Stromatolites surprise researchers

Living fossils of the sea are dominated by oxygen-consuming microbes

Stromatolites University of Miami
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Where did life on earth originate? This question is still not clear. For the first time American scientists have begun to search for "fingerprints" of primeval microbial life in special oceanic reefs. Already, the study on the so-called Stromatoliten brought some surprises, as a publication in the journal "Geology" shows.

The modern representatives of stromatolites are living examples of one of the oldest and most widespread marine ecosystems. Its origin dates back over three billion years. Over 80 percent of the earth's history was dominated by the massive reefs of the primeval oceans. "Builders" of these reefs are not coral but microorganisms. They bind sand and calcium carbonate particles, creating the typical stratified calcareous hills over time.

Scientists led by Miriam Andres of the University of Miami have now developed a new approach to better study the formation and composition of stromatolites. "The motivation for this study is the lack of direct evidence of microbial activity in primeval stromatolites, " explains Andres. "Stable isotopes have proven to be a powerful tool to 'fingerprint' microbial metabolic pathways and better understand sedimentary structures in geological discoveries."

Oxygenating microbes dominate

In fact, the study has already revealed some surprising facts: Previously, it was assumed that predominantly autotrophic microbes - that is, microorganisms that carry out photosynthesis - were and are responsible for the formation of stromatolites. But Andres and her colleagues had to learn better: "We knew that the stromatolite ecosystem is dominated by photosynthetic cyanobacteria and expected to see this also reflected in a corresponding carbon isotope ratio. Instead, we found the exact opposite, "says Andres.

In fact, heterotrophic, oxygen-consuming microbes dominated over the photosynthetic pathways. "We still do not understand how stromatolites actually calcify, " explains the researcher. "This information will be the key to understanding how organisms make up skeletons and when that process first began." Ad

(University of Miami, November 20, 2006 - NPO)