Diamonds in the Rough
Looking for Life in Rocks
Anyone who knows a trilobite from an ammonite can tell you that the history of early life is a book written in rock.
|400 million-year-old trilobite fossil. Trilobites dominated the as a marine fauna during the Cambrian Period. Charles Darwin noted: "Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare? Yet these relations are of the highest importance, for they determine the present welfare, and, as I believe, the future success and modification of every inhabitant of this world."
According to SETI Institute scientist Friedemann Freund, chapter one and perhaps chapter two may have been written at least in part, by the rocks themselves. Common rocks, he explains, such as gabbro and granite carry a payload of complex chemistry that may have played a dynamic role in life’s origin, and the co-evolution of life and Earth’s oxygen-rich atmosphere.
Freund first began studying this premise twelve years ago at NASA Ames Research Center as a SETI Institute principal investigator researching life’s origins. While other exobiologists (as astrobiologists were then known) looked towards comets as potential delivery vehicles of life’s basic materials, or at warm little ponds as assembly sites for life, Freund was intrigued by the interesting organic chemistry he found taking place in the misalignments and displacements in rock crystals.
|A crystal can grow, reach equilibrium, and even move in response to stimuli, but lacks what commonly would be thought of as a biological nervous system.
Image Credit: National Ignition Facility Programs
Most of the "interesting" properties of minerals and rocks, Freund contends, are determined by their imperfections and impurities. Rubies, sapphires and other gems, for example, derive their colors from chemical impurities. Early in his career as a crystallographer, Freund wondered about the minerals that incorporate molecules of the common gases – water, carbon dioxide, nitrogen – what happens to these gas molecules once they are lodged within the dense crystal matrix?
This "ignored" area of geophysics presented huge difficulties. The concentrations of the former gas molecules within the crystals are small (mostly less than 100 parts per million). They are not easy to detect.
Freund embraced the challenge, developing some novel and highly precise measuring techniques. His findings were astounding and in many ways counter-intuitive. Minerals, he discovered, are chemical factories where carbon, nitrogen, oxygen and hydrogen – the consequence of the incorporation of water, carbon dioxide, nitrogen – can assemble into complex organic molecules, and at the same time form highly reactive peroxy groups.
The observation of such complex organic molecules, or precursors thereof, led to the idea that the weathering of rocks might release significant amounts of organic material. Assuming that the weathering rate on the barren land surfaces of the early Earth was comparable to what it is today, about 10 billion tons of rock would dissolve every year, pointing at the exciting possibility that a payload of complex organic molecules would have liberated perhaps as much as 1 million tons every year. At the same time, the peroxy groups would have turned into hydrogen peroxide and initiated a slow but inextricable process of planetary oxidation.
Under the SETI Institute’s NASA Astrobiology grant Freund will be focusing on the peroxy chemistry of rocks. A few years ago, Freund wondered whether a slow trickle of hydrogen peroxide that would be released at the rock-water interfaces, where early microbial colonies were likely to dwell, could have stimulated the development of biochemical defenses against oxygen in primitive microbes on the otherwise anoxic early Earth.
"Perhaps," Freund explains, "organisms exposed to a constant trickle of hydrogen peroxide in their immediate environment were forced to develop enzymes which were able to protect them from oxygen (oxygen is lethal to primitive life) long before there was an oxygenated atmosphere, but no one knew why." Enter Dr. Lynn Rothschild, a NASA Ames microbiologist who worked down the hall from Freund.
"I knew Lynn and always enjoyed talking to her," says Freund, "I would ‘bug’ her with questions about biology."
A few years ago, Freund approached her with the idea that the presence of peroxy in rocks could have produced a steady low-level exposure of early organisms to the highly reactive hydrogen peroxide. If such an oxygenating source were present on early Earth it would have far-reaching consequences for the "oxygen transition" of the atmosphere. Rothschild said, "let’s talk about this later." And after a year of mulling it over, she came to agree that the hypothesis sounded plausible, was interesting and should be testable. Today, the NASA microbiologist and the SETI-Institute physicist are collaborating on a project that examines the peroxy effects on microbial life.
If there is a downside to the rock research–beyond the challenge of explaining electrochemistry to a lay public–it is perhaps in the cumbersome nature of the material under study. Freund obtains much of his material from a San Jose supplier who deals in monuments and cemetery markers. The stone must be cut and moved, and the handling is often the greatest cost of research. Last year, Freund recalls, he was given a boulder from "a beautiful piece of the Earth’s mantle" uplifted by the Cascade Mountains of Washington state. The gift weighed 15 tons.
Another rock in the road of life? Perhaps, but also a world of discovery.
Related Web Pages
Digital Zookeepers Take a Census
Biological Diversity: Fact or Artifact?
Evolution’s Slow Recovery
New Species and Understanding Earth
The Paleobiology Database
NASA Workshop on Biodiversity
University of California Museum of Paleontology
Entropy and Evolution
What is Life?