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

Question

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?

oh, and Ice III and V as well ... it is cold at the bottom on the ocean — Paul Young, Oct 05 '19 at 18:47

score 0 · Accepted Answer · edited Oct 05 '19 at 18:31

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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.

edited Oct 05 '19 at 18:31

Thomas Fritsch

39,317

answered Oct 05 '19 at 18:13

Anders Sandberg

32,067

On this image is rough representation of this 290,9km deep sea: https://imgur.com/a/SopRncv . I think its 100% possible :D :D :D Thanks for answer. – Baterka Oct 05 '19 at 19:40
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@Baterka - I would like to draw your attention to the maximum height of mountains when you consider the maximum depth of a trench in the earth filled with water ... the density of water is only about 1/3 that of granite – Paul Young Oct 05 '19 at 21:04

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

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