The Asteroid That Killed the Dinosaurs Created the Amazon Rain Forest | Hacker News Reader

The Asteroid That Killed the Dinosaurs Created the Amazon Rain Forest

scientificamerican.com

106 pointshheikinh79 comments

Out of curiosity, when did the asteroid extinction theory cement as the scientific consensus?

I seem to recall that in my childhood (1980s, Canadian elementary schools) it was still treated as only one of several competing explanations, but now it’s pretty much an accepted fact.

Which makes sense given all the evidence, but I still have this odd sensation making me feel like I missed the memo! Am I the only one who feels this way?

Answering my own question: https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e...

So I guess it was indeed proposed around the time I was born and “proven” by the time I had outgrown dinosaurs as an interest/hobby...

> With the exception of some ectothermic species such as the sea turtles and crocodilians, no tetrapods weighing more than 25 kilograms (55 pounds) survived.[5]

I wish we could unite and start forming a plan to survive the next one. I wonder what that would entail?

Detect it early enough and we can nudge it out of our way with a large rocket. Problems include: solar system is big, comets have really long orbital periods, we need to be good enough at predicting the path to be sure that the nudge is putting it in a good orbit we like and not setting us up for disaster. We do look for asteroids with the impression that if they ever found one coming out way we'd do a mission to stop it (though I don't think that's a real commitment.)

See: https://en.m.wikipedia.org/wiki/Asteroid_impact_avoidance

The dinosaurs really messed up by not having a space program.

If they really wanted to survive, they should have prioritized colonization of Mars over their silly interspecies zero sum resources-based conflicts.

If you can survive mars you can survive asteroid scoured earth.

Well, there a is a theory that dinosaurs evolved into a transwarp capable species, now residing over in the delta quadrant...

[0] https://memory-alpha.fandom.com/wiki/Voth

Oumuamua wasn’t detected until after it passed by the Earth so it’s a hard challenge to detect from far away.

I believe it came a close as 0.16 AU (tracing the path backward), which is 66 times further than the moon.

Being an interstellar object though, it moves faster than the escape velocity to the sun, so it would pack a higher energy per unit of mass than a regular comet or asteroid. Fortunately such objects are also somewhat rare.

OK, crazy idea time.

Couldn't we detect such things with radar? Given the right frequencies, rocks and dirt will reflect - that's how terrain-following radar works.

So yes, I think we could, but there are some significant problems.

1. 1/r^2 power loss, in both directions. We would need a massive radiator, and very sensitive detectors.

2. The detectors are in the wrong place. You send out your signal, and several hours later the response comes back, by which time the earth has rotated. So where your detector has to be depends on the distance to the object, but you don't know the distance to the object!

So we'd need a bunch of detectors at various points around the globe. And we'd need a huge power source.

Which brings me to solar flares. They emit radio waves. Do they emit enough power at the right frequencies to be useful for this?

Detect it early enough and we could just paint it, apparently just a significant change in albedo will change the orbit over time.

I don't think we have a proven paint-in-space technology but we definitely have proven 'hit with rocket' technology.

Yeah, but hit it with rocket won't change the orbit of any object that might cause the civilization serious problems.

Even nukes have a surprisingly small effect, unless they are buried. We have landed on on an asteroid, but have yet to embed a nuke in one.

The trick about nukes is you have the risk of just making an harder to stop by making a cloud, like say comet levy which turned into 21 pieces, but delivered the same total energy when hitting the atmosphere.

The nice thing about the paint is that it's not that hard, even asteroids have gravity, and we have orbited (very slowly) asteroids before. It doesn't cause the astroid (which might just be a loose collection of rocks) to break up, and you get a huge win per pound of delivered mass, granted it takes months or years to accumulate into a large orbital change.

I would think a broken-up asteroid would be better, in that the worst possible outcome would be exactly the same as not hitting it, with all the pieces undisturbed enough to still hit the earth.

However there would be more surface area to burn up in the atmosphere, and if you do it far enough out and I'd think it would require very little nudging to move pieces out of the way

Sure, if 50% of the mass of the resulting explosion burns up in the atmosphere it's a huge win, but maybe not enough. But if it was as big (or bigger) than the dinosaur killing object (there's some debate if it was a comet or asteroid), it might just split into a few pieces that will come through the atmosphere intact.

Generally if it's a planet killer you want to take no chances. The earlier the detection the better, and changing the albedo will work if it's a sand up to a solid rock.

I've heard similar proposals with a "gravity tug", but it's not clear to me that it would work with a significantly larger change in velocity than just using the fuel directly. Keep in mind that the asteroid that killed the dinosaurs was approximately 10km (some sources) to 15km (other sources) across, and we have no reason to think that future asteroids might not be bigger.

The largest atomic crater I could find was from a 104 kiloton bomb that created a 400m wide and 100M deep. Both the USA and Russia has similar tests, and that would be just a small dent in a 15km across asteroid. Both were from 100-200m deep explosion, and it's not clear if deeper would necessarily be better. Sure you might crack a 15km long asteroid into two pieces, but it wouldn't help much. Vaporizing a 15km asteroid is going to take WAY more than 100 kiloton.

What might work is some kind of nuclear engine that melts stone/sand/ice and ejects it at high velocity, working it's way into the center of the asteroid. It would need a throttle to only fire when it helps and idles when it doesn't.

