Spot the difference: The left image shows a section from the “Taylor stromatolite,” a fist-sized lump of dried paint that was mistaken for a real stromatolite. Many of its features resemble those found in real stromatolites, shown on the right.

Credit: Nicola McLoughlin et al.

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NEW YORK: Using multi-coloured spray paint, researchers have shown how rock-structures similar to the 'stromatolites' that scientists think are among the earliest fossils on Earth can form in the absence of life.

Stromatolites are chalky mounds built up of layers of microbial secretions and trapped sediments. Fossilised stromatolites discovered in Western Australia have been dated to 3.4 billion years ago, to the so-called Precambrian era.

While some stromatolites contain features which strongly suggest that biology played a major role in their creation, others could conceivably have formed in the absence of life. Distinguishing between biological and "abiotic" stromatolites is an active area of research.

Chance discovery

The new study, detailed in the March issue of the journal Geobiology, is the first to convincingly show in the lab how stromatolite-like structures can form without help from microorganisms.

"Numerical modelling studies have previously shown that laminated stromatolites can be generated by purely abiotic means, but these mathematical studies can be difficult to relate to real world, geological processes," said study team member Nicola McLoughlin, a geologist at the University of Bergen in Norway.

McLoughlin and her colleagues used enamel spray paint to create layers resembling those seen in stromatolites. They got the idea for their study after discovering that a piece of "rock" in a fossil collection, which was thought to be a stromatolite, was actually a chunk of dried, multi-layered paint.

To recreate this effect in the lab, the team sprayed a coat of paint onto a horizontal surface, let it dry, and applied another coat. They alternated between red, white, and black paint so that the layers could be easily traced. Doing this for six weeks resulted in creating a hard structure made of dried paint that was several centimetres thick.

The team's "paint stromatolite" contained laminated features similar to those found in naturally occurring stromatolites, such as wrinkles, whirls and wave patterns. "In the rock record, these things may take hundreds to thousands of years to form, but we can use different coloured spray paint layers in the lab to try and understand some of the physics of the fluid flow and processes that are shaping these stromatolites in real time," McLoughlin said.

Problems of interpretation

Nora Noffke, a geobiologist at Old Dominion University in Virginia, U.S., said the new findings are a "call to caution" for scientists. The study "documents how severe the problem of interpretation of the spotty geological record of the [early Precambrian] is," said Noffke, who was not involved in the study.

McLoughlin likened stromatolites to the Rosetta stone that allowed Egyptologists to decipher hieroglyphics. She said that an improved understanding of how different stromatolite shapes formed could help scientists understand how life evolved through the eons.

"If we could better understand [that]… we could then begin to understand how for example, climate change and microbial evolution is recorded in the changes in abundance and morphology of stromatolites through time," she said.