Ancient Fossils Provide Clues as to What Early Earth Smelled Like: Eggs, Not Roses

About 1,900 million years ago, our ancient Earth was a different place. Tiny organisms feasted on each other, swarming through the primordial soup of our ancient seas. Now, researchers have direct evidence of these prehistoric interactions. They've discovered fossils in rocks around Lake Superior that give them a glimpse into Earth's past.

The fossils themselves actually capture ancient microbes in the act of feasting on a cyanobacteria-like fossil called Gunflintia. More specifically, the researchers found the perforated sheathes of Gunflintia being discarded as the leftovers of the meal. In many places, the tiny fossils had been partially or entirely replaced with iron sulfide, also known as fool's good, which is a waste product of heterotrphic sulfate-reducing bacteria that is also a highly visible marker. In fact, the fossils actually demonstrate a type of feeding called "heterotrophy."

"What we call 'heterotrophy' is the same thing we do after dinner as the bacteria in our gut break down organic matter," said Martin Brasier of Oxford University's Department of Earth Sciences in a news release. "Whilst there is chemical evidence suggesting that this mode of feeding dates back 3,500 million years, in this study for the first time we identify how it was happening and 'who was eating who.'"

The same type of feeding can be seen in modern bacteria, which is where that "rotten egg" smell from a blocked drain comes from. The fact that this type of feeding is seen today actually suggests that during the early stages of our planet, things smelled pretty badly.

"Recent geochemical analyses have shown that sulfur-based activities of bacteria can likely be traced back to 3,500 million years or so," said lead researcher David Wacey in a news release. "Whilst the Gunflint (Gunflintia) fossils are only about half as old, they confirm that such bacteria were indeed flourishing by 1,900 million years ago, and that they were also highly particular about what they chose to eat."

The findings have given researchers a new glimpse at our early Earth, and could provide further clues as to how ancient organisms evolved and thrived during that time.

The findings are published in the journal Proceedings of the National Academy of Sciences.