The oldest lake on Earth

The world's oldest lake is not only a precious natural heritage but also contains important scientific information about the history of the Earth. One of the oldest lakes is Lake Baikal in Russia, which has existed for about 25 million years.

Lake Baikal is a giant freshwater lake in southeastern Siberia, according to Ted Ozersky , an associate professor of lakes and other inland waters at the University of Minnesota. The second-oldest lake on the planet is Issyk-Kul in Kyrgyzstan, which formed about 20 million years ago.

Baikal is the oldest and deepest lake in the world.

Lake Baikal covers an area of ​​31,700 square kilometers, making it the seventh largest lake in the world. Not only is it the oldest, it is also the deepest, at about 1.6 kilometers deep. But that's just the depth of the water. The actual basin is much deeper, with 5 to 7 kilometers of sediment at the bottom, according to Ozersky. In the case of Lake Baikal, researchers used seismic surveys to estimate the average sediment formation rate.

This sediment is key to determining the age of the lake. Researchers do this using radiometric dating, which measures the ratio of radioactive isotopes. In this case, they analyze lake sediment for radioactive versions of cesium, lead, and carbon. The analysis reveals the ages of the different sediment layers and the rate at which they were deposited.

Understanding how lakes form can help researchers better understand how they persist over millions of years. Many lakes are formed by glaciers, says Mark Edlund, senior scientist and director of aquatic collections at the Science Museum of Minnesota. Glaciers carve holes in the landscape and leave behind chunks of ice. That ice then melts, filling the holes. ' In the grand scheme of things, they're short-lived systems ,' Edlund says.

Baikal is a rift lake, which forms when two continental plates begin to move apart, creating a deep rift. As the plates continue to separate, the rift continues to deepen. ' As a result, that area never fills ,' says Edlund. That's why rift lakes can last so long.

Lake Baikal is expanding by 2.5 centimeters per year, Ozersky said. Several other ancient lakes around the world, such as Lake Malawi (5 million years old) and Lake Tanganyika (12 million years old) - both in Southeast Africa - also formed from rifts.

Baikal is considered the most biodiverse lake on the planet. " Evolution has had a lot of time to take place in the lake ecosystem without interruption ," Ozersky explains.

The lake also has the highest proportion of endemic plants and animals—species found nowhere else on Earth. Perhaps the most notable of these is the Baikal seal ( Pusa sibirica ), the only freshwater seal species. Several other seal species can live in the lakes, but they 'invaded' the lake from rivers and streams, Ozersky notes. Lake Baikal is also home to hundreds of species of freshwater shrimp, giving scientists the opportunity to study speciation and diversification.

Edlund studies diatoms, a type of single-celled algae. These organisms take dissolved silica from the water and turn it into bioglass, which they coat themselves with. Diatoms are typically 10 to 50 micrometers in diameter (about half the width of a human hair), but the diatoms in Baikal are unusually large, measuring 50 to 150 micrometers. ' When you look at the diatoms in Lake Baikal, they really blow your mind, ' Edlund says.

The average surface temperature of Lake Baikal is just 4 degrees Celsius. " It's a cold lake. If you want to swim in it, you have to be mentally prepared ," says Edlund.