How did earth come to have an oxygen atmosphere?

The answer is tiny organisms known as cyanobacteria, or blue-green algae. These microbes conduct photosynthesis: using sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen. "What it looks like is that oxygen was first produced somewhere around 2.7 billion to 2.8 billon years ago. read more

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. read more

The early oxygen from cyanobacteria may have been destroyed by a preponderance of methane. The two gases react with each other to produce carbon dioxide and water. "Oxygen can't accumulate in a methane-rich environment," Papineau says. read more

Yet no one has come up with a rock-solid test to determine the precise oxygen content of the atmosphere at any given time from the geologic record. But one thing is clear—the origins of oxygen in Earth's atmosphere derive from one thing: life. read more