New Theory On How Earth's Atmosphere Became Breathable Proposed By Scientists

Life as we know it requires oxygen. That fact isn't in debate. However, the process behind the increased oxygen levels in the atmosphere of Earth that took place about 2 billion years ago is the subject of debate. A team of scientists has proposed an interesting explanation for the increased oxygen levels in the planet's atmosphere.

Researchers believe that the increasing length of the day resulting from the slowing of Earth's rotation may have allowed microbes to release more oxygen, creating the oxygen-rich atmosphere we have today. Most oxygen on Earth is produced by photosynthesis, which was first seen in organisms known as cyanobacteria when the planet was still uninhabitable.

Cyanobacteria evolved more than 2.4 billion years ago but transforming the planet into the oxygen-rich environment we know today was slow. Researchers don't understand why it took so long and what other factors control the oxygenation of the Earth. Researchers studied mats of cyanobacteria in the Middle Island Sinkhole in Lake Huron in Michigan.

The cyanobacteria live their lives under conditions that resemble the early Earth. In the sinkhole, groundwater seeping out of the lake bottom is very low in oxygen. Life on the bottom of the lake is mainly microbial, and the conditions are an analog for those that prevailed on the planet for billions of years. The microbes are mainly purple oxygen-producing cyanobacteria that compete with white sulfur-oxidizing bacteria.

Researchers say that from dusk until dawn, the sulfur-eating bacteria lie on top of the cyanobacteria blocking access to sunlight. However, when the sun comes out, the sulfur-eaters move downward, and the cyanobacteria rise to the mat's surface. Once the cyanobacteria are at the surface, they're able to photosynthesize and produce oxygen. Researchers found it takes a few hours before they produce oxygen, meaning a long lag in the morning before oxygen production begins. This means the time photosynthesis is limited to only a few hours each day.

This led to researchers hypothesizing the changing length of the day on the ancient Earth could have impacted photosynthesis. Researchers say that days were much shorter when the earth-moon system formed, possibly as short as only six hours.