7.3 & 7.4 The Earth's Atmosphere In The Past/Life On Earth

Question 1

What was the earth covered in in its first billion years?

Answer 1

Volcanoes

Question 2

Name 3 things that volcanoes release

Answer 2

• carbon dioxide
• water vapour
• nitrogen

Question 3

How were the oceans formed?

Answer 3

As the earth cooled down, most of the water vapour released by volcanoes condensed to form the oceans

Question 4

What gases were in the early atmosphere?

Answer 4

• carbon dioxide

* water vapour

Question 5

What other gases did scientists believe were in the early atmosphere?

Answer 5

• nitrogen
• methane
• ammonia

Question 6

Where did most of the earths carbon dioxide, nitrogen and water vapour in the early atmosphere come from?

Answer 6

It was released by volcanoes

Question 7

What developed over the 2nd and 3rd billion years of the earth?

Answer 7

Bacteria, algae and plants

Question 8

Why did the amount of carbon dioxide in the air decrease after about 2 billion years of the earths formation?

Answer 8

It was absorbed by the plants for photosynthesis which released oxygen

Question 9

What produced the oxygen in the atmosphere?

Answer 9

Photosynthesis from the plants

Question 10

Where did the first plants probably evolve from?

Answer 10

Simple organisms like plankton and algae in ancient oceans

Question 11

Why are we not sure about how life began?

Answer 11

There are lots of theories but no proof or evidence for any of them

Question 12

How long ago do scientists believe the earth was formed?

Answer 12

4.5 billion years ago

Question 13

What was the Miller-Urey experiment?

Answer 13

An experiment based on what scientists at that time thought was in the early atmosphere

Question 14

What mixture of substances were used in the Miller-Urey experiment?

Answer 14

• water
• ammonia
• methane
• hydrogen

Question 15

What did Miller and Urey add to their experiment (not a gas) and why? What did this cause?

Answer 15

They gave the gases a high voltage spark to simulate lightning

This caused the elements to react together

Question 16

What did Miller and Urey find after a week of their experiment?

Answer 16

Amino acids had been formed

Question 17

What are amino acids?

Answer 17

The building blocks for proteins

Question 18

Name a substance that had not been made in the Miller-Urey experiment

Answer 18

•oxygen was not made

Question 19

What is the primordial soup theory?

Answer 19

The organic molecules formed a primordial soup. The amino acids in this mixture combined to make proteins from which life began

Question 20

What is the Murchinson meteorite theory?

Answer 20

Fragments of meteors contain amino acids, which shows that molecules capable of starting life may have arrived from outer space. The Murchinson meteorite landed in 1969 in Australia, weighing 100kg

Question 21

Amino acids are made from the elements carbon, hydrogen, oxygen and nitrogen. Suggest why Miller and Urey used a mixture of water, ammonia, methane and hydrogen in their experiment.

Answer 21

They all contain the elements need to make amino acids
•water contains hydrogen and oxygen
•ammonia contains nitrogen and hydrogen 
•methane contains carbon and hydrogen 
•hydrogen is hydrogen