PART 2 Over huge area of Siberia, enough lava erupted in a few thousand years to cover the lower 48 United States A KILOMETER DEEP. But as mindblowing as eruptions were, they only covered part of Russia--so lava itself couldn't have killed almost everything on the planet. 
It had to be the volcanic gases that came up out of the earth, especially CARBON DIOXIDE. Most ominously, these volcanoes had the misfortune of burning through one of the largest coal basins in the world, the Tunguska Basin.
By burning through this coal, the eruptions released something like 10,000 to 40,000 gigatons of carbon over thousands of years--a truly mind-boggling amount--and raised global temperatures an estimated 10-12 degrees C, acidified the oceans and starved them of oxygen
So, to recap: burning lots of coal 252 million years ago made it really hot, destroyed the oceans and almost sterilized the planet. This shouldn't sound encouraging to modern ears.
In the catastrophe's wake, reefs were largely replaced by bacterial slime, forests all but disappeared for 10 million years, and a whole menagerie of strange beasts on land disappeared as well. In total, ~90% of species died.
EXTINCTION 4: Amazingly, in the shadow of this Armageddon, life recovered. And 50 million years later at the end of the Triassic the world was enjoying a golden age of coral reef building, the emergence of icthyosaurs, mammals, turtles, and DINOSAURS.
But dinosaurs didn't rule yet. Life on land was instead dominated by a strange suite of CROCODILE relatives. And to inherit the world, dinosaurs first needed these strange crocs knocked off their perch. 201 million years ago they got their wish in the End-Triassic mass extinction
As North America pulled away from Africa, and Pangaea began to break apart, once again a gigantic swath of the planet turned inside out in an episode of mind-boggling volcanic eruptions.
These eruptions created the Central Atlantic Magmatic Province, a huge area (3 million square miles) of ancient lava and magma that today can be seen in imposing rock formations like the Palisades across from New York City.
As in the End-Permian and Late Devonian mass extinctions, it's thought that these eruptions drove extreme warming, ocean acidification and anoxia, killed the coral reefs, wiped out the crocs, and cleared the way for dinosaurs to take over the planet.
EXTINCTION 5: It's 135 million years later and now it's time for the showstopper--the most famous mass extinction of all time: The End-Cretaceous mass extinction 66 million years ago. The one that wiped out all the big dinosaurs (and tons of other cool stuff too).
In the late 70s Walter Alvarez, and his dad Luis, found a layer of asteroid (or comet) dust in these extinction layers in Italy (Jan Smit independently found the same signal in Spanish rocks).
And a decade later, paleontologists identified the buried 110 mile crater in Mexico that left all this extraterrestrial dust (a crater that had previously been described by oil geophysicists and which strangely explains some of the patterns of Mayan settlement (read the book))
The event is quite literally indescribable. As in, you couldn't have witnessed it. If you were in Alabama watching the asteroid touch down in Mexico you would have instantly gone blind and been set on fire...Then came the earthquakes and sonic booms and tsunamis.
And in the aftermath the rocks reentering the atmosphere from the impact might have broiled the planet in the hour after it hit. THEN the skies may have darkened with dust, cooling planet in years or decades afterwards, possibly even shutting down photosynthesis (prob not tho)
And by vaporizing a giant platform of carbonate rock in the Yucatan, the asteroid impact would have liberated gigatons of CO2 and caused global warming for 100,000 years as well (indeed, this has been seen in some isotope studies of the extinction).
Craziest thing about extinction though is that in India ANOTHER massive round of volcanism (enough to cover U.S. 600 FT DEEP) was going on at exact same time & recent studies show 70% of volcanism happened almost exctly when the asteroid hit! AND ASTEROID MAY HAVE KICKSTARTED IT!
As in other extinctions these volcanoes (The Deccan Traps) cld have contrib'd staggering amount of CO2 compounding already very bad situation. (Scientists still trying to untangle the relative impacts of the asteroid and volcanoes--though smart money still mostly on the asteroid)
So how abt #6? So far humans have had disastrous impact on enviro. Starting 1000s of yrs ago as we spread into new landmasses we wiped out tons of "ice age" & local fauna, destroyd incred amt of habitat thru farming & plow 2 US's of seafloor each yr w industrial fishing trawlers
Since the 80s a third of coral reefs have disappeared and, unless carbon emissions plummet to 0 in the next 2 decades or so, they're expected to completely collapse sometime after 2050. This is a catastophic impact that, in geological terms, is instantaneous as asteroid strike.
And yet, despite all the grim news...best estimates are that we've driven less than 1% of species extinct in the past ~400 years--a far cry from the 75-90% of these ancient apocalypses. That's the good news. There's still tons of biodiversity to save. We can still save the world.
HOWEVER, if we keep the current rate of extinctions up for a few more centuries we could actually be in the same conversation as the preposterous global catastrophes described above (which probably took many thousands of years to play out) [from Barnosky, 2011]
And all that's unless there are tipping points we don't know about, in which case it could all come crashing down sooner than that, especially as we acidify the oceans, destroy habitat and jackknife the climate.
In summary: global warming, and all its bad effects--driven by volcanic eruptions of CO2--likely played role in at least 4/5 worst things that have ever happened in the history of life on earth.
And, as far as we know, today we are emitting carbon dioxide at 10 times the rate of the WORST mass extinction of all time.
WE CAN STILL SAVE THE WORLD but we're currently meddling with some of the most ominous and unpredictable forces in earth history. FIN
WE CAN STILL SAVE THE WORLD but we're currently meddling with some of the most ominous and unpredictable forces in earth history. FIN
📸credits: Paleomaps--R. Blakey, Devonian fish--A. Atuchin, Flooded forest/t.rex/dinosaurs--D. Henderson, Ordovician--J. Agnew, Reefs--P. Copper, Ammonites--S. Stalenhag, Ice age--M. Anton, Triassic--W. Sillin
(small addendum: meant to include this entire paragraph)
Figures: Sahara striations--LeHeron, 2016; Plant Evolution--Algeo, 2010; P-T Temperatures--Penn et al 2018; CAMP map--Blackburn et al 2013; Acidification Scenarios--Hoegh-Guldberg 2007
