[blakestyger]

I know the usual basic stuff but where I'm stuck is how they don't appear to have changed significantly since they appeared in the fossil record ca. 2.5 bnya.

If the cyanobacteria are more or less the same as now what does it say about them if they can remain unchanged during all the envirinmental changes since then? Is it true to say that they have not evolved?

Any insights would be welcome, thanks.

[LeeE]

Interesting question; yes, you'd expect them to have changed more than they appear to have done.  Dunno.

[Mazurka]

Strictly speaking stromatolites are strucutres formed by colonies of different microbes and close study shows significant changes. Not all stromatolites are conclusively biological in origin, but the oldest biological stromatolites are bacteria whilst younger tend to be algae.

The descendants of others evolved into other living things not recognisable as bacteria...

Cyanobacteria "work" - they can produce energy and reproduce - they fit a particular (large and varied) ecological niche - from deserts to oceans via hypersaline lakes where modern stromatolite structures are found.