Last week, we looked at prehistory's five great extinction events and suggested that extraterrestrial sources may be the binding threads in our planet's violent tapestry of death. We briefly outlined extinction events 1 through 4. This week, we conclude with extinctions 4 and 5. Are there any cosmic smoking guns here?
•Extinction 4-The Triassic-Jurassic extinction event occurred 205 million years ago. At the T-J boundary, nearly 48 percent of all zoological and botanical genera-terrestrial and marine life-went extinct.
Most archosaurs-except the lucky dinosaurs- and most therapsids, which include mammals and their immediate evolutionary ancestors, died out. Even many large amphibians became extinct. The result opened up the environment to the surviving dinosaurs. (Of course, the dinosaurs own turn to face the Darwinian firing squad will come at extinction 5.)
Only a few large amphibians emerged from extinction 4 and managed to survive, barely, into the Cretaceous. For example, the giant, lumbering amphibian known as Koolasuchus-one of the paleo stars of the 1999 BBC-TV mini-series "Walking with Dinosaurs"-became the lone survivor of the now utterly vanished biological order Temnospondyli.
As with earlier extinctions, an extraterrestrial agent may have had a hand in the T-J megadeaths, but we're not 100 percent certain.
Could the giant, 62-mile-wide ring-like Manicouagan Reservoir feature in central Quebec be the smoking gun? Maybe, but it's a big maybe.
The now highly eroded, water-filled impact basin probably was excavated by a rocky asteroid three miles in diameter. The scale of the Manicouagan impact should have produced planetwide fires and dust clouds with impact debris raining down for thousands of square miles. Yet, many researchers now believe the crater was formed 12 million years before extinction 4. Ok, if Manicougan isn't the culprit, then why didn't planetwide extinctions occur at the time of that impact? More geological investigations are needed.