How did Earth come to have an oxygen atmosphere?

Answer 1

Oxygen was always present in the early atmosphere, but at levels of a few percent only. Measurements have been made in the Banded Iron deposits.

THEN the algae invented photosynthesis and this raised the oxygen level to probably over 20%. This may have been as early as 2.4x109 years ago.

The algae gobbled the CO2 and methane, and eventually all the good greenhouse gases were gone, and Snowball Earth arrived, with temperatures that may have been as low as -50oC at the Equator.

This lasted till the early pre-cambrian, for the volcanoes were still puffing out CO2 etc, and the Earth began to warm again.

Note that photosynthesis is NOT a green process, its essential element is splitting water into H2 and O. The plants/algae can the use the H component to build more complex molecules.

Answer 2

The oxygen in the atmosphere came from photosynthetic organism. Photosynthetic organisms use carbon dioxide, water, and sunlight to produce carbohydrates, which are needed for energy, and oxygen.

Answer 3

Early organisms created oxygen from other gases in the atmosphere.

More specifically, the methane atmosphere on Earth was supplanted by oxygen generated by microorganisms in the oceans. Today, the vast majority of our oxygen comes from the ocean - mainly plants. Earth came to have a oxygen atmostphere because that is the way God invisoned it, so thats how he made it.

Answer 4

Believe it or not, oxygen is a small part of our atmosphere, only about 20%. Most of it is ozone, carbon, nitrogen and other trace gases such as aragon.
Millions of years ago unicellar organisms like archeae and bacteria converted our thick carbon atmosphere into oxygen. This allowed the first plants to grow, ferns and mosses. A few million years after that, the dinosaurs came!

Most of the atmosphere is nitrogen, followed by oxygen, carbon dioxide, carbon monoxide, ozone O3, and traces of other cases like argon, neon, etc. Plants generate the bulk of the oxygen in the air by separating it from carbon dioxide through photosynthesis.

• Nitrogen (N2) 78.084%
• Oxygen (O2) 20.946%
• Argon (Ar) 0.934%
• Carbon dioxide (CO2) 0.0383 %
• Neon (Ne) 0.001818 %
• Helium (He) 0.000524 %
• Methane (CH4) 0.0001745 %
• Krypton (Kr) 0.000114%
• Hydrogen (H2) 0.000055 %
• There is also a varying amount of water vapor, depending on the altitude and conditions where it is measured

Read more:Which_gases_make_up_the_earth's_atmosphere