From New Scientist:
3 billion-year-old fossils show early microbes lived in cavities
They looked much like bacteria today, and the cavities protected them.
The find creates hope for life on Mars. 
“The record of Archaean microfossils is sparse and controversial,” says Birger Rasmussen at Curtin University, Australia, who previously reported the discovery of cavity-dwelling microbes in 2.7 billion-year-old sediments in Australia. “This is an exciting find as it extends the record of possible life in this habitat a further 500 million years.” More.
Hmmm. More time for life, less for Darwin.
See also: Ocean toxicity slowed rapid evolution of complex life?
and What we know and don’t know about the origin of life
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