Carrine Blank, Ph.D., Washington University assistant professor of geomicrobiology in the Department of Earth & Planetary Sciences in Arts & Sciences, studying Cyanobacteria ?bacteria that use light, water, and carbon dioxide to produce oxygen and biomass ?has concluded that these species got their start on Earth in freshwater systems on continents and gradually evolved to exist in brackish water environments, then higher salt ones, marine and hyper saline (salt crust) environments.
Cyanobacteria are organisms that gave rise to chloroplasts, the oxygen factory in plant cells. A half billion years ago Cyanobacteria predated more complex organisms like multi-cellular plants and functioned in a world where the oxygen level of the biosphere was much less than it is today. Over their very long life span, Cyanobacteria have evolved a system to survive a gradually increasing oxidizing environment, making them of interest to a broad range of researchers.
Blank is able to draw her hypothesis from family trees she is drawing of Cyanobacteria. Her observations are likely to incite debate among biologists and geologists studying one of Earth's most controversial eras ?approximately 2.1 billion years ago, when cyanobacteria first arose on the Earth. This was a time when the Earth's atmosphere had an incredible, mysterious and inexplicable rise in oxygen, from extremely low levels to 10 percent of what it is today. There were three ?some say four ?global glaciations, and the fossil record reflects a major shift in the number of organisms metabolizing sulfur and a major shift in carbon cycling.
"The question is: Why?" said Blank. "My contribution is the attempt to find evolutionary explanations for these major changes. There were lots of evo
Source:Washington University in St. Louis