[sgt101]

My thoughts:

Civilisation implies large scale agriculture.

Large scale agriculture implies specific pollen signatures.

We don't see any of these signatures in the pollen records dredged up from lakes and seas.

There was no previous civilisation in the last 1.4m years (this is the depth of the pollen records we have I think).

[saidnooneever]

it could essentially be much longer ago, but you are right and imho this is strongest evidence. civilizations dont need to evolve to high technology to be a relatively advanced civilization and say, build pyramids. but they do need plenty of food structurally available in any larger numbers than 'big tribe'

[gregdaniels421]

The proper Silurian period had no pollen, so that wouldn't make any sense.