Scientists speculate that viruses played a key role in the creation of stromatolites. These are the earliest life forms on Earth.

Life as we know it on Earth might never have arisen if not for viruses. This hypothesis was put forward by scientists studying “living stones” – stromatolites – billions of years old.

In an article published in the journal Trends in Microbiology, a team of scientists from the University of South Wales in Sydney and the United States reviewed the evidence for the oldest life forms in the fossil known as stromatolites. These are layered limestone rocks that are often found in shallow waters around the world. The researchers sought to understand the mechanism that led to the creation of colonies of unicellular organisms (bacterial mats) and, subsequently, stromatolites.

Scientists believe viruses may be the missing piece of the puzzle. Perhaps it was thanks to them that the soft microbial mat was transformed – or lithified – into solid stromatolite elements. They are predominant in places like Shark Bay and Pilbara in Western Australia.

Stromatolites are one of the oldest known microbial ecosystems, dating back about 3.7 billion years. They are widespread in the fossil record and are some of the earliest examples of life on Earth.

Scientists wanted to understand the mechanism of the transformation of microbial mats into stromatolites, not only because very little is known about this process, but also because it can add to scientists’ knowledge about life on Earth and, possibly, on other planets.

The authors postulate that the transition of the bacterial mat from soft cells to stone was enhanced by interaction with viruses. Scientists have suggested that viruses may have a direct or indirect effect on the metabolism of bacteria, which regulates the transition from mat to stone.

In the direct-impact scenario, viruses enter the nucleus of cyanobacteria and affect the host’s metabolism by inserting and removing genes that simultaneously increase the fitness of the virus and the host. This, in turn, increases the survival rate of the microbial mat and selects genes that potentially affect carbonate deposition.

In an indirect scenario, scientists talk about a process known as viral lysis, in which viruses enter living cells and cause their membranes to break down and their contents are released. This actually leads to cell death.