# How deep must Earth's ocean be to form Ice VII on bottom?

Is there way to tell how deep must Earth's ocean be to form Ice VII on bottom? Or is it impossible because of our planet is too small?

As I know, in 11.5km Mariana Trench there is 108 MPa and to form Ice VII u need 3GPa. But 11.5km is nothing compared to size of Earth right?

• can we extend this question to include ice VI? – Paul Young Oct 5 at 18:36
• oh, and Ice III and V as well ... it is cold at the bottom on the ocean – Paul Young Oct 5 at 18:47

Ice VII occurs above 3 GPa. Pressure at depth $$z$$ is $$p =\rho g z$$, so the critical depth for $$\rho=1050$$ kg/m$$^3$$ is $$z=290,951.4$$ m. So we need a 291 km deep ocean to get high pressure ice. Not very likely on Earth.