Question

What is the lithosphere's temperature?

Answer 1

Geothermal gradient ( rate of change of temperature) varies from surface to the center. Average for lithosphere: Surface temperature 15 deg C at the top and about 1300 deg C at the bottom.

Explanation:

The thickness of lithosphere under sea is nearly 200 Km and this is nearly double of the layer under land. The increase-rate might be slower, under the sea.