Fossil evolution study sheds new light on life's transition from water to land

Fossil evolution study evidence suggests that organisms may have populated land much earlier than we thought.

When did living organisms first leave the water for land? Just 20 years ago, scientists believed microscopic life first emerged onto land 1.2 billion years ago. However, fossil evidence has been steadily pushing that estimate earlier over the past two decades, with a recent theory showing the earliest evidence of life on land 2.9 billion years ago.

Now, it’s taking another leap backwards.

A team of scientists led by Sami Nabhan of the Freie Universität Berlin has discovered signs that microbes lived on land as early as 3.2 billion years ago. The team has been studying ancient rock formations in the Barberton greenstone belt of South Africa.

Though the formations they were studying range to 3.5 billion years old, the layer that showed signs of microbial life was dated to 3.22 billion years ago.

Elements in the layer, including grains of iron pyrite, showed evidence of microbe activity. Instrumentation showed that a number of crystals had signs of “biogenic fractionation” – when microbes process sulfur from the exterior of the grains.

The fossil evolution study was conducted by Michael Wiedenbeck at the GFZ German Research Centre for Geosciences’ secondary ion mass spectrometry lab.

The rock formations where the fossil evidence was found appear once to have been the floodplain of an ancient river. Scientists believe the microbes may have been carried onto land in sediment carried by the river, then adapted to living out of water due to the cycling between flooding and dry conditions.

In 1999, NASA scientist Dr. Hiroshi Ohmoto discovered evidence of rock formations – “laterites” that indicate microbe activity – dated to 2.3 billion years old. In 2002, an international team of scientists discovered fossilized microbial mats that were approximately 2.6 billion years old. A 2013 paper by Hugo Beraldi-Campesi pointed to the abundance of microbial life in water 3.5 billion years ago and suggested that the microbes could have adapted to terrestrial life in coastal areas between 3.4 and 3.5 billion years ago.

Determining when and why microbes first adapted to dryland conditions may help scientists better understand why species evolve and adapt to previously hostile conditions, as well as the impact these adaptations have on other species and environments.