Ancient South Africa Rocks Reveal Life on Land May Have Started 300 Million Years Earlier

A new study of the ancient rock formations in South Africa revealed that life on land may have begun some 300 million years earlier than previously thought.

The study, published in the journal Geology, showed evidence of microbial activity occurring on land at least as early as 3.2 billion years ago. Their discovery was based on the presence of tiny grains of iron sulfide mineral pyrite on the 3.22 billion-year old layer of South Africa's Barberton greenstone belt.

According to a press release, the ancient rock formation in Barberton greenstone belt is considered to be one of the oldest rocks on Earth, with their formation dating back 3.5 billion years ago. The telltale signs of microbial activity in the tiny grains of the iron sulfide mineral pyrite were recorded both in trace element distributions as well as in the ratio between the sulfur isotopes 34S and 32S in the pyrite.

Using sample masses less than one billionth of a gram, the researchers were able to determine the 34S/32S ratio. Furthermore, the composition of the rock, the shape of the crystals and visible layer in the field indicate that the sample rock indeed came from an ancient soil profile.

The researchers found that the fraction of 34S in the core of some crystals have different characteristics compared to its rim. This suggests that the rim of the crystal was involved in a microbial processing of sulfur, called biogenic fractionation. Furthermore, field data collected by the researchers showed that a braided river system must have transported the sediment containing the iron sulfide crystals.

Noting the continual shift between wet and dry conditions, the researchers suggest that microbes living in the soil were responsible for the rim overgrowths on the pyrite crystals. With these findings, the researchers conclude that microbial life on land may have started 300 million years earlier than previously documented.