Formation of Earth's Atmosphere Flashcards
All 25 cards in this deck
Approximately what percentage of today's atmosphere is nitrogen?
About 80% (approximately four-fifths).
Approximately what percentage of today's atmosphere is oxygen?
About 20% (approximately one-fifth).
Name three gases present in small proportions in today's atmosphere.
Carbon dioxide, water vapour and noble gases.
For roughly how long have the proportions of gases in the atmosphere been much the same as today?
For about 200 million years.
True or false? Oxygen is the most abundant gas in today's atmosphere.
False. Nitrogen is the most abundant, at about 80%; oxygen is about 20%.
What are the steps to work out the percentage of a gas in a sample of air?
e.g. 50 cm of a 250 cm air sample is oxygen- Divide the volume of the gas by the total volume:
- Multiply by 100: oxygen
According to one theory, which gas made up most of Earth's early atmosphere?
Carbon dioxide, with little or no oxygen gas.
What produced the gases that formed Earth's early atmosphere?
Intense volcanic activity during the first billion years of Earth's existence.
Which two planets have atmospheres today that may be like Earth's early atmosphere?
Mars and Venus (mainly carbon dioxide).
Which two gases may have been present in small proportions in Earth's early atmosphere?
Methane and ammonia.
Where did the nitrogen in the atmosphere come from, and how did its percentage change?
It was produced by volcanoes and gradually built up in the atmosphere.
True or false? Scientists know for certain what was in Earth's early atmosphere.
False. Evidence is limited because of the 4.6 billion year time scale, so theories have changed and developed over time.
What is the word equation for photosynthesis?
carbon dioxide + water glucose + oxygen
What is the balanced symbol equation for photosynthesis?
Which organisms first produced oxygen, and roughly when?
Algae, about 2.7 billion years ago.
What happened to oxygen levels in the billion years after algae evolved?
Plants evolved and the percentage of oxygen gradually increased, until it was high enough for animals to evolve.
True or false? The oxygen in the atmosphere was released by volcanoes.
False. It was produced by algae and plants by photosynthesis.
On a graph of atmospheric gases over time, carbon dioxide falls while oxygen rises at a similar rate. What process causes this?
Photosynthesis (by algae and plants).
How did the Earth's oceans form?
Water vapour released by volcanoes condensed as the Earth cooled.
How did the formation of the oceans reduce the carbon dioxide in the atmosphere?
Carbon dioxide dissolved in the water and carbonates were precipitated, producing sediments.
Give three processes that decreased the percentage of carbon dioxide in the atmosphere.
Photosynthesis by algae and plants, formation of sedimentary rocks, and formation of fossil fuels.
How were deposits of limestone formed?
From the shells and skeletons of marine organisms, which contain carbonates and were deposited as sediments on the sea bed.
How were deposits of coal formed?
From thick deposits of dead plant material that was buried and compressed, and did not decay fully.
How were crude oil and natural gas formed?
From layers of dead plankton (marine organisms) buried in mud on the sea bed, under high pressure and temperature.
True or false? Evidence for what was in the Earth's early atmosphere is limited because of the time scale of 4.6 billion years.
True. Because so little evidence survives, theories about the early atmosphere have changed and developed over time.