|
For the first three-quarters of its history, Earth's biosphere consisted exclusively of microbial life. Most of this period was dominated by photosynthetic microbial mats, highly complex and organized communities of microorganisms that once covered the Earth. For two billion years, these mats were the primary biologic agents of global environmental change (for example, the oxygenation of the atmosphere) and the crucible for evolution of the complex macroscopic life forms we know today. Ames' Early Microbial Ecosystems Research Group studies the biology, chemistry, and geology of closely related modern microbial mats in order to better understand the important role played by their ancient counterparts.
A key focus is to understand how the chemistry of the mat influences, and is influenced by, the collective activities of the constituent bacteria. The sunlit surface layer of the mat harbors the highest population of active bacteria, is the most productive, and has the most direct interaction with the outside environment. Within this layer, concentrations of two gaseous products of microbial metabolism, hydrogen and carbon monoxide, vary in dramatic fashion during the course of one day (as shown in figure 1). The light-driven liberation of carbon monoxide has not been previously observed in mat communities. Given the widespread distribution of mats on early Earth, this light-driven liberation of carbon monoxide could have represented a significant but unrecognized contribution to the ancient atmosphere. Hydrogen concentrations in the mat vary by a factor of 10,000 or more during one day/night cycle. This variation is much greater than the variation that the Earth's surface environment on the whole has experienced during its entire history.
This variation in hydrogen is especially important in the context of the microbiology and chemistry of the mat. Many of the bacteria in the mat utilize hydrogen as an essential means of transferring chemical energy and "information" to one another. The dramatic daily variations in hydrogen may extensively influence the way in which these organisms interact and function as a collective whole. An important key to global change in the ancient environment, and to half of the evolution of life on Earth, may thus lie in the roller-coaster chemistry of microbial mats.
Point of Contact: T. Hoehler
(650) 604-1355
thoehler@mail.arc.nasa.gov
Back To Top
Previous Paper
Return to Exobiology
Next Paper |
|
Fig. 1. Light intensity (a), carbon monoxide concentration (b), and hydrogen concentration (c) at the surface of a microbial mat from Baja, Mexico, during the course of one diel (24-hour day/night cycle). These graphs illustrate the dramatic light-driven chemistry generated by bacteria within the microbial mat. The chemical environment shown here experiences a greatly more substantial shift in conditions over a few hours than the Earth's atmosphere has during its entire history.
|
|
