Transcript How did Earth’s Atmosphere form?

How did EartH’s
Atmosphere form?
Breathe!
No one knows of any other
planet where you can do
this simple thing.
Other planets and moons in our solar system
have atmospheres, but none of them could
support life as we know it.
So how did our atmosphere get to be so special?
Some scientists describe three stages in the
evolution of Earth’s atmosphere as it is
today.
1) Earth’s Original Atmosphere
2) Young Earth
3) Current Earth
Earth’s Original Atmosphere
•Was probably just hydrogen and helium (because these
were the main gases in the dusty, gassy disk around the
Sun from which the planets formed.)
•The Earth and its atmosphere were very hot and the
molecules of hydrogen and helium move really fast.
•They moved so fast they eventually all escaped Earth's
gravity and drifted off into space.
Young Earth
•Earth’s “second atmosphere” came from Earth itself.
There were lots of volcanoes, many more than today,
because Earth’s crust was still forming. The volcanoes
released gases like water as steam, carbon dioxide, and
ammonia.
•Carbon dioxide dissolved in seawater.
Current Earth
•Eventually, a simple form of bacteria developed that
could live on energy from the Sun and carbon dioxide in
the water, producing oxygen as a waste product.
Oxygen began to build up in the
atmosphere, while the carbon dioxide levels
continued to drop.
•Meanwhile, the ammonia molecules in the atmosphere
were broken apart by sunlight, leaving nitrogen and
hydrogen.
•The hydrogen, being the lightest element, rose to the
top of the atmosphere and much of it eventually drifted
off into space.
Now we have Earth’s “third atmosphere,”
the one we all know and love—an
atmosphere containing enough oxygen for
animals, including ourselves, to evolve.
So plants and some
bacteria use carbon
dioxide and give off
oxygen, and
animals use oxygen
and give off carbondioxide—how
convenient!
The atmosphere upon
which life depends
was created by life
itself.
• http://www.youtube.com/watch?v=uZ0wm
UDnUF4&safe=active