New research published in Science Advances describes complex structures in rocks from Quebec, Canada, estimated to be between 3.75 and 4.28 billion years old and of possible organic origin.
The structures found in Canada are more than 200 to 700 million years older than the previous oldest fossils of microbes found in Australia. They formed just 100 to 300 million years after the conditions on Earth became favorable for life.
The researchers discovered the structures in iron- and silica-rich sediments deposited near hydrothermal vents on a former seafloor. As the ocean closed, the oceanic crust was lifted up, merging with the continental core of what is now the Canadian Shield and becoming part of the Nuvvuagittuq Supracrustal Belt.
While some of the structures could conceivably have been created through chance chemical reactions, their overall complexity suggests that they most likely are biological in origin, as no structure created via chemistry alone has been found like it.
The most complex microfossil consists of a stem with parallel branches on one side that is nearly a centimeter long. Others resemble distorted spheres, tubes, and filaments. These new findings suggest that a variety of microbial life may have existed on primordial Earth.
The explanation of the structures as remains of former life-forms is not new, but the study provides new geological evidence to support this hypothesis. The hydrothermal springs, where cracks on the seafloor let through iron-rich waters heated by magma, provided nutrients and energy to the early microbial communities. Metabolizing iron, sulfur and carbon dioxide to sustain growth and reproduction, the microbe’s waste products formed small nodules of hematite – an iron-oxide giving the rocks their red color – in the sediments. The hematite nodules are very similar to concretions still formed today by iron-eating microbes living on the seafloor, and they still contain traces of organic carbon.
Study lead author Dr. Dominic Papineau said: “Using many different lines of evidence, our study strongly suggests a number of different types of bacteria existed on Earth between 3.75 and 4.28 billion years ago.”
“This means life could have begun as little as 300 million years after Earth formed. In geological terms, this is quick—about one spin of the Sun around the galaxy.”
“These findings have implications for the possibility of extraterrestrial life. If life is relatively quick to emerge, given the right conditions, this increases the chance that life exists on other planets.”