How did earths atmosphere get its free oxygen?

Answer 1

Releasing oxygen into the atmosphereA number of billions of years ago there was no oxygen in the atmosphere. In fact oxygen was a poison to everything that lived. At some point in this distant past, a bacteria managed to absorb a smaller cell that used chlorophyll to photosynthesise. This became a symbiosis relationship where the bacteria protected the little cell, while the little cell fed the bacteria.

This successful harmony resulted in a large number of photosynthesising cells that take water (H2O - dihydrogen oxide) and used sunlight as the power source to extract the hydrogen for food and release the oxygen. The released oxygen found it's way into the atmosphere. This is the exact chemical reaction that continues today in all plants and algae.

Ok, for those on Study Island the answer is the free oxygen bubbled up from the oceans.

Answer 2

A number of billions of years ago there was no oxygen in the atmosphere. In fact oxygen was a poison to everything that lived. At some point in this distant past, a bacteria managed to absorb a smaller cell that used chlorophyll to photosynthesise. This became a symbiosis relationship where the bacteria protected the little cell, while the little cell fed the bacteria.

This successful harmony resulted in a large number of photosynthesising cells that take water (H2O - dihydrogen oxide) and used sunlight as the power source to extract the hydrogen for food and release the oxygen. The released oxygen found it's way into the atmosphere. This is the exact chemical reaction that continues today in all plants and algae.

Answer 3

• when photosynthetic bacteria first evolved.