How and where did the first forms of life arise? These are the main questions driving research at the Institute of Molecular Evolution at Heinrich Heine University Düsseldorf (HHU). In a new publication in Science Advances, an international team led by Düsseldorf biologists uncovers pioneering insights into the network of chemical reactions that the very first cells used to make the building blocks of life and the energy sources they used to drive those reactions.

They retraced the origin of enzymes during life's earliest divergence into bacteria and archaea and found evidence for two independent origins of life for free-living cells.

If we could go back 4 billion years in time and watch as the first cells emerged on Earth, what would we see? "We would see two very different kinds of cells emerging, pioneer bacteria and pioneer archaea, making their first attempts at life outside the confines of a hydrothermal vent," says Natalia Mrnjavac, a biologist at the University of Düsseldorf and lead author of the new publication.

There, Mrnjavac and an international team of scientists report investigations of genomes, protein structures and chemical reactions that probe the earliest phases of microbial evolution before there were free-living cells.

"These comparisons are giving us unprecedented insights into the phase of evolution when metabolism catalyzed by enzymes was arising from spontaneous reactions catalyzed by metals in the Earth's crust," says Düsseldorf biologist William Martin, senior author of the study.