An international team utilized advanced X-ray technology to detect and map arsenic within 2.1-billion-year-old fossils discovered in the Francevillian Basin in Gabon.According to the researchers, the arsenic found in these fossils was not due to later contamination but rather a biological response to environmental stress.

Distinct patterns observed in the arsenic preservation process within the fossils, when compared to structures left by non-living minerals, provide further evidence that these fossils were once complex living organisms with advanced cells. The study, published in Nature Communications, offers new insights into how early life confronted environmental challenges and underscores the crucial role of adaptation in the evolution of life.

“The ability to cope with arsenic was not something eukaryotes developed randomly,” said dr Ernest Chi Fru, a co-author of the paper and Reader at Cardiff University’s School of Earth and Environmental Sciences. “It coincided with a period of significant environmental change, when oxygen levels in the Earth’s atmosphere first rose. This increase in oxygen also led to a rise in arsenate, a particularly toxic form of arsenic which competes with phosphate, a vital nutrient for all life, making Earth’s oceans a dangerous place.”

The research builds upon the team’s prior work on the 2.1-billion-year-old Francevillian biota, which they believe emerged after a local underwater volcanic event caused a sudden surge of nutrients into a small, enclosed sea. This nutrient boost aided the local thriving of these early life forms,according to the team,which was led by Université de Poitiers and Cardiff University.

Dr. Chi Fru added, “We looked at the evolution of arsenic in the Francevillian basin’s seawater before and after the fossils. It was actually quite low in arsenic concentration at the time when these primitive eukaryotes evolved, leading us to think they should have lived there quite happily.”

“However, the surprisingly high levels of arsenic stored in their bodies, revealed in our analysis, suggest that they were extremely sensitive to even low levels of arsenic in seawater.”

The organisms eventually became extinct when volcanic activity recurred in the area, and oxygen levels in the seawater decreased, according to the team. Their disappearance suggests that the ability of complex life to protect itself from toxic substances like arsenic, by safely storing it inside cells, may have evolved more than once in Earth’s history.

“All living things have ways to protect themselves from arsenic, which is toxic to life,” Dr Chi Fru said. “In the ocean, tiny plankton near the surface – the same ones that make about half the oxygen in the air we breathe – are always working to get rid of arsenic from their bodies. They can’t avoid it because arsenic is naturally in the water, and their cells can’t easily tell the difference between arsenate and phosphate, a nutrient they actually need. this was true even in ancient times, just like it is today.”

“We know these ancient organisms went extinct,so the way modern life handles arsenic didn’t come directly from them.”

Implications for Understanding Early Life

This discovery provides critical insights into the strategies early life forms employed to survive in a challenging environment.The ability to detoxify arsenic may have been a key factor in the evolution and diversification of early life on Earth.

So,it was really vital for organisms such as eukaryotes to have strategies to cope with this most toxic of elements,once known in Europe as ‘inheritance powder’ because of its deadly use in poisonings.

The Role of Arsenic in Early Earth

Arsenic, while toxic, has played a significant role in the geochemical processes of early Earth. Understanding how early life forms interacted with arsenic can shed light on the conditions that allowed life to emerge and evolve.