Transcript The early atmosphere powerpoint File

The
Early
Atmosphere
Where did our atmosphere come from?
Earth was formed around 4600 million years ago. We don’t
know exactly, but the atmosphere was probably made up of
hydrogen and helium. The Earth was a ball of molten rock. This
probably caused the atmosphere to boil away into space.
The Earth was so hot that it probably remained molten for
millions of years. Gradually, as it cooled, a solid crust formed.
Molten rock often burst through this thin crust. Volcanoes
were now erupting all over the Earth’s surface. They poured
out lava and a mixture of gases – just as they do now. These
gases formed the Earth’s atmosphere. The gases included
ammonia (NH3), carbon dioxide (CO2), methane (CH4) and
steam (H2O).
The atmosphere – around 4000 million years ago:
The atmosphere – around 4000 million years ago:
• mainly carbon dioxide
• mainly carbon dioxide
• lots of water vapour
• lots
of water
vapour
• small
amounts
of methane, nitrogen and ammonia.
Questions:
• small amounts of methane, nitrogen and
1.ammonia.
Give two differences between the Earth’s early atmosphere and the
atmosphere we have today.
Questions:
1. Give two differences between the Earth’s early
atmosphere and the atmosphere we have today.
2. Explain why animals would not be able to survive
in the Earth’s early atmosphere.
The Earth continued to cool. As it did so, the water
vapour condensed and fell as rain. Hollows in the
Earth’s crust filled up with this rainwater – these
became our oceans.
Around 3000 million years ago, probably in the new
oceans, the first living organisms evolved. These
continued to evolve into simple plants like algae. The
algae used up carbon dioxide in a process called
photosynthesis and produced the Earth’s first
polluting gas – OXYGEN.
Gradually, the Earth’s atmosphere changed until
about 200 million years ago the atmosphere reached
the mixture we have today.
3. From where did the early atmosphere originate?
4. What were the main components of the original atmosphere?
5. What other substances were found in the atmosphere?
6. Name the Earth’s first ‘polluting’ gas.
7. What produced this polluting gas?
8. Explain why this gas is classed as being ‘polluting’.
What changes have taken place?
The carbon dioxide level has decreased dramatically.
How?
The carbon dioxide dissolved in the new oceans. It then
concentrated into the shells of sea creatures as the compound
calcium carbonate. Eventually these shells have become
compacted together over millions of years to form limestone – a
sedimentary rock.
The oxygen level has slowly increased.
How?
As more and more plants evolved, the process of photosynthesis
increased. The plants use up carbon dioxide and produce oxygen.
9. Name the gas in the atmosphere that has seen the biggest
(and quickest) change over time.
10. Explain how this change came about.
11. Name the gas in the atmosphere that has slowly increased
over time.
12. Explain how this change came about.
Ozone
Some of this new oxygen turned into ozone (O3). This
gas is found in the ‘ozone layer’ between around 15000
and 40000 km above sea level.
Ozone is important since it filters out harmful ultraviolet
radiation from the sun. Ultraviolet radiation can cause
some skin cancers and cause cataracts to form in the
eyes.