How the Atmosphere Formed and Changed Flashcards

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About how old is the Earth, and how did its early atmosphere first form?

The Earth is about 4.6 billion years old. Its early atmosphere formed from gases released by volcanoes.

What were the main gases in the Earth’s early atmosphere?

It was mostly carbon dioxide, with lots of water vapour and nitrogen, and almost no oxygen.

Why do scientists think the early Earth’s atmosphere was like the atmospheres of Mars and Venus today?

Because Mars and Venus are also rocky planets with many volcanoes and thick carbon dioxide atmospheres, which is what the early Earth is thought to have had.

How did the oceans form on the early Earth?

As the Earth cooled, water vapour in the atmosphere condensed and fell as rain, which collected to form oceans.

How did the formation of oceans help to reduce the amount of carbon dioxide in the atmosphere?

Carbon dioxide dissolved in the oceans. Some of it then reacted to form carbonates, so less carbon dioxide was left in the air.

How are carbonate rocks such as limestone linked to changes in the early atmosphere?

Dissolved carbon dioxide helped form carbonates used by sea creatures to make shells. When these died, their shells formed sediments that turned into carbonate rocks like limestone, trapping carbon from the air.

How did fossil fuels like coal, oil and natural gas form and affect the atmosphere’s carbon?

They formed from dead plants and sea organisms buried and heated over millions of years. The carbon in them originally came from carbon dioxide in the atmosphere.

Why is nitrogen now the most common gas in the Earth’s atmosphere?

Volcanoes gave out nitrogen. Nitrogen is quite unreactive, so it did not get used up much in reactions and built up to become the main gas.

What are the main gases in the Earth’s atmosphere today and their approximate percentages?

About 78% nitrogen, about 21% oxygen, and about 1% other gases such as argon and carbon dioxide.

Overall, how have the levels of carbon dioxide and oxygen in the atmosphere changed from early Earth to today?

Carbon dioxide has decreased a lot from very high levels. Oxygen has increased from almost none to about 21%.

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