Volcanoes are giving asteroids a run for their money in the case of the biggest mass extinction event in Earth's history. The latest case has been made at the Geological Society of America meeting in Charlotte this week.
The researchers report they have found new evidence that the worst extinction event ever — the end-Permian mass extinction some 250 million years ago — was caused by a severe bout of global warming created by greenhouse gases released by a series of super-massive volcanic eruptions in Siberia. A similar case has been studied for several years now as a major contributor to the extinction of the dinosaurs 65 million years ago (the suspect gases at that time were released by gigantic Deccan Traps eruption in India).
I'm not going to analyze the science behind these hypotheses. But I do want to point out how curiously well mass extinction theories they mesh with popular thinking at any given time.
Right now there is a great deal of interest in climate change as a driver of major extinction events. Why? One reason is that we have a lot of people studying paleoclimates trying to learn as much as possible about the past so we can better understand our planet. Another reason is that the biggest threat to our planet and survival right now is anthropogenic climate change. But the story goes back much further than that.
In the 1980s climate change wasn't in the news yet and the asteroid impact hypothesis was gaining ground as the primary cause of at least the end-Cretaceous, dino-killing event. The scenario went like this: the asteroid crashed down and stirred up so much dust that Earth experienced a few dark years of what's called a nuclear winter. That winter disrupted the food chain and dinosaurs were wiped out. Of course, the important sociopolitical context for the asteroid impact hypothesis in the 1980s was the horrific "nuclear winter" that threatened humanity due to our proliferation of nuclear arms during the Cold War. However, this isn't the end of the story.
Before the 1980s, the idea of an asteroid impact would have been considered absurd. It went against a 19th century geological concept known as uniformitarianism or gradualism, in which the majority of Earth's changes happen very, very slowly over enormous periods of time. Gradualism was a dominant tenet of geological thinking almost to the end of the 20th century. But we still have one more twist to this tale.
Before gradualism took over, there was something called catastrophism, which was originally based on the Old Testament and considered the Earth young and the geological record we see today as the product of a series of divinely-inspired catastrophes (of course many religious fundamentalists still hold this view, although today it is blatantly anti-scientific). Once catastrophism was supplanted by science and gradualism, any scientist who talked about global catastrophes raining down from the heavens came off sounding like a throwback. That's why it was an uphill battle for hypotheses like asteroid impacts and supervolcanoes to get traction in the late 20th century.
Does this little historical review mean scientists are influenced by the political and popular events of their times? Of course! But that's okay. Scientists are only human.
Image credit: NASA