Mixed unit, chemistry of the atmosphere ~ questions 1-10

What is the atmosphere?

A layer of gases surrounding the earth.

What was the early atmosphere composed of?

Mostly carbon dioxide.

How did the oceans form?

Water vapour condensing as the earth cooled.

How did the amount of carbon dioxide in the atmosphere decrease to today’s levels?

Dissolved in the oceans, photosynthesis, converted to fossil fuels, precipitated as metal carbonates.

When did life start to appear?

2.7 billion years ago.

What was the impact of plants on the atmosphere?

Oxygen levels increased due to photosynthesis.

How has the amount of nitrogen in the atmosphere changed over time?

It had increased.

Why can scientists no t be sure about the composition of the early atmosphere?

It was billions of years ago and the evidence is limited.

What is the current composition of the atmosphere?

Approx 80% nitrogen, 20% oxygen, and trace amounts of carob dioxide, water vapour and Nobel gases.

What is a greenhouse gas?

A gas that traps radiation from the sun.