When Did Atolls Form?

The atolls we see today started forming around 400,000 years ago, the authors argue, in the middle of an exceptionally warm period when sea levels were about 20 meters higher than they are today.

What is the origin of atolls?

This circular type of coral reef, called an atoll, is created as a ring of coral surrounds an undersea volcano that has risen above the water's surface. Long after the volcano has receded into the ocean, the atoll remains.

How old is the atoll?

Atolls form as oceanic volcanoes erupt and grow above the water line, then erode to sea level. In the case of Midway, that process began 28 million years ago, making it the second oldest of the Hawaiian chain. Underwater coral reefs ring the eroding mountain, which can leave a few islands behind as high ground.