Some of the oldest Earth fossils may just be minerals: Study

Structures previously thought to be fossils, or preserved remains of long dead organisms, may actually be minerals, according to a study that may aid the search for extraterrestrial life during future missions to Mars.

The study, published in the journal Proceedings of the Royal Society B, noted that microscopic tubes and filaments resembling the remains of tiny creatures may have been formed by a process called 'chemical gardening' involving iron-rich minerals.

According to study author Sean McMahon from the University of Edinburgh in the UK, earlier research had suggested such structures to be among the oldest fossils on Earth.

"Such microstructures should therefore not be assumed to represent fossil microbes without independent corroborating evidence," he wrote in the study.

The current study may save future Mars missions valuable time and resources in determining possible signs of life on the Red Planet, McMahon said in a statement.

As part of the research, he created tiny mineral formations in the lab closely mimicking the shape and chemical composition of iron-rich structures commonly found in Mars-like rocks on Earth -- where some examples are thought to be around four billion years old.

McMahon created the structures by mixing iron-rich particles with alkaline liquids containing the chemicals silicate or carbonate.

He said the process -- known as chemical gardening -- occurred naturally where the chemicals abound.

"Chemical reactions like these have been studied for hundreds of years but they had not previously been shown to mimic these tiny iron-rich structures inside rocks. These results call for a re-examination of many ancient real-world examples to see if they are more likely to be fossils or non-biological mineral deposits," said McMahon.

According to the study, these structures can occur in thermal vents on the seabed, and when deep groundwater circulates through pores and fractures in rocks.

The findings suggest that structure alone is not sufficient to confirm whether or not microscopic life-like formations are fossils.

"Here, I show experimentally that abiotic chemical gardening can mimic such purported fossils in both morphology and composition. In particular, chemical gardens meet morphological criteria previously proposed to establish biogenicity, while also producing the precursors to the iron minerals most commonly constitutive of filaments in the rock record," McMahon wrote in the study.

When such formations are found, whether on the Earth or on Mars, McMahon said, more research will be needed to say exactly how they were formed.