Transcript History of Atmosphere on Earth

Earth Science
 When Earth’s atmosphere was
formed it contained little if any
oxygen.

Life, which appeared on Earth in the form of
bacteria, or single-celled organisms, about 4
billion years ago helped to form oxygen.


The bacteria lived in the seas that covered
most of the Earth’s surface.
They took in carbon dioxide and water and
produced oxygen as a waste product.

Over time the oxygen they produced
accumulated in the atmosphere.

Some of the oxygen was converted to ozone
by the sun’s energy.

As ozone increased, it protected Earth’s
surface from too much sunlight.

This was important later for the development
of life on land.

By about 2 billion years ago oxygen
concentration in Earth’s atmosphere had
reached 1% of its current level.

This allowed more complex oxygenproducing organisms to evolve.

Blue-green algae
Evolution is the process by
which organisms change
to give rise to new
organisms over time.

By 750 million years ago, oxygen
concentration had reached about ten percent
of the current level and organisms were
many-celled.

By 500 million years ago the ozone level was
getting close to its present value.

Land plants evolved.

Plants undergoing photosynthesis caused the
amount of oxygen in the atmosphere to
increase.

Land animals evolved next about 350 million
years ago.

Both oxygen and ozone levels reached their
current levels about 300 million years ago.

By then there were many different kinds of
complex land plants and animals living on
Earth.

How did life on Earth influence the
development of the Earth’s atmosphere?

What role did ozone play in the evolution of
life on Earth?

What do you think Earth’s atmosphere would
be like today if life had not evolved on Earth?