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 Atmosphere2) Young Earth3) 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 carbon-dioxide—

how convenient!

The atmosphere upon which life depends was created by life

itself.

• http://www.youtube.com/watch?v=uZ0wmUDnUF4&safe=active