By most current estimates microbial life has populated Earth for over 3.5 billion years. While we can trace the evolution of life using paleontology and phylogenetic techniques, the chemical events that gave rise to pioneer life forms remain unknown, and related research efforts comprise a controversial field of scientific research. In a paper published today (16 May 2013) in Nature, DCO scientists are contributing to the debate with new results on the age of deep fluids in crystalline rocks that constitute some of the deepest habitable zones on Earth .
In 1953, Nobel Prize-winning chemist Harold Urey and his then graduate student Stanley Miller published a seminal experiment: They showed that in their laboratory-simulated conditions of a young Earth, an electric spark could promote chemical reactions that would form some of the molecular building blocks of life, including amino acids and carbohydrates . Thus, the “primordial soup” theory was born, in which surface chemistry, heavily reliant on energy from the Sun, was the driving force of life’s beginning.
With subsequent advances in technology and human exploration, however, it has become clear that life can thrive in places where sunlight and lightning strikes are nonexistent . Investigations into this phenomenon have lead many geologists to wonder if life might actually have arisen in a very different way from Urey and Miller’s dramatic demonstration. Perhaps chemical processes, driven by the thermal energy of a deep volcanic vent or the chemical energy of serpentinization reactions, deep underground or on the seafloor, might represent a more plausible explanation for the origin of life on Earth and other planets.
“At the time life arose on Earth, the planet’s surface was exposed to high levels of UV light and still threatened by bombardment from extraterrestrial debris. It is conceivable that life arose not in a warm little pond, but sheltered in a warm little fracture below the surface of the crust, or in the deep oceans, protected from tumultuous events on the surface,” says DCO scientist and article co-author Barbara Sherwood Lollar.
In order to address these complex and controversial hypotheses, Sherwood Lollar and fellow DCO researcher Chris Ballentine and their colleagues turned to clues hidden 2.4 km below the surface of 2.7 billion year-old Precambrian Shield rocks in Timmins, Ontario, Canada (see attached video for a look at how these samples were collected). Fluid inclusions in crystalline rocks have long been studied for the information they contain about the composition of the Archean atmosphere, as well as how such fluids were involved in the formation of gold and other ore deposits found in these rocks worldwide. By analyzing the chemical composition of these fluids, the researchers provided startling evidence that fluids and gases naturally flowing out of these rocks, at flow-rates of greater than one liter per minute, are as ancient as the rocks themselves. Moreover, the chemical characteristics of these hydrogen- and methane-rich fluids, and the nature of the water-rock reactions that control its composition, are similar to those deep ocean environments that have been suggested as the settings for life's ancient origins.
“Our teams at Manchester and Toronto have partnered for years in investigations of hydrocarbon gases in sedimentary basin systems. This was an exciting opportunity to extend the noble gas insights to the unique challenges of the deep carbon cycle,” says Ballentine.
For more from Chris Ballentine, listen to the Nature Podcast here.
So if such conditions exist miles below the surface of Earth, and have the potential to foster and sustain primitive life, planets such as Mars may have once played host to subterranean life. Perhaps in both our quest to understand life on Earth, and our relentless search for extraterrestrial biology, we should look a little deeper.
“While the life questions raised by our work are incredibly exciting, the ground-breaking techniques we have developed at Manchester to date ancient waters also provide a start for calculating how fast methane gas is produced in ancient rock systems globally; as well as developing a technique that we can apply to characterizing old deep groundwater that may be a safe place to sequester carbon dioxide.”
Photo Credit: Buried life: Gas that bubbles out of the floor in a deep mine has a chemical composition that can provide the food source for microbes living in deep ancient fluids underground. J Telling U of Toronto (2009)