Once life evolved to consume food, instead of harnessing energy from the sun or other chemical sources, picky eaters and gourmands soon followed. Now fossil evidence shows just what was on the menu about 1900 million years ago, and what was the favorite dish.
Like bones with bite marks leftover in a fire, a microfossil assemblage found near Lake Superior in Canada showed that tiny ancient microbes (about 1 micron in size) tended to munch on the larger sheaths (though still really small at 5 microns) of the cyanobacterium-like organism Gunflintia as opposed to the cysts of another bacterium (Huroniospora).
The Gunflintia fossils, found in their namesake Gunflint chert, showed not only perforated sheaths, but also pyritization where iron sulfide (pyrite or â€˜foolâ€™s goldâ€™) replaced the biomaterial of the original sheath â€” a visible marker of a waste product from heterotrophic sulfate-reducing bacteria.
To our modern-day olfactory senses however the ancient Earth would have been a stinky place.
â€œIn fact weâ€™ve all experienced modern bacteria feeding in this way as thatâ€™s where that â€˜rotten eggâ€™ whiff of hydrogen sulfide comes from in a blocked drain. So, rather surprisingly, we can say that life on earth 1,900 million years ago would have smelled a lot like rotten eggs,â€™ said Martin Brasier of Oxford Universityâ€™s Department of Earth Sciences, an author of the study published in this weekâ€™s Proceedings of the National Academy of Sciences (PNAS).