And the speed at which it happens:

> a cold, round anomaly about 200 km below the surface.

> By estimating how far the drip had fallen and calculating the speed of its descent, the researchers estimate that the drip broke off between 2 and 5 million years ago.

A few megayears later, the bit that broke off is still falling.

200km in 2m years, I make that in the ballpark of 0.1m per year - a bit less if it's > 2m years, and started below the surface.