Which of the following caused the addition of free oxygen to earth’s early atmosphere?

a. volcanic eruptions
b. photosynthesis by cyanobacteria
c. photosynthesis by land plants
d. meteorite impacts

The correct answer is option B.photosynthesis by cyanobacteria.

Explanation:

Oxygen is something vital for life on our planet.

In the beginning our planet did not have an atmosphere in which we could breathe, but it was full of poisonous gases. What produced oxygen on Earth were primitive algae through the process of photosynthesis.

While there is no precision when life on Earth was created, it is believed that primitive organisms such as algae and bacteria were the first to inhabit our planet, and that they lived in the ocean.

Thanks to the process of photosynthesis, plants transform sunlight, water and carbon dioxide into oxygen that is released into the atmosphere. These primitive algae known as cyanobacteria, it is likely that they could not generate the process of photosynthesis but a very similar process called chemosynthesis, allowing them to bring oxygen to Earth.

Here the plants use a chemical energy instead of the energy coming from the sun and can generate food. With organisms such as bacteria generating their own food through chemical energy, algae and other bacteria had the chance to create photosynthesis. This process happened 2,500 and 2,300 million years ago, where the oxygen in the atmosphere began to change in a way very similar to what it is today. This was what we call the great oxygenation event.