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IAmTheFloydman t1_j4tzqs1 wrote

The impact hypothesis was controversial for many years, even after the Alvarezes published their findings in 1980 about iridium deposits that were almost impossible to explain any way other than an asteroid impact. Some scientists still favored existing hypotheses, including volcanism, sea level changes, and even chronic constipation. (See Keith M. Parsons' "The Great Dinosaur Controversy" published in 2003.)

Many scientists believed that major collisions between celestial bodies ceased long before the dinosaurs went extinct. It wasn't until 1994, when Shoemaker-Levy 9 crashed into Jupiter, that we witnessed such an event occuring. 100% undeniable proof that collisions still occured, which meant they definitely could have occured 65 million years ago.

There was also the problem of the impact crater. The original 1980 paper was based on iridium deposits around the world, but there was no known impact crater of sufficient size that could be dated to the right time. The Chixulub crater was discovered in the 1970s, but it wasn't identified as an impact crater until 1990. (Previously, it was thought it may have been a volcanic caldera.)

All this is to say, evidence has trickled in to support the impact hypothesis, and while the pieces were there in the 90s, it has taken some time to put them all together.

And the discussion isn't over either! While many experts got together and concluded in 2010 that an asteroid impact was the main cause of the K-Pg (formerly K-T) extinction event, there is still significant evidence that volcanism at least played some part. The dinosaurs may well have been on the decline for a long time, and the impact simply sealed their fate. Anyone who says "the asteroid killed the dinosaurs" is probably oversimplifying a complex issue, but it would be a huge mistake the ignore the asteroid impact altogether.

Source: A 2015 essay I wrote as an assignment covering a controversy in science during my undergraduate studies.

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icbmike_for_realz t1_j4u7pzk wrote

What does volcanism mean in this context?

Obviously it doesnt mean that a massive bunch of dinosaurs were too close to active volcano and melted.

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BobbyP27 t1_j4u9of0 wrote

Large explosive volcanic eruptions can pump enough particulate matter into the high atmosphere to interrupt weather patterns. One of the largest in recent history, the eruption of Mount Tambora in 1815, for example, caused the "year without summer", and a number of similar eruptions happened earlier in recorded history where we did not, at the time, know the source, but have since discovered the locations. We know from geological evidence, far far larger volcanic eruptions and events have taken place, and an event on such a scale could cause sufficient particulate matter to enter the atmosphere that it could create a period of several years of insufficient sunlight reaching the surface of the earth to massively disrupt ecosystems and create a mass extinction event. There is geological evidence that one such event, in the Deccan Traps of modern day India took place at the right sort of time (on a geological scale) and was large enough that it is a plausible candidate for causing the extinction event that ended the dinosaurs.

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CrustalTrudger t1_j4urjw2 wrote

> an event on such a scale could cause sufficient particulate matter to enter the atmosphere that it could create a period of several years of insufficient sunlight reaching the surface of the earth to massively disrupt ecosystems and create a mass extinction event.

So the potential cooling effects of large explosive volcanic eruptions (e.g., events like the 1815 Mount Tambora eruption) are not disputed, but this is not actually relevant for Deccan Traps volcanism or the suggested kill mechanisms related to them. For the Deccan Traps as the cause of the K-Pg extinction, the kill mechanism may have been global warming from pulses of greenhouse gases released by the volcanism (e.g., Tobin et al., 2012) or a combination of this along with ocean acidification and ocean warming (e.g., Keller et al., 2020). I.e., flood basalt eruption and its effects do not equal large caldera eruption and its effects.

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peoplerproblems t1_j4wlqp9 wrote

So you got me curious about multiple factors relating to the current and previous extinction events.

O-S was climate and atmospheric composition, greenhouse effect of volcanos, and loss of oxygen.

The Devonian event(s) were ecological, but I can't find much on it.

P-T was ocean acidification, oxygen loss, greenhouse caused by volcanism

T-J was again, acidification, climate changed, and oxygen loss.

K-G, again, acidification, climate change, but I can't find atmospheric composition.

Regardless, it appears that the extinctions occur once those worldwide changes start, regardless of the cause. What I'm curious about now is if there is any evidence at how inhospitable the planet was by the end of the extinction events.

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tandjmohr t1_j4wuw43 wrote

In this specific case they are referring to Flood Volcanism. The Deccan Traps (I probably spelled that wrong) are a large igneous province in India where, about the same time as the Dino asteroid (geologically speaking), large cracks opened in the crust and absolutely immense volumes of basaltic lava poured out in flows hundreds of feet thick covering thousands of square miles one on top of the other. The cumulative depth of these flows are measured in miles.

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icbmike_for_realz t1_j4wzltr wrote

Over what time span did these flows spread?
Would an individual dinosaur be overtaken or could they run away?

Or were they pressured by being pushed out of their environments?

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tandjmohr t1_j4x81hw wrote

Some of the individual flows happened within 50,000 years of each other. I believe the total time of the flows was 750,000 to a million years or so.

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