Our Atmosphere Came From Space Gases, Study Says

The new theory came about after scientists discovered that pristine samples of the elements krypton and xenon, recently collected from deep within the Earth, have the same chemical makeup as ancient meteorites.
The discovery has squelched the volcano theory, said project leader Chris Ballentine of the U.K.'s University of Manchester.

Most of the gases in the air we breathe originated in the solar nebula, the cloud of gas and dust that formed the sun and planets, the study says.

The gases became gravitationally bound to a young Earth and were then transported in the Earth's interior—leaking out over the eons through volcanic belches and cracks in the Earth's crust.

It's still true that volcanoes spewed out some gases, "but [that] contribution was insignificant" for the creation of Earth's atmosphere," Ballentine said.

Comet Bombardment

Ballentine and colleagues studied krypton and xenon because they're noble gases, so called because they don't mix chemically with most other elements.

As a result, most of Earth's krypton has remained unchanged since its arrival on our planet—allowing scientists to precisely study the conditions of early Earth.

Based on their research, Ballentine and colleagues claim that our atmosphere likely formed when gas and water-rich comets bombarded Earth, shortly after its formation 4.54 billion years ago.