Chemistry - The earth Flashcards
What is the structure of the earth
crust – relatively thin and rocky
mantle – has the properties of a solid, but can flow very slowly
outer core – made from liquid nickel and iron
inner core – made from solid nickel and iron
Who came up with the theory of continental drift
The theory of continental drift was proposed at the beginning of the last century by German scientist Alfred Wegener.
What was evidence for Wegener’s theory
The match in shape between the east coast of South America and the west coast of Africa suggests both were once part of a single continent (meaning that the outlines of the continents fit together like a jigsaw).
There are similar patterns of rocks on both sides of the Atlantic.
There are similar fossils on both sides of the Atlantic – including the fossil remains of land animals that would have been unable to swim across from one side to the other.
What is the process of continental drift
The Earth’s crust and upper part of the mantle are broken into large pieces called tectonic plates. These are constantly moving at a few centimetres each year. Although this doesn’t sound like very much, over millions of years the movement allows whole continents to shift thousands of kilometres apart. This process is called continental drift.
What is a deconstructive boundary
A boundary where the plates are moving towards each other. Often, the denser of the two plates is pushed under the other plate where it moves into the mantle and melts. This creates molten rock (magma) which can then be pushed up through the plates, causing earthquakes and volcanoes. The molten rock then cools to form new igneous rock.
What is a constructive boundary
A boundary where the plates are moving away from each other. Magma from beneath the plates is released from the gap and rises up, cools and forms new igneous rock. If this happens under pressure, it is known as a volcanic eruption. An example of this boundary type is the Mid-Atlantic ridge.
What is a conservative boundary
A boundary where the plates slide past one another without moving towards or away from each other. If the plates move a significant distance very suddenly, this causes an earthquake. There are no volcanoes at this type of boundary as melting of the rock does not occur. An example of this type of boundary is the San Andreas fault, California.
How do scientists think the early atmosphere was formed?
Its early atmosphere was probably formed from the gases given out by volcanoes.
How were the oceans formed?
As the Earth cooled down, most of the water vapour condensed and formed the oceans.
What evidence do scientist have about the early atmosphere?
Volcanoes release high quantities of carbon dioxide. Iron-based compounds are present in very old rocks that could only have formed if there was little or no oxygen at the time.
How did the proportion of carbon dioxide, methane and ammonia in the atmosphere go down, and the proportion of oxygen go up?
-The proportion of oxygen increased because of photosynthesis by plants.
-The proportion of ammonia decreased as it reacted with the newly formed oxygen in the atmosphere to form nitrogen and water vapour.
-The proportion of methane decreased as it reacted with the newly formed oxygen to form carbon dioxide and water.
The proportion of carbon dioxide went down because:
-It was locked up in sedimentary rocks formed from marine animal shells (such as limestone and chalk) and in fossil fuels
-It was absorbed by plants for photosynthesis
-It dissolved in the oceans
How much of each gas is in the worlds atmosphere currently?
78% nitrogen
21% oxygen
0.9% argon
0.04% carbon dioxide
How does the percentage of carbon dioxide remain constant?
Respiration – nearly all living cells use oxygen to obtain energy from their food using respiration. This process takes in oxygen from the atmosphere and releases carbon dioxide.
Combustion – whenever organic material, such as wood or grass, burns, oxygen reacts with the carbon and hydrogen in the material, releasing heat and light in the form of fire. This process takes in oxygen from the atmosphere and releases carbon dioxide.
Photosynthesis – plants produce their own food in the form of glucose using the process of photosynthesis. This process uses sunlight (and so only occurs during the day) to remove carbon dioxide from the atmosphere and release oxygen.
What factors have contributed to the increasing carbon dioxide levels?
-The burning of fossil fuel – this process is adding carbon dioxide to the atmosphere faster than it can be removed by photosynthesis
-The growth of human and animal populations – this has increased the overall level of respiration, leading to increased carbon dioxide levels
-Deforestation – cutting down large areas of forest and rainforest for resources such as wood, so that the land can be used as farmland reduces the amount of photosynthesis occurring, and so less carbon dioxide is removed from the atmosphere
How is acid rain formed?
Many fossil fuels contain sulfur impurities. When these fuels are burned, the sulfur is oxidised to form sulfur dioxide. This sulfur dioxide then dissolves in droplets of rainwater to form sulfuric acid.
