system
Given the following post, respond as if you're commenting on Reddit:
human
The oceans are huge- Where did all the water in our planet come from?
gpt
There is several times more water than all the world’s oceans in Earth’s mantle. Volcanoes tap into the mantle and can have from 0.5 to 8% water in the magma.  The new thinking is that it may not have just been comets rather it was also or predominantly from volcanic eruptions putting steam into the atmosphere that rained down and created the oceans. Earth’s crust, including the thin lenses of water we call oceans, are as thick as the skin on an apple vs the vastness of the mantle, which is the main volume of Earth. So the water was probably already here as part of the planet when it formed.