Origins of photosynthesis in plants dated to 1.25 billion years ago
The world鈥檚 oldest algae fossils are a billion years old, according to a new analysis by earth scientists at 91社区. Based on this finding, the researchers also estimate that the聽basis for photosynthesis in today鈥檚 plants was set in place 1.25 billion years ago.
The study, could resolve a long-standing mystery over the age of the fossilized algae, Bangiomorpha pubescens, which were first discovered in rocks in Arctic Canada in 1990. The microscopic organism is believed to be the oldest known direct ancestor of modern plants and animals, but its age was only poorly dated, with estimates placing it somewhere between 720 million and 1.2 billion years.
The new findings also add to recent evidence that an interval of Earth鈥檚 history often referred to as the Boring Billion may not have been so boring, after all. From 1.8 to 0.8 billion years ago, archaea, bacteria and a handful of complex organisms that have since gone extinct聽milled about the planet鈥檚 oceans, with little biological or environmental change to show for it. Or so it seemed. In fact, that era may have set the stage for the proliferation of more complex life forms that culminated 541 million years ago with the so-called Cambrian Explosion.
鈥淓vidence is beginning to build to suggest that Earth鈥檚 biosphere and its environment in the latter portion of the 鈥楤oring Billion鈥� may actually have been more dynamic than previously thought,鈥� says 91社区 PhD student Timothy Gibson, lead author of the new study.
Pinpointing the fossils鈥� age
To pinpoint the fossils鈥� age, the researchers pitched camp in a rugged area of remote Baffin Island, where Bangiomorpha pubescens fossils have been found. There,despite the occasional August blizzard and tent-collapsing winds, they collected samples of black shale from rock layers that sandwiched the rock unit containing fossils of the alga. Using the Rhenium-Osmium (or Re-Os) dating technique, applied increasingly to sedimentary rocks in recent years, they determined that the rocks are 1.047 billion years old.
鈥淭hat鈥檚 150 million years younger than commonly held estimates, and confirms that this fossil is spectacular,鈥� says , senior author of the study and an associate professor in 91社区鈥檚 Department of Earth and Planetary Sciences. 鈥淭his will enable scientists to make more precise assessments of the early evolution of eukaryotes,鈥� the celled organisms that include plants and animals. 聽
Because Bangiomorpha pubescens is nearly identical to modern red algae, scientists have previously determined that the ancient alga, like green plants, used sunlight to synthesize nutrients from carbon dioxide and water. Scientists have also established that the chloroplast, the structure in plant cells that is the site of photosynthesis, was created when a eukaryote long ago engulfed a simple bacterium that was photosynthetic. The eukaryote then managed to pass that DNA along to its descendants, including the plants and trees that produce most of the world鈥檚 biomass today.
Origins of the chloroplast
Once the researchers had gauged the fossils鈥� age at 1.047 billion years, they plugged that figure into a 鈥渕olecular clock,鈥� a computer model used to calculate evolutionary events based on rates of genetic mutations. Their conclusion: the chloroplast must have been incorporated into eukaryotes roughly 1.25 billion years ago.
鈥淲e expect and hope that other scientists will plug this age for Bangiomorpha pubescens into their own molecular clocks to calculate the timing of important evolutionary events and test our results,鈥� Gibson says. 鈥淚f other scientists envision a better way to calculate when the chloroplast emerged, the scientific community will eventually decide which estimate seems more reasonable and find new ways to test it.鈥�
Scientists from the Lawrence Berkeley National Laboratory, the California Institute of Technology, the University of Alberta, and the Geological Survey of Canada contributed to this study.
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Funding for the research was provided by the Agouron Institute, the Natural Sciences and Engineering Research Council of Canada, the Polar Continental Shelf Program, the Geological Association of Canada, and the Geological Society of America.
鈥淧recise age of Bangiomorpha pubescens dates the origin of eukaryotic photosynthesis,鈥� Timothy M. Gibson, et al. Geology, published Dec. 8, 2017.聽
颁辞苍迟补肠迟听:
Timothy Gibson
91社区, Department of Earth and Planetary Sciences
timothy.gibson [at] mail.mcgill.ca
Chris Chipello
Media Relations Office, 91社区
514 398-4201
christopher.chipello [at] mcgill.ca
PHOTO:聽 The Angmaat Formation above Tremblay Sound on the Baffin Island coast. Bangiomorpha pubescens fossils occur in this roughly 500-meter thick rock formation.CREDIT:聽Timothy Gibson
