C1.1

Question 1

Why do scientists think there wasn’t oxygen in the early atmosphere

Answer 1

Volcanoes don’t release it and some of the oldest rocks contain iron compounds that only form in the absence of oxygen

Question 2

Where do scientists think water came from

Answer 2

As the earth aged, it cooled and the water vapour in the atmosphere condensed

Question 3

How was sedimentary rock formed (co2)

Answer 3

Co2 dissolved into the see. See creatures such as molluscs used the co2 in the water to form calcium carbonate for their shells. When they died, the shells sunk to the bottom of the say and over time, layers of it formed sedimentary rock due to the heat and pressure

Question 4

How do scientists think oxygen got into the atmosphere

Answer 4

About 1 billion years ago, organisms began to photosynthesise so they took in the co2 and began releasing o2. Over time, these plants spread, increasing the amount of photosynthesis and increasing the amount of oxygen in the air

Question 5

What are the four main gases I the atmosphere and their percentages

Answer 5

Nitrogen, 78
Oxygen, 21
Argon, .9
Co2, .04