How in the world did life emerge on a planet composed only of simple chemical compounds? Scientists say they may have found part of the answer in a mineral that seems to act as an effective catalyst for the earliest organic processes.
Every organism on Earth, from the smallest bacterium to the blue whale, makes energy using the same biochemical pathway. Called the Krebs--or citric acid--cycle, this series of chemical steps converts carbohydrates, fats, and proteins into energy that powers cellular activities. To figure out how the Krebs cycle got started, scientists have been working backward to identify the nonorganic materials that originally helped set the cycle in motion.
Reporting in next week's Journal of the American Chemical Society, researchers at Harvard University say they may have found at least one of the original players. Called sphalerite, the compound is a mix of zinc and sulfur ejected from hydrothermal vents and known to have been plentiful in Earth's early seas. Geochemist and co-author Scot Martin says the team's new lab experiments show that when immersed in sterile water and exposed to sunlight, sphalerite can create three of the five basic organic chemicals necessary to start the Krebs cycle in relatively quick fashion. Further research is needed to isolate the other compound or compounds that could have produced the remaining two Krebs ingredients, he notes. If scientists can find their sources, then they will know that the five chemical foundations of the Krebs cycle were being manufactured easily and routinely in Earth's early oceans.
It's "elegant" research, says mineralogist Robert Hazen of the Carnegie Institution in Washington, D.C. The idea that sphalerite can catalyze three of the five Krebs cycle basic compounds all by itself is "an exciting result ... [that brings us] a lot closer to understanding the chemical origins of life."