Whether you’re on a boat or in a bathtub, a leak isn’t good. But our world could be facing a leak much bigger than a dripping faucet or oil spill. The core of the Earth is leaking, and if that wasn’t bad enough, scientists don’t know why.

What is the Earth’s core, and how can we tell that it’s leaking?

The Earth’s interior is divided up into layers: the crust, the mantle, the outer core, and the inner core. For the most part, these layers are independent and easy to identify because of their different ingredients and behaviors; for example, the innermost part of the Earth’s core is solid while the outer core is liquid. The outer core is made of incredibly hot liquid (about as hot as the surface of the sun), and it moves and churns around the solid inner core. However, even though these layers are usually separate, scientists have found evidence that materials from the core are moving through the mantle and up to the crust, the outer edge of the planet that we all call home.

Scientists have predicted that the layers of the Earth exchange materials all the time, but since the layers of the Earth are so hot and so deep, scientists can’t just dig a big hole and take samples of different layers to compare and contrast. The deepest hole humans have ever dug, the Kola Superdeep Borehole in Russia, is almost 7.6 miles deep; the core doesn’t start until nearly 1,800 miles down. In order to discover whether or not the core was actually leaking material into the upper layers of the planet, scientists had to get creative.

Instead of digging to the center of the Earth, scientists instead picked up some old rocks on the crust itself. By tracking the amount of tungsten in rocks on the Earth’s surface, scientists around the world have identified an amount of tungsten consistent with the leaking-core theory. This suggests that perhaps the layers of the Earth frequently exchange materials; one strong theory is that oxygen-rich materials move down through the Earth from the crust, prompting tungsten-rich materials to rise up in an unusual inner-Earth trade deal. But additional research shows that this hasn’t always been the case.

How long has the Earth’s core been leaking?

When scientists began studying the tungsten content of rocks to determine whether or not elemental materials from the core were leaking up onto the surface of the Earth, they discovered something even more interesting than a high tungsten content. Some of the oldest rocks tested had drastically different tungsten contents than the newer rocks did. Rocks that were between 4.3 billion years old and 2.7 billion years old didn’t show any evidence of core-based tungsten. When they tested rocks younger than 2.5 billion years old, however, the tungsten content and type changed drastically: the rocks contained high levels of tungsten from the core. Why? No one really knows. Theories and experiments are underway, but right now, there isn’t a clear reason for the Earth’s sudden transfer of materials.

What does the leak mean for the planet?

Even though the Earth’s core has been leaking for billions of years, that doesn’t mean it’s normal or healthy. In fact, substantial leaking could cause our planet to change dramatically and drastically. The Earth’s core doesn’t just provide a nice resting place for the mantle and the crust, it gives the planet a protective magnetic field that keeps radiation and solar particles from intruding. If the core leaks too much, the planet could be at risk of losing its protection and even its habitability.