Lake Baikal is 25 million years old, making it the oldest lake on the planet. (Photo courtesy of Tatyana Andreeva via Shutterstock)
Like mountains, lakes on Earth can be very old, or more than 1 million years old. There are only 20 ancient lakes in the world, but which one is the oldest?
There’s a clear winner when it comes to the oldest lake on Earth: Lake Baikal, located in southeastern Siberia. Research suggests that this vast body of freshwater is 25 million years old, according to Ted Ozersky, an associate professor of biological limnology at the University of Minnesota. Meanwhile, the Great Lakes formed less than 20,000 years ago. The second-oldest lake is Issyk-Kul in Kyrgyzstan, which formed about 20 million years ago.
Lake Baikal covers 12,239 square miles (31,700 square kilometers), making it the seventh-largest lake in the world. Not only is it the oldest lake on the planet, it’s also the deepest, reaching about 1 mile (1.6 kilometers) deep. That’s just the depth of the water, though. “The actual depth of the body of water is well over a mile,” Ozersky told Live Science, adding that 3.1 to 4.3 miles (5 to 7 kilometers) of that is sediment on the bottom. In the case of Baikal, where there are miles of sediment, scientists use seismic studies to determine the average rate of sediment accumulation, Ozersky added.
This sediment plays an important role in determining the age of the lake. Scientists use isotopic dating to measure the age of the lake. This method involves analyzing the ratios of radioactive isotopes. In this case, limnologists examine the lake sediments for radioactive forms of cesium, lead, and carbon. This analysis provides information about the age of the different layers of sediment and how quickly they accumulated, Ozersky explained.
By studying how lakes — and Lake Baikal in particular — form, researchers can better understand how it has survived for millions of years. Many lakes are formed by glacial activity, Mark Edlund, a senior scientist and director of aquatic research and collections at the Science Museum of Minnesota, told Live Science. Glaciers carve depressions in the landscape and leave behind chunks of ice that melt over time and fill the holes. “But these are generally very short-lived systems,” Edlund added.
In contrast, Lake Baikal is a rift lake. Rift lakes form when two continental plates begin to move away from each other, creating a crack. This crack is called a graben. As the plates move further apart, the graben continues to deepen. “That’s why this area never fills up,” Edlund explained, which is what allows rift lakes to last so long.
In fact, Lake Baikal is expanding by an inch (2.5 centimeters) every year, Ozersky says. Some of the world's other oldest lakes, such as Lake Malawi (up to 5 million years old) and Lake Tanganyika (up to 12 million years old), were also formed by faults.
Ozersky also points out that Lake Baikal can lay claim to the title of the most biologically diverse lake on the planet.
Sourse: www.livescience.com
