Lifeforms

Dear Kristina,
The oldest known lifeform on earth (as far I know) is recorded in Western Australia and South Africa.
The dating is 3500 to 3000 Ma (millions of years) what is called te Early Archean. There about some fossilized filaments (like small pieces of wire)and "uncommon microfossils" in rocks.
Also there were some micro organisme who builded large mats in small layers. We find these mats fossilized and called them "stromatolites".

You must remember that we only find lifeforms which are fossilized, probably there where lifeforms who did n't fossilized (because there body did not contain chemicals who could be fossilized).So we do not know anything about them.

- In short
In the Early Archean (3500 -300 Ma) there was life present. Microbial (micro bacterial & one cellular) ecosystems were driven by autotrophy (that means the could feed themselves by using for instance the sulfur or other minerals of the rocks they were growing on)
(there was probably some oxigen in the air rougly 1-2% of present-day levels)
Most likely there were present photoautotrophic (they needed light)and oxygenic (they needed oxigen) cyanobacteria (blue colored bacteria). And mayby there were already some forms who could "eat" those bacteria by means of phagocystosis. (This bacteria surrounded with it's body an other bacteria and begins to dissolve it)

I hope that you can use this answer!

This early Archean ecosystems, are very interesting but very difficult to understand.

With regards

Dr. H.B. Eland