The Mass Extinction that Left the Dinosaurs Standing
"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.
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.
"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.