What about 50MT? Tsar bomba hit that. Geopolitics aside, is larger possible?

If your asteroid or comet manages to get broken up into many smaller fragments, but all or most of them still reach the earth, but are small enough to burn up in the atmosphere before impact, their total energy would still be transmitted via atmospheric entry friction heat, which itself could cause lethal global air temperature increases. They might last only a few minutes or slightly more but (the science on this is a bit ambiguous) we could still be talking about temperatures going up into the hundreds of degrees. No big bang, but still catastrophic for crops, plants, forests, people and atmospheric health.

more telescopes and more rockets!

Well, these guys are working on getting humanity through smaller but similar events through feeding people despite years without any crop growth.

https://allfed.info/

We've actually got a fairly decent handle on asteroid protection right now with the cataloging work that's been done in the last couple of decades. Comet impacts, supervolcanos, and possibly a nuclear winter are really the biggest threats of this sort

NASA told Congress in 2007 that we can nuke asteroids before they get too close. [0]

In the impulsive category, the use of a nuclear device was found to be the most effective means to deflect a PHO [Potentially Hazardous Object]. Because of the large amount of energy delivered, nuclear devices would require the least amount of detailed information about the threatening object, reducing the need for detailed characterization. While detonation of a nuclear device on or below the surface of a threatening object was found to be 10-100 times more efficient than detonating a nuclear device above the surface, the standoff detonation would be less likely to fragment the target. A nuclear standoff mission could be designed knowing only the orbit and approximate mass of the threat, and missions could be carried out incrementally to reach the required amount of deflection.

[0]https://www.nasa.gov/pdf/171331main_NEO_report_march07.pdf

In simple terms a good space program. More sensors, more tracking objects, and the ability to get mass anywhere in the solar system to give an object a small nudge well ahead of impact.

Neil deGrasse Tyson has made many similar comments, one quote “Dinosaurs are extinct today because they lacked opposable thumbs and the brainpower to build a space program.”

There won’t be a next one. Not for us at least. We’re destroying our habitat to the point that we won’t be able to survive. Something better suited to the environment we’re creating will take our place.

This part in particular:

https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_e...

I think was around when consensus shifted from "Yeah this is probably what happened" to "This is it"

I'm curious if the Deccan Traps, (https://en.wikipedia.org/wiki/Deccan_Traps) formed at about the same time on the opposite side of the planet were also caused by the asteroid. Not a standard theory but it makes sense to me that an asteroid hitting one side of the globe could cause shockwaves that crack the crust on the other.

Check out this 2-year-old New Yorker article, https://www.newyorker.com/magazine/2019/04/08/the-day-the-di...

The Chicxulub crater off the top of the Yucatan peninsula is attributed for that particular event. It wasn't really known until the early/mid 90s I don't think.

Right. Although even after the discoveries related to the K-t boundary and the crater, there was a school of thought that it was just a contributing factor to a pre-existing general decline. My understanding is that there's now a general consensus that it was much more of a singular cataclysmic event.

There's still a substantial group that thinks the impact was part of a 1-2 punch with the eruptions of the deccan traps, which produced a far larger impact on the atmosphere but over a longer period of time. Iridium from the asteroid impact is found in the basalt deposited by the deccan traps, so they definitely happened concurrently.

That said, if you look at the patterns of extinction, survivors seem limited to things that could hide in burrows or in deep water and then survive for an extended period exclusively on scavenging, as if everything that happened to be on the surface was suddenly killed and then photosynthesis stopped working for a few years. Notably, species that would normally be very sensitive to climate change like small amphibians survive whereas generalists capable of long distance migration die out. There may have been ecological stress beforehand but a singular cataclysmic event turned it into a mass extinction.

so they definitely happened concurrently

Do we know for sure that the volcanism in the Deccan traps wasn't caused/triggered by the asteroid impact? I know they're pretty much located at the opposite ends of the world, so could the shockwaves from the initial impact have created an amplified node at the other side?

(edit: wikipedia[0] says it's inconclusive:

> Although the Deccan Traps began erupting well before the impact, [..] the impact may have caused an increase in permeability that allowed magma to reach the surface and produced the most voluminous flows, accounting for around 70% of the volume

[0] https://en.wikipedia.org/wiki/Deccan_traps#Chicxulub_crater )

While there are many large igneous provinces similar to the deccan traps (for example the siberian traps associated with the Great Dying), we don't really have any good evidence for large asteroid impacts comparable to chicxulub so it's tough to say with confidence what effects were directly the result of it versus coincidental.

Well... I did some digging.

The Great Dying you speak of happened to coincide with an asteroid crater off the coast of Antarctica [0]. I haven't been able to find an accurate globe of the continents at that time ([1] doesn't show the poles in great detail), but it does look like eastern Siberia was at the antipode of the Australia/Antarctica boundary. So the theory seems to hold up -- at least from the confines of my armchair, that is.

[0] https://www.universetoday.com/8221/huge-asteroid-crater-in-a...

[1] https://resize.hswstatic.com/w_907/gif/cretaceous-map.jpg

The crater was well known to oil and gas people long before that, but the knowledge didn't make its way to academic geology until the 90s.

IIRC, oil and gas companies knew of the crater, but that knowