The Evolution of the Atmosphere

Question 1

For how long has the present-day atmosphere been the norm on Earth?

Answer 1

Around 200 million years

Question 2

What is our atmosphere mainly comprised of today?

Answer 2

1. 78% nitrogen
2. 21% oxygen
3. Small amounts of other gases, mainly carbon dioxide, noble gases, and water vapour

Question 3

Phase 1

Describe the landscape of the earth 4.5 billion years ago

Answer 3

Molten - so hot that any atmosphere just ‘boiled away’ into space.

Eventually it cooled down a bit, and a thin crust formed, but volcanoes kept erupting.

The volcanoes gave out lots of gas.

Oceans formed when water vapour condensed

Question 4

Phase 1

How do we think the oceans and atmosphere were formed?

Answer 4

From the gas given off by volcanoes

Question 5

Phase 1

Describe the early atmosphere

(3)

Answer 5

1. Mostly CO₂
2. Virtually no oxygen
3. Maybe water vapour, methane, and ammonia

Question 6

Phase 1

What was the Earth’s early atmosphere probably similar to?

Answer 6

The atmospheres of Mars and Venus today

Question 7

Phase 2

What 2 organisms evolved on the Earth?

Why?

Answer 7

1. Green plants
2. Algae

They could live in an atmosphere that was mostly CO₂

Question 8

Phase 2

What changes happened to the atmosphere in phase 2?

Answer 8

Became less abundant in CO₂, and more abundant in oxygen

Question 9

What 2 things caused the changes in the Earth’s atmosphere in phase 2?

Answer 9

1. A lot of the early CO₂ dissolved into the oceans
2. The green plants and algae absorbed some of the CO₂ and produced oxygen by photosynthesis

Question 10

What happened to the early plants and algaes, along with the skeletons and shells of early marine organisms when they died?

(2 parts)

Answer 10

1. They were buried under layers of sediment.
2. The carbon and hydrocarbons inside them became ‘locked up’ in sedimentary rocks as insoluble carbonates (e.g. limestone) and fossil fuels

Question 11

What happens when we burn fossil fuels today?

Answer 11

The ‘locked up’ carbon inside them is released and the concentration of CO₂ in the atmosphere increases

Question 12

What 3 things did the build of oxygen in the atmosphere do?

Answer 12

1. Killed off some early organisms that couldn’t tolerate it
2. Allowed other more complex organisms to evolve and thrive
3. Created the ozone layer (O₃), blocking harmful rays from the Sun and enabling more complex organisms to evolve

Question 13

How much CO₂ is left in the atmosphere now?

Answer 13

Virtually none