The largest reservoir of hydrogen on Earth may be hiding in its core

Illustration of Earth's layers showing the molten iron core.

Earth's core contains up to 45 times more hydrogen than the oceans do, making it the largest hydrogen reservoir on the planet, a new study suggests.

Researchers found that this vast amount of hydrogen entered the core during its formation around 4.5 billion years ago, and did not arrive via comets that pummeled Earth once the core was established. The finding could settle the debate about when and how hydrogen was delivered to our planet.