Meredith Fore writes:

Putting together the history of life on Earth has a major stumbling block: Prior to about 540 million years ago, most life was squishy and microbial, which meant it rarely fossilized. This major blind spot makes it difficult for researchers to study ancient life at a key point in Earth’s evolutionary history, and even more difficult to potentially find evidence of ancient microbial life on Mars. But a recent study of kaolinite, an aluminum-rich clay, gives researchers some major hints about where to start looking.

In 1859, Charles Darwin was at a loss. Plenty of fossils of multi-celled and large animals had been found, but there seemed to be no fossils of those animals’ more basic evolutionary ancestors. His theory of evolution, however, contended that life must have existed for eons before then. “To the question why we do not find records of these vast primordial periods, I can give no satisfactory answer,” he wrote in “On the Origin of Species.”

We now know the answer to his question: Fossilization of an organism with no shell or skeleton is incredibly rare. Before about 540 million years ago, when the age known as the Cambrian began and multicellular life rapidly diversified, the only living things on Earth were small — microbes, bacteria and algae. They lacked the hard components that would have allowed their bodies to be more easily fossilized.

“When we try to reconstruct the study of life billions of years ago, we find only pieces of the puzzle,” said Emmanuelle Javaux, a geobiologist at the University of Liege in Belgium. “It’s important to understand what they really represent.”

A new study by researchers at Yale University in New Haven, Connecticut and the University of Oxford in the U.K. analyzed pre-Cambrian fossils to understand how they were created. The analysis showed “halos” of a specific type of clay, kaolinite, around microbial fossils, suggesting that kaolinite is particularly good at preserving these traces of life. [Continue reading…]