Now here’s a list from 2011, by a group of researchers led by Anthony Barnosky, showing possible causes for those mass extinctions. These are only some of the many scientific ideas out there about causes.
Table 1: The ‘Big Five’ mass extinction events (Barnosky et al.)
Myr = million years. Kyr = thousand years.
|The Ordovician event. Ended ~443 Myr ago; within 3.3 to 1.9 Myr 57% of genera were lost, an estimated 86% of species.||Onset of alternating glacial and interglacial episodes; repeated marine transgressions and regressions. Uplift and weathering of the Appalachians affecting atmospheric and ocean chemistry. Sequestration of CO2.|
|The Devonian event. Ended ~359 Myr ago; within 29 to 2 Myr 35% of genera were lost, an estimated 75% of species.||Global cooling (followed by global warming), possibly tied to the diversification of land plants, with associated weathering, paedogenesis, and the drawdown of global CO2. Evidence for widespread deep-water anoxia and the spread of anoxic waters by transgressions. Timing and importance of bolide impacts still debated.|
|The Permian event. Ended ~251 Myr ago; within 2.8 Myr to 160 Kyr 56% of genera were lost, an estimated 96% of species.||Siberian volcanism. Global warming. Spread of deep marine anoxic waters. Elevated H2S and CO2 concentrations in both marine and terrestrial realms. Ocean acidification. Evidence for a bolide impact still debated.|
|The Triassic event. Ended ~200 Myr ago; within 8.3 Myr to 600 Kyr 47% of genera were lost, an estimated 80% of species.||Activity in the Central Atlantic Magmatic Province (CAMP) thought to have elevated atmospheric CO2 levels, which increased global temperatures and led to a calcification crisis in the world oceans.|
|The Cretaceous event. Ended ~65 Myr ago; within 2.5 Myr to less than a year 40% of genera were lost, an estimated 76% of species.||A bolide impact in the Yucatán is thought to have led to a global cataclysm and caused rapid cooling. Preceding the impact, biota may have been declining owing to a variety of causes: Deccan volcanism contemporaneous with global warming; tectonic uplift altering biogeography and accelerating erosion, potentially contributing to ocean eutrophication and anoxic episodes. CO2 spike just before extinction, drop during extinction.|
Those explanations mostly involve environmental concerns. That’s a subject ripe for parody these days.
Having been blinded by science, I have no idea whether or not those are good explanations. I still want to know about mass extinction, though. Here is what it all looks to me now.
Disaster sells, so today we’re overloaded with dire news about the environmental catastrophe that’s just around the corner if we don’t change this or do that…and then tomorrow there’s a new study saying, no, the catastrophe will happen if we don’t do things this way.
It’s confusing, but fortunately global nuclear war is no longer a threat. We can safely turn our attention to…
Wait a minute. The nuclear threat did not vanish along with the USSR in the early 1990s. Nuclear winter is just not trendy to write about now, after the Cold War.
Since headlines must still be written, and because human nature will always need an ideology to fight over, I think we’ve turned to that other big global concern that arose in the mid-20th century.
The present is the key to the way we see the past
When the threat of imminent nuclear war hung over us in the 20th century, scientists were talking about impacts, since one was definitely associated with the K/T extinction and could have caused a nuclear winter (minus the radiation). Today’s science news covers mass extinctions caused by ice ages and global warming, the rise and fall of seas, greenhouse gases, atmospheric and oceanic chemistry, and massive volcanic eruptions
Is it a coincidence that nowadays journalists write about global warming, climate change, and supervolcanoes? I think not, though it’s a chicken-egg problem if you look at it too closely.
There is something very important, however, that’s been missing from all the headlines and science reports on mass extinctions that I have seen.
Supposedly a flap of a seagull’s wings can alter weather forever.
This “butterfly effect” has operated down through geologic time. There’s no way to see it in the fossil record.
We can’t, therefore, ever really know much about a mass extinction or the recovery of life on Earth after such an event.
However, since it’s human nature to attempt the impossible, scientists are out there collecting data and interpreting it as seems best to them. The point I’m trying to make here is that, as impressive as it all is, anything they come up with can only be a work of art, no matter how precisely drawn and objective it may seem to a layperson or even to other scientists.
It will never accurately explain the actual events.
What’s a layperson to do?
Today we have huge stores of skepticism in places like The Onion. Back in the 19th century, they were fortunate enough to have Mark Twain.
One of his most famous quotes came out of the scientific ideological conflict at that time between catastrophism and gradualism.
In Life on the Mississippi, after telling the reader in great detail how difficult it was to learn the vast and ever-changing Mississippi River – a figure of chaos if ever I saw a figure – and how vital it was for a steamboat pilot to master this knowledge, Twain discussed the river’s habit of shortening itself by cutting off some of its meandering loops.
Then he said:
In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oolitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-rod.
And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three-quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
One does indeed.
That’s something to keep in mind as we monitor science news and try to make sense out of the competing calls for our attention and money.
Monitor it we should. A massive global catastrophe could result from a bolide impact or a huge volcanic eruption. More than 90% of life on Earth appears to have died off during the Permian mass extinction – why?
We do need answers to the questions I raised last time:
- What do we need to do, if anything?
- How will the next extinction happen?
- Is it happening now?
- Which species are most vulnerable?
- Where should we focus our research?
Right now, there is wholesale conjecture about all of these things, very few facts.
We have cycled through the nuclear-winter/impact fashion and are currently wrapped up in environmental-science/environmental-disaster. What will the next trend be?
I’d like to see something akin to the old belief-in-the-future/can-do thinking throughout all levels of society and science that put men on the Moon. But that would be a step backwards.
As the disaster-haunted Boomers fade away, maybe thinking will turn toward the new and unpredictable, something like but more realistic than the old hopeful attitudes of the 1950s and 1960s.
That might be helped along by a desirable extinction of the idea (PDF) that any society can spend more than it earns and still get somewhere.
Of course, chaos will certainly intervene. Humanity will be in crisis, but come what may, eventually we’ll come up with something new (or something so old it might as well be new).
Life will find a way, as it always has and probably always will. Wouldn’t it be great if it could somehow involve dinosaurs?
Front page image source: Mass Extinctions. G. H. Rieke, Arizona State University
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