Deep down beneath our feet, the Earth makes a tiny, quiet thump every 26 seconds, kind of like a slow heartbeat. This small shaking is too faint for us to feel, but scientists have used special tools called seismometers to notice it across different parts of the world. They call this a “microseism”—a tiny Earth shake. No one really knows why it happens, but it keeps going, steady and unchanging. Some ideas are that big ocean waves might cause it, like tapping on a table.

Others think there might be volcanoes nearby that cause the tremors. But even after many years of studying it, scientists still don’t know for sure why it happens. In 2005, some scientists at the University of Colorado found the same quiet thumping again. They traced it back to a place near West Africa called the Gulf of Guinea. They wondered what could be making Earth shake like that. A long time ago, in the 1960s, a scientist named Jack Oliver first saw this strange heartbeat. He thought it came from the ocean near the middle of the Atlantic.

It even got a little stronger during good weather seasons. But back then, they didn’t have all the fancy tools we have now, so his idea was just a guess. What’s interesting is that every 26 seconds, Earth seems to be ticking like a giant clock. We don’t know what makes it do that, and it’s a mystery hiding under the ocean and rocks. And the strangest part? It hasn’t stopped yet.