Dinosaurs Survived One Mass Extinction

May 10, 2001 -- The dinosaurs were wiped outby an asteroid that smacked the Earth 65 million years ago, butthey survived another cataclysmic event — perhaps anotherasteroid impact — that snuffed out 80 percent of all speciesabout 200 million years ago, scientists said today.

By studying the fate of a type of marine plankton,single-celled organisms called Radiolaria, researchers foundthat the mass extinction was a sudden event, not the prolongeddie-off that experts previously had thought. The extinctionoccurred at the boundary between the Triassic and Jurassicperiods during the Mesozoic era.

The event provided the death knell for most species andhelped crown the dinosaurs, which arose earlier in theTriassic, as the rulers of the Earth, said Peter Ward, aUniversity of Washington paleontologist who led the study.

Ward said this calamity had tremendous similarities to twoof the other five mass extinctions that have ravaged Earth overthe past 500 million years. Like those, Ward said it appearsthis mass extinction was caused by a giant rock from space.

"We know now that asteroid impact can cause rapidextinction," Ward said in an interview. "It may not be anasteroid. But if it isn't an asteroid, it acts like anasteroid, put it that way."

Wiped Out in a Second?

Most scientists believe an asteroid strike caused the massextinction at the end of the Cretaceous period that killed thedinosaurs and ushered in the age of mammals. In February,scientists presented evidence that an asteroid or comet impactalso caused the even bigger extinction at the boundary betweenthe Permian and Triassic periods 250 million years ago.

Ward's team gathered evidence about the extinction 199.6million years ago at two remote sites in the Queen CharlotteIslands off Canada's British Columbia coast, examining fossilsamples indicating a collapse of the plankton population.

The researchers found an abrupt drop in the rate at whichinorganic carbon was turned into organic carbon by life formsthrough processes such as photosynthesis.

The organic carbon decline coincided with the disappearanceof more than 50 species of radiolarians, which served as a foodsource for numerous marine species and whose disappearance wasan indicator of a major biological crisis.

The study was published in the journal Science.

Ward said the research indicated it took less than 10,000years for the mass extinction to unfold. It could have takenplace even more quickly — perhaps in an instant, he added.

"This thing was real fast," Ward said.

At the time, most dinosaurs were relatively small, and theywere locked in a survival-of-the-fittest battle with otherwell-adapted animals, including the mammal-like reptiles — thebiggest of which were among the major herbivores of their day.

"These suckers are huge, they're hulking," Ward said.

But the mammal-like reptiles — whose earlier forms gaverise to the first true mammals — perished in the calamity.

"One of the great mysteries has been … why would thesecreatures, which are seemingly better adapted for eating avariety of plant sources, die out and the dinosaurs not? Andthe answer is: Mass extinction doesn't give a hoot about youradaptations for everyday life. There's a lottery involved, forwhatever reason," Ward said.

Also nearly wiped off the planet were the ammonoids — marine predators that resembled a giant squid in coiled coneshell.

Death From the Sky

Ward said there are ongoing studies to try to confirm anasteroid as the cause. Ward said he has found evidence oflittle carbon molecules called buckminsterfullerenes — orbuckyballs — that hint at a space rock as the culprit.

He said a massive crater in Quebec called the Manicouaganstructure, which measures 60 miles (100 km) wide, could be theimpact site. The crater has been dated to 214 million yearsago, but Ward said the date may be too old.

Ward said alternative theories include an explosion of anearby star that could have blown off the Earth atmosphere'sozone layer and sent temperatures soaring, or massive volcanicactivity, possibly related to the breakup of the archaicsuper-continent known as Pangea.

Scientists know very little about the mass extinctions thattook place 350 million and 420 million years ago, Ward said.