8.2 Earth science Flashcards
Earth’s early atmosphere
The early Earth was molten with no atmosphere until cooling allowed land masses to form. Volcanoes released gases, and Earth’s gravity trapped them, creating an atmosphere similar to Venus or Mars, mainly composed of CO₂ and water vapour, with little to no oxygen. As the planet cooled, water vapour condensed into oceans, dissolving large amounts of CO₂. This led to the formation of carbonate sediments.
How carbon dioxide decreased
Carbon dioxide decreased as it dissolved in the oceans, forming carbonate sediments. Marine organisms used carbonates to build shells and skeletons, further reducing CO₂. Green plants and algae absorbed CO₂ through photosynthesis, and when they died, their remains trapped carbon in rocks, removing it from the atmosphere.
How oxygen increased
Primitive plants and algae began photosynthesizing, using up CO₂ and releasing O₂. Algae evolved around 2.7 billion years ago, followed by small green plants. As plant life spread, oxygen levels increased, enabling more complex life forms to evolve. By 200 million years ago, the atmosphere reached its current composition of about 20% oxygen and 80% nitrogen. Marine algae contributed around 90% of atmospheric oxygen production.
Test for oxygen
The test for oxygen consists of placing a glowing splint inside a test tube of gas.
If the gas is oxygen the splint will relight.
Greenhouses gases
When shortwave radiation from the sun strikes the Earth’s surface it is absorbed and re-emitted from the surface of the Earth as infrared radiation.
Much of the radiation, however, is trapped inside the Earth’s atmosphere by greenhouse gases which can absorb and store the energy.
Carbon dioxide, methane and water vapour are gases that have this effect
Increasing levels of carbon dioxide and methane, although present in only small amounts, are causing significant upset to the Earth’s natural conditions by trapping extra heat energy.
This process is called the enhanced greenhouse effect.
Source of CO2 and methane
Carbon dioxide - Combustion of wood and fossil fuels, respiration of plants and animals, thermal decomposition of carbonate rocks and the effect of acids on carbonates.
Methane - Digestive processes of animals, decomposition of vegetation, bacterial action in swamps and in rice paddy fields.
Global warming
The level of carbon dioxide in the atmosphere has increased because we are adding more CO2 to the atmosphere and less is being removed from it. We are also adding to the amount of other greenhouse gases in the atmosphere, such as methane.
Increased levels of greenhouse gases in the atmosphere enhance the greenhouse effect as more IR radiation is absorbed and radiated back towards Earth, which causes the Earth to get warmer - this is global warming.
Increased energy consumption
Human population is increasing and with it the global demand for food, water, consumer goods, housing and energy which are supplied with greater and more widespread industrialisation.
This creates more waste so more landfill sites are needed which increases the amount of methane by decomposition.
The increased energy demands are met in most cases by the burning of fossil fuels which produces CO2:
Fossil fuel + oxygen → energy + H2O + CO2
Deforestation
Added to this is the effect of deforestation on the amount of CO2 as large areas of forested land are being destroyed for building and agricultural activities.
Plants and trees remove CO2 during photosynthesis:
6CO2 + 6H2O → C6H12O6 + 6O2
Hence their removal increases the amount of atmospheric CO2 as there are less plants available to remove it during photosynthesis.
Effects of global warming
Scientists agree that greenhouse gases are causing the average temperature of the Earth to increase by the enhanced greenhouse effect, which is causing global warming.
Climate change is when there is a shift in worldwide weather patterns and conditions.
Effects of global warming include difficulties in obtaining fresh drinking water, melting of the polar ice caps, flooding and flash fires, and the destruction of ecosystems.
Methane and farming
The greenhouse gas methane is also causing problems. Like carbon dioxide, the concentration of methane has also risen a lot in recent years due to increased human activity. For example, in livestock farming, cows produce large amounts of methane. Paddy fields, in which rice is grown, produce a fair bit too. So, the larger the population gets, the more we need to farm to produce food, and the more methane is produced.
Though it’s currently only present in tiny amounts in our atmosphere, the increasing concentration of methane is an issue as it’s a highly effective greenhouse gas.
Dealing with climate change
The production of greenhouse gases needs to be reduced drastically to avoid or at least slow climate change.
CO2 emissions can be reduced by using renewable energy supplies such as solar or wind energy instead of burning fossil fuels.
Awareness and being conscientious about reducing energy usage and our carbon footprint is another way to reduce emissions.
Other ways of mitigating the effects of climate change include:
Constructing flood defence systems in areas of low lying land.
Developing new farming methods to include switching to crops that are better adapted to the new climate.
Building more effective irrigation systems to ensure crops can get water during times of drought.
Evaluating evidence for global warming
Advances in science allow for accurate measurement of current CO₂ levels and global temperatures. Past climate conditions are estimated using fossil records, tree rings, and gas bubbles trapped in ice. Due to the complexity of Earth’s climate, creating a clear model linking global warming to greenhouse gases is challenging, leading to media speculation. However, surveys show that about 97% of climate scientists agree that human activity is causing climate change.
Historical data
Historical data is much less accurate due to the lack of accurate instrumentation and methods.
Fewer locations would also have been measured due to the lack of satellites and transport.
Unfortunately, historical methods, while providing at least some data, are not as precise as modern day techniques nor do they provide data which is representative on a global scale.
