The Mass Extinction that Left the Dinosaurs Standing
|Radiolaria shells. The sharp decline in radiolaria was the focus of the new research.|
Credit: Microscopy UK
A mass extinction about 200 million years ago, which destroyed at least half of the species on Earth, happened very quickly and is demonstrated in the fossil record by the collapse of one-celled organisms called protists, according to new research led by a University of Washington paleontologist.
"Something suddenly killed off more than 50 percent of all species on Earth, and that led to the age of dinosaurs," said Peter Ward, a UW Earth and space sciences professor.
Evidence indicates the massive die-off was linked with an abrupt drop in productivity, the rate at which inorganic carbon is turned into organic carbon through processes such as photosynthesis. The waning productivity coincided with a sharp decline in radiolaria (included among protists), which was the focus of the new research. One example of productivity, Ward explained, occurs in the spring when fertilizer washes into waterways and triggers large algae blooms. The processes at work in that scenario were reversed 200 million years ago, he said.
There is no definitive evidence yet on what caused the demise of so many species, Ward said. However, the suddenness of the event is similar to two better-known mass extinctions – one 250 million years ago at the end of the Permian period that killed some 90 percent of all species, the other 65 million years ago at the end of the Cretaceous period that sent the dinosaurs into oblivion.
The extinction 200 million years ago, at the boundary between the Triassic and Jurassic periods, killed the last of the mammal-like reptiles that once roamed the Earth and left mainly dinosaurs, Ward said. That extinction happened in less than 10,000 years, in the blink of an eye, geologically speaking.
|A plot of data on mass extinctions. Dinosaurs survived the mass extinction that took place about 200 million years ago.|
Credit: University of Chicago
Ward is the lead author on a paper detailing the evidence, published in the May 11 edition of the journal Science. Others participating in the research are James Haggart and Howard Tipper of the Geological Survey of Canada in Vancouver, British Columbia; Elizabeth Carter, a researcher at Oregon’s Portland State University; David Wilbur, a UW oceanography research scientist; and Tom Evans, a UW junior in chemistry and Earth and space sciences.
The evidence from the extinction was gathered at two sites in the Queen Charlotte Islands, off Canada’s British Columbia coast.
"These sites are among the most remote places in the world," Ward said. "There are no roads anywhere close by. The forests are virgin old growth, and the wave action is such that you can’t get there by boat."
Samples from a spot called Kennecott Point, in the northern Queen Charlottes, and from Kunga Island, about 100 miles to the southeast, showed a sharp decline in the presence of organic carbon, even at places where levels of inorganic carbon rose. The organic carbon decline correlated with the decline of radiolarians, one-celled organisms that serve as a food source for a number of marine species.
"These provide the best record of how nasty the extinction was at this boundary," Ward said.
|This animation shows the supercontinent Pangea breaking up. The animation begins early in the Mesozoic Era, during the Triassic Period, showing the motion of the continents to their present positions.|
The mass extinction 200 million years ago occurred just before the breakup of Pangea, which contained all the land on Earth in one supercontinent. At the time, the Queen Charlotte Islands – which now lie between 52 and 54 degrees north latitude – were probably on the equator or in the southern hemisphere, Ward said.
"These are tropical fossils. There are many kinds of fossils in these rocks," he said.
And they tell a story of a calamity that came on with stunning swiftness.
"This is the first time ever that we can see how sudden this event was," he said. "It was very quick, not a long protracted episode."
Ward now has done research on the last three of the Earth’s mass extinctions (scientists know of five) and has found that each happened quite quickly.
Bolstered by a recent astrobiology grant from the National Aeronautics and Space Administration, he plans to lead researchers back to the Queen Charlottes this summer to look for more clues in the Triassic-Jurassic extinction, including potential causes.