Layered Lake Reveals Origin of Oxygen in the Atmosphere, Suggests Role of Cyanobacteria in Earth’s Early History

During the early years of the Earth, its atmosphere was very different from what we know today. It lacked the oxygen gas that is essential for the formation of life. Through the study of ancient geological events, experts were able to piece together the story of oxygen buildup in the atmosphere, paving the way for the development of complex life forms.

Unusual Feature of Deming Lake

Deming Lake is considered meromictic, a Greek term that means partially mixing. In most lakes, the water at the top sinks while the water at the bottom rises. This event happens at least once a year because of wind and seasonal changes in temperature that affect the density of water. In Deming Lake, however, the deepest waters never reach the surface, preventing oxygen in its top layer from mixing into its deep layer.

Less than one percent of lakes in the world are meromictic, and most of them have dense, salty bottom waters. Meanwhile, the deep waters of Deming Lake are not very salty but abundant in iron. This makes Deming Lake one of the rarest kinds of meromictic lakes. Its lack of oxygen in its deep layers makes this small body of water similar to early Earth's oceans.

Revelation About Oxygen Buildup

Little Deming Lake may not be famous to visitors in Itasca State Park in Minnesota. However, it has caught the interest of geochemists who are studying the formation of oxygen in the atmosphere 2.4 billion years ago.

A team of researchers led by geochemist Elizabeth D. Swanner conducts several expeditions in Lake Deming every year. In each mission, they row their boats out into the deepest part of the lake, over 60 feet (18 meters).

In one of their expeditions in August, they dropped an anchor and connected their boats in a flotilla as they prepared themselves for the work ahead. A 2-foot-long water pump is lowered while connected to four sensors, which measure the water's temperature, amount of oxygen, pH level, and amount of chlorophyll in every layer they encounter.

Swanner and her colleagues paid special attention to the water layer with high chlorophyll readings. At 20 feet (6 meters) below the surface of Deming Lake, chlorophyll is not found in plants but in cyanobacteria and photosynthetic algae. Despite the abundance of these oxygen-producing organisms, scientists did not detect oxygen at this water level. At this depth, the iron concentrations start to rise to the high levels present at the bottom of the lake.

The scientists conclude that the cyanobacteria that thrive in the chlorophyll- and iron-rich layer of the lake will contain more iron than those that live in the top layer of Deming Lake. If this theory is confirmed, it can help the experts establish that greater success in iron is a motive for staying in the deeper and dimmer layers.

Although the experiments do not explain why it took so long for our planet to build up oxygen, they can still help us understand a piece of it. It provides insight into where oxygen might have been produced, why, and what happened to oxygen in that particular environment.