The first signs of life emerged on Earth in the form of microbes about 4 billion years ago. While scientists are still determining exactly when and how these microbes appeared, it's clear that the emergence of life is intricately intertwined with the chemical and physical characteristics of early Earth.
"It is reasonable to suspect that life could have started differently - or not at all - if the early chemical characteristics of our planet were different," said Dustin Trail of the University of Rochester.
But what was Earth like billions of years ago, and what characteristics may have helped life to form? In a paper published in Science, Trail and Thomas McCollom of the University of Colorado Boulder reveal key information in the quest to find out. The U.S. National Science Foundation-supported research has important implications not only for discovering the origins of life but also in the search for life on other planets.
"We are now at an exciting time in which humankind is searching for life on other planets and moons, as well as in other planetary systems," Trail said. "But we still do not know how - or even when, really - life started on our own planet. Research like ours helps identify specific conditions and chemical pathways that could have supported the emergence of life, work which is certain to factor prominently into the search for life outside of our planet."
Research into life and its origins involves disciplines that include genomics, proteomics and metallomics, which explores the important role of metals in performing cellular functions. As life evolved the need for certain metals changed, but Trail and McCollom wanted to determine what metals may have been available when microbes first appeared billions of years ago.
They studied the composition and characteristics of fluids in the lithosphere - the outer layer of Earth, which includes the crust and upper mantle - billions of years ago. These lithospheric fluids are key pathways to transport dissolved parts of rocks and minerals between Earth's interior and the hydrothermal pools in its exterior where microbial life could have formed.
The researchers were surprised by what the model simulations indicated. Many origin-of-life researchers, for instance, consider copper a likely component in the chemistry that could have led to life. But Trail and McCollom did not find evidence that copper would have been abundant under the constraints in their analysis.
One metal they did test that may have been available in high concentrations was manganese. While it is rarely considered in origin-of-life scenarios, manganese helps the body form bones and assists enzymes in breaking down carbohydrates and cholesterol.
"Our research shows that metals like manganese may function as important links between the 'solid' earth and emerging biological systems at Earth's surface," Trail said.
Justin Lawrence, a program director in NSF's Division of Earth Sciences, added, "This study marks an important advance in our fundamental understanding of the early Earth. The link to modern systems and elements such as manganese may contribute to the emerging field of GeoHealth."
