A trip to Shark Bay in Australia reveals what looks like a forest of mushrooms at low tide. These mounds of bacteria form stromatolites, the main communities of earth for over a billion years. Stromatolites lost out when animals evolved that ate them. So now stromatolites only live in water too salty or hot for those predators, as in Shark Bay or Yellowstone. So what do stromatolites have to do with black marble lines at Oregon Caves? They are the same, minus tides and about 240 million years. But of most interest is why they survived when apparently it wasn’t all that salty or hot. The answer may be why we breathe in and out every minute of our lives

Long before a meteor killed the dinosaurs, nearly all species and up to 99% of all individuals larger than a microbe suddenly died at the end of the Permian 251 million years ago. As in the end-Cretaceous disaster that killed the dinosaurs, only bacteria and fungi did well with so many corpses.


Extinctions increased before the end-Permian, as the world’s only continent had a harsh climate. Perhaps aided by vaporized rock from asteroid impacts, buildup of carbon dioxide from volcanoes increased temperatures enough to liberate marine methane “ices.” You may be most familiar with methane if you cook your food with it but it and carbon dioxide also comes from you know where. Both greenhouse gases heated the world by more than 10 degrees Fahrenheit, the hottest fever since the earth solidified. Hydrogen sulfide rose from seawater and in lungs turned to sulfuric acid, not the safest thing to swallow. Oxygen at sea level was about as concentrated as that found 20,000 feet above sea level today, which is why about the only surviving reptiles had huge lungs. So the stromatolites at Oregon Caves had a field day free from predators. Even their gooey remains weren’t disturbed by animals churning up the mud in search of food.

Although only climate can kill so many creatures on land and sea, we still don’t really know what caused life’s greatest disaster or most other mass extinctions. So we should be careful in changing our climate. And yes, there are sharks at Shark Bay. There are also very large and fast crocodiles that give a trip there a wholly different flavor than the usual seashore stroll.

Last updated: February 28, 2015

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