The origins of water on Earth have been debated by scientists for hundreds of years. Some believe that water was delivered by comets, but recently, there has been mounting evidence for a different explanation.
To explore this theory, we have to wind the geologic clock back 4 billion years to a time when the Earth was hot and still forming. The idea is that water has always been on Earth. Trapped beneath the crust, it's locked in liquid magma.
But as the Earth's surface began to cool and harden, volcanoes acted like a tear in the fabric of our planet, allowing the water to slowly escape.
This water vapor then condensed in our atmosphere and fell as rain. It rained for so long that eventually, our dry, barren Earth turned into a Blue Planet.
Water that we see on Earth mostly comes from volcanoes. Without volcanoes, there wouldn't be life on Earth, literally.
