Antarctica’s Time Capsule that Contains the Secret of Photosynthesis

There are probably not a few people who go on a so-called LAN trip during the summer vacation season, when the hot weather continues. Among them, looking at the coldest places on earth may help to cool off.

A freshwater lake located under the ice of Antarctica is not only a very important place in Antarctica, but also a lake of very special significance worldwide. This is because, like a time capsule, it retains the appearance of the ancient Earth, and holds clues to explain the birth and evolution of life and, in particular, the origin of photosynthesis.

Oxygen currently makes up about 21% of Earth’s atmosphere, but other planets such as Venus and Mars have little oxygen in their atmospheres. Of course, the Earth also had little oxygen when it was first born, but it has been transformed into a planet rich in oxygen by photosynthetic cyanobacteria and plants. In particular, about 2 billion years ago, there was a great oxidation event in which the concentration of oxygen in the earth’s atmosphere suddenly increased by more than 10,000 times. reach

Lake Untersee in Antarctica is considered as the place where clues to the origin of oxygen, the first photosynthesis, can be found in Earth’s history. The lake is located on the northern edge of Antarctica’s so-called Queen Maud Land, and is surrounded by rugged mountains and glaciers. The length of the lake is about 6.5 km and the width is 2.5 km, making it a very large freshwater lake in Antarctica. It was discovered by German Antarctic expeditions around 1938, and was named Lake Untersee, which means undersea or underwater in German.

Because this lake has been isolated for a long time, it not only provides invaluable data for studying the history of the earth, but also has special significance in terms of astrobiology. In other words, in addition to Mars, Jupiter’s moon Titan and Saturn’s moon Enceladus are considered as places where life is likely to exist in the solar system. However, it is because Titan and Enceladus have a liquid sea covered with ice, and the environment is supposed to be quite similar to Lake Unterje. In addition, the fact that Lake Unterje has a higher methane content than other lakes on Earth can also be a good reference for the study of extraterrestrial primitive life.

Since 2008, an international expedition led by astrobiologists belonging to the National Aeronautics and Space Administration (NASA) has started exploring Lake Unterje in earnest. After making a hole in the ice on the surface of the lake, they put on their diving equipment and dived into the water to look, and they witnessed a beautiful and mysterious sight beneath the lake. In other words, it is because a lot of topography that looks like a cone protruding from the bottom of the lake covered in light blue was found. The largest of the cone-shaped topography was about 50 cm high, and its identity was none other than a microbial mat, that is, stromatolites.

The bottom of Lake Unterje, a unique cone-shaped topography ⓒ Dale Andersen

Stromatolite is a layered sedimentary structure of cyanobacteria, or cyanobacteria, as they grow. Cyanobacteria are the first photosynthetic single-celled organisms in the history of the Earth. However, since cyanobacteria usually form layers on a flat surface, cone-shaped stromatolites are very difficult to find elsewhere. A similar cone-shaped microbial mat fossil has been found in Western Australia.

It was at the bottom of the sea 3.4 billion years ago, and the unique cone shape of the two stromatolites proves once again that Lake Untersee was the same environment as the ancient Earth. It is explained that the cyanobacteria that live at the bottom of the dark lake may have grown upwards to absorb light as efficiently as possible.

In addition, as a result of collecting and analyzing cones from Unterje Lake, it was found that the surface was covered with a structure such as fine threads or nets. Biologists speculate that such a structure may have been made to increase the surface area to increase the contact area with water, which provides nutrients, or to better receive the light needed for photosynthesis in low light.

Cyanobacteria on the microbial mat ⓒ Wikimedia

It is believed that primitive life forms that were first born on Earth may have made organic matter necessary for survival by using sulfur compounds spewing out from hot places. Cyanobacteria, on the other hand, have created a revolutionary way of using solar energy to generate organic matter from carbon dioxide and water, which means that oxygen is the first on Earth. A more in-depth study of the environment of Lake Unterje and its cyanobacteria will help us to not only unravel the secrets of photosynthesis and oxygenation, but also to reveal the existence of extraterrestrial life.