed a mixture of water, ammonia, methane and hydrogen in a sterile flask, which was heated to produce water vapour. Electric sparks were passed through the mixture of water vapour and gases, simulating lightning. After a week, contents were analysed. Amino acids, the building blocks for proteins, were found. The Miller-Urey experiment supported the theory of a ‘primordial soup’, the idea that complex chemicals needed for living things to develop could be produced naturally on the early Earth. Plants and algae photosynthesised; increasing oxygen and decreasing carbon dioxide in the atmosphere. The decrease of carbon dioxide in the atmosphere was not just because of photosynthesis; most of the carbon gradually became locked up in sedimentary rocks as carbonates and fossil fuels and carbon dioxide dissolved in the oceans. Limestone was formed from the shells and skeletons of marine organisms. Fossil fuels contain carbon and hydrocarbons. The oceans act as a reservoir for carbon dioxide but increased amounts absorbed by the oceans is making it more acidic and has an impact on the marine environment; making the shells of sea creatures thinner than normal. Today, 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, contributing to global warming.
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