Mass Extinctions Part 3: The Beginning of a New World

A favourite trope of many film-makers is the asteroid impact – think Armageddeon or Deep Impact. Typically, we’d have the intrepid protagonists devise some ingenious plot to deflect the asteroid – or it would land, torching the Earth as we knew it and transforming it into a flaming hellscape.

As with all things, reality tends to lie in between. When the dinosaurs looked up and saw the asteroid that would bring about the end of their era streaking across the sky, chances are most of them wouldn’t have felt the impact until much later.

Speaking of dinosaurs, how did that resilient little branch we call “birds” end up thriving after the dust settled?

Today, we’ll be tackling the Triassic extinction, more accurately the Triassic-Jurassic extinction, as well as the poster child of all catastrophes: the K-T extinction (or K-Pg extinction, rather) that robbed us of the dinosaurs. Strap in and get ready for the third instalment of the Mass Extinctions series!

Triassic

The Triassic extinction seems like something out of a bad nightmare – brought about by the eruption of the Central Atlantic Magmatic Province (or CAMP), the most extensive continental Large Igneous Province (LIP) known to man. For those who haven’t seen them in our previous articles, LIPs are areas where magma from the lower levels of the Earth’s crust or mantle rise up through the ground, producing areas with catastrophic levels of volcanic activity.

The CAMP was formed before the breakup of Pangaea, during that brief instant where all of Earth’s continental landmass had coalesced into one single continent. Its formation was marked by a large upwelling of basalt (a rock derived from rapidly cooling lava) and huge volcanic activity.  Evidence of this was submerged when Pangaea splintered apart and the Atlantic ocean formed (the same one we have today), but even now the evidence of the CAMP’s presence was clear due to the characteristic formations of rock left behind under the ocean.

Using evidence from huge disturbances in the carbon isotope record, it has now been demonstrated that the CAMP’s activity 200 million years ago coincides very closely (within the span of a million years) with the extinction pulses of the Triassic extinction.

During these pulses, huge amounts of carbon dioxide and other greenhouse gases were released into the air at once – a single such pulse could be equivalent to our projected total greenhouse gas emissions for the entire 21st century. The global warming from each eruption would have been on a scale that is difficult to quantify, let alone imagine.

A familiar story now begins here, and we begin to see that though history may not repeat itself, it does rhyme. With so much volcanic activity, the concentration of oxygen in the seas begins to drop as they acidify, leading to anoxia, or a state of low oxygen in the water. With evidence of marine sulphide-processing bacteria flourishing during this period, we can also guess that euxinia (dropping oxygen levels paired with toxic sulphides emitted from the volcanoes) took place at the same time. Apart from sulphides, other toxins such as mercury were released in vast amounts.

Beyond this, though, a second deadly factor arose – global cooling. While greenhouse gases trapped heat on Earth at the onset of each eruption and lay the equivalent of thick thermal blankets over the surface, many gases such as nitrogen dioxide were released in CAMP activity that were opaque and blotted out the sun.

While heat ravaged some populations with fires and suffocating acidification, others were plunged into darkness, with photosynthesis ceasing and everything above that in the food chain perishing without anything to eat.

Beyond this alone, there is evidence that ozone depletion occurred during the extinction, resulting in a higher rate of deleterious mutations and DNA damage that could have contributed to increased extinction rates during the Triassic-Jurassic boundary.

Interestingly enough, there is some evidence that marine species were not as severely impacted as terrestrial species during the extinction despite the massive changes occurring in the marine environment. Furthermore, they quickly recovered and many that had briefly disappeared such as giant bivalves (think massive clams) reappeared shortly after. On the other hand, much terrestrial fauna such as primitive amphibians and reptiles vanished forever, leaving many niches open for the taking.

One group of animals took the chance to diversify rapidly, filling up every ecosystem, and radiating out to form a wide range of species. One group entered the Jurassic era an undisputed victor of the Triassic-Jurassic extinction, ready to dominate the planet…

K-Pg

The dinosaurs ruled the Earth for over a hundred million years. Evolving out of the archosaurs, the clade also comprised bird-like and crocodylian members, filling up every niche imaginable (other than producers, of course).

As it stood, their era could have continued for much, much longer than it actually did. But fortunately for us (and the 66 million years of ancestors that preceded us), one single space rock managed to end their run, at least for the most part. Most of us already know the story – one fine day, an asteroid 10-15 kilometres in diameter (almost as large as Singapore, assuming it were spherical) plunged into the Yucatan Peninsula in Mexico, leaving behind an impact crater about 150 kilometres wide.

The initial explosion, equivalent to the energy released by billions of nuclear bombs, was already enough to essentially sterilise the region surrounding the impact. It was the lingering after-effect of the impact that was truly deadly, though.

Over the following days, a massive tidal wave swept the globe, destroying coastal ecosystems and flooding inland areas. The heat and light from the initial blast would have had a regional impact, but the dust from the impact site was what contributed more in the months to follow, blocking the sun the same way the CAMP did back in the Triassic extinction, cutting off the food chain at its very base by choking out photosynthesis, and triggering a collapse of the ecosystem. Larger dinosaurs died, unable to adapt, and only those small and nimble enough to survive the environment with the limited resources available.

That’s the story we all know.

The story that you may not have heard is that of the dissenting opinion, of an equally dramatic catastrophe that came from deep within the Earth instead of from beyond the sky.

66 million years ago, a LIP known now as the Deccan Traps located in what would be present-day India underwent an eruption that lasted hundreds of thousands of years, spewing out massive amounts of greenhouse gases into the air. The events that follow would have been similar to those described earlier during the CAMP’s activity, and those who back this hypothesis suggest the Chixculub impact’s, well, impact, was only one of the two halves of the tale when it comes to the disappearance of the dinosaurs.

Nonetheless, this conclusion is highly disputed, with many researchers suggesting the dinosaurs would have been perfectly fine despite the Deccan traps eruption so long as they avoided the asteroid strike. Although some genera experienced an elevated rate of extinction due to volcanism and climate change before the strike, some studies show that the diversity of the dinosaurs had recovered soon after – and may even have been increasing when the asteroid put an end to it all.

Further debate is inevitable. One thing that is for certain is that there were beneficiaries of the extinction: mammals. Or rather, those little scurrying creatures that modern mammals originated from. Without the death of the dinosaurs, humanity as we know it would never have arisen, and mammals may just have been confined to the cold, dark crevices under rocks where our dinosaurian overlords wouldn’t notice us.

It’s not just mammals who benefited. Birds and crocodylian reptiles, two offshoots of the dinosaurs, proliferated so much that birds are now some of the most diverse taxa on land.

Regardless, it certainly seems like a terrifying prospect to be caught in one of these mass extinction events. Thank goodness we aren’t like the dinosaurs, staring down our own dooms …… What’s that?

We’ll see you again in the fourth and final instalment of the Mass Extinctions, where we will discuss what we can learn from the past and turn our eyes towards the present and future to think about how we can save the species of today.

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Image Credit: https://www.livescience.com/43295-triassic-period.html