Topic 13 - The Earth's Atmosphere Flashcards
What do scientists think about how the Earth’s early atmosphere came to be?
-Volcanoes released carbon dioxide, water vapour and nitrogen and these gases formed the early atmosphere.
-Water vapour condensed as the Earth gradually cooled down, and fell as rain.
-Water collected in hollows in the crust as the rock solidified and oceans were formed.
-A different theory suggests that comets could also have brought water to the Earth. As icy comets rained down, they melted, adding to the water supply.
What do scientists think Earth’s early atmosphere was like (after it stabilised)?
-The atmosphere was mainly carbon dioxide. There was probably also some water vapour and nitrogen gas, and traces of Methane and ammonia.
-There would have been little to no oxygen at this time.
-This resembles planets like Mars and Venus nowadays.
-After the initial violent years of the Earth’s history, the atmosphere remained quite stable until life first appeared on Earth.
How did life first form and how was oxygen released as a result?
-Scientists think life began around 3.4 billion years ago when prokaryotes like Bacteria first appeared around the ‘primordial soup’. These could use the breakdown of chemicals as a source of energy.
-About 2.7 billion years ago, bacteria and other simple organisms evolved. Algae use energy from the Sun to make food by photosynthesis, a process now used by plants. This produced oxygen gas as a waste product.
-Over the next billion years, levels of oxygen rose steadily as algae and bacteria thrived in seas. More and more plants evolved that photosynthesised, removing carbon dioxide and replacing it with oxygen in the atmosphere.
-Plants then colonised most of the surface of the Earth. This made it possible for the first animals to evolve.
How can carbon be ‘locked into’ rock?
-Carbon dioxide is taken in by plants during photosynthesis. Carbon in glucose can end up in plant material. When animals eat them, some carbon can be transferred to animal tissues like bones.
-Skeletons and shells built up at the bottom of oceans. They became covered by sediment. Eventually, deposits formed sedimentary rocks like limestone, which contains mainly calcium carbonate.
How were fossil fuels formed?
Some remains of ancient organisms were crushed by mass movement and were heated within the Earth’s crust. They formed coal, crude oil and natural gas.
How were Ammonia and Methane released into the atmosphere?
-Volcanoes produced nitrogen gas, which built up in the early atmosphere, as well as methane and ammonia. Methane and ammonia found in the early atmosphere reacted with oxygen which was formed by evolving algae and plants.
-This removed methane and ammonia from the atmosphere. Levels of nitrogen gas could build up, however, since nitrogen is very unreactive.
What is the composition of the Earth’s atmosphere today?
-For 200 million years, proportions of gases in the atmosphere have been stable.
-Around 78% of the atmosphere is nitrogen.
-Around 21% of the atmosphere is oxygen.
-Around 0.9% of the atmosphere is argon.
-Around 0.04% of the atmosphere is CO2.
-The remaining % are traces of other gases.
What are the main greenhouse gases?
Carbon dioxide, methane and water vapour.
How does the greenhouse effect work?
When radiation is received from the Sun, short wavelength electromagnetic radiation passes through the atmosphere. The Earth’s surface cools by re-emitting long wavelength radiation. However, greenhouse gases absorb this radiation. The radiation stimulates bonds in the molecules to vibrate, bend and stretch more vigorously, raising their temperature. This raise in temperature is in turn the cause for the increase in temperature in our atmosphere. The more greenhouse gases in the atmosphere, the higher the temperature raise.
How are carbon dioxide levels increased?
Fossil fuels are used to make electricity, heat homes and run cars by combustion, which releases useful energy but also releases greenhouse gases. Carbon that has been ‘locked away’ from the atmosphere for millions of years is being released again. Carbon dioxide is released in all of these processes.
How are methane levels increasing?
Methane gets into the atmosphere from swamps and rice fields, but also from the decomposing waste of grazing cattle. The increased demand for meat due to a rising population leads to more cattle being farmed, increasing the amount of methane released. Also, the more waste humans produce, the more methane is released at landfill sites.
Why can the greenhouse effect be good in certain circumstances?
The heat trapped in the atmosphere is needed for life to exist, without the greenhouse effect life on Earth, as we know it, would be impossible.
How do scientists check the carbon dioxide levels in the past?
-Ice cores can be drilled, containing a different content of gases from the time it trapped to the content of gases in our atmosphere nowadays.
-Parish records can show how climate has changed
-Tree rings can show how temperature has changed over time
What is the problem with making judgements on greenhouse gases?
Even with the aid of the most powerful computers, you cannot predict with certainty, the effects of increasing greenhouse gases.
What is the conclusion scientists have come to about greenhouse gases and climate change?
That, by various processes like combustion or farming of cattle, greenhouse have increased dramatically compared to pre-industrial revolution fluctuations, which is causing the average temperature on Earth to rapidly increase and for weather conditions to hence become more extreme.
