On: Earth may have been a 'water world' 3B years ago, scientists find

[samatman]

A note to anyone who wants to follow up on this lead: these are called stromatolites.

[andrewflnr → samatman]

Stromatolites are specifically fossilized bacterial colonies. Nothing GP said was about stromatolites, just "rocks".

People should definitely go look up stromatolites, though. They're cool.

[amelius → samatman]

So, were they completely immersed in water?

[samatman → amelius]

They formed in shallow water, so to begin with, yes.

[Tagbert → amelius]

Tidal pools