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Gibson and his colleagues did that to estimate that the first photosynthetic eukaryote evolved around 1.25 billion years ago.Roger says the new, more precise age for Bangiomorpha measured by Gibson, Halverson and their colleagues is "definitely important — but it doesn't completely solve the problem." He said he still finds it "very concerning" that no other fossils of recognizable complex organisms besides Bangiomorpha older than 800 million years have been found to date.

But the fact that its age could have been anywhere in a 500-million year span led to some controversy.Some scientists' calculations based on DNA evidence suggested red algae couldn't have existed 1.2 billion years ago.Working up there was a "dream come true" for Gibson: "It's a magical place I've wanted to go for a long time." For four summers, he and a small team helicoptered in to sites between Pond Inlet and Arctic Bay.They camped on the tundra in lightweight tents at the tops of sea cliffs to avoid polar bears, then scrambled down to collect samples with simple rock hammers.He named it: The fossil was extraordinary because it was found in a rock formation up to 1.2 billion years old and appeared to be the oldest multicellular organism that was a recognizable eukaryote — the group of complex organisms that include plants, animals and fungi — rather than a colony of microbes living together.

"It is an extremely important fossil and has been quite controversial," said Andrew Roger, a molecular biologist at Dalhousie University who was not involved in the new study.Once back at the lab, the researchers measured the amount of radioactive rhenium-187, a rare radioactive isotope found in seawater that accumulates in organic matter and decays to osmium-187.Very little osmium-187 is found naturally in rocks.He is presently employed in the Space & Atmospheric Sciences Group at the Los Alamos National Laboratory.Radiometric dating--the process of determining the age of rocks from the decay of their radioactive elements--has been in widespread use for over half a century.Molecular clock estimates of events in early evolution often have extremely large error bars — sometimes spanning hundreds of millions of years — partly because the fossil record from that time is so incomplete, he added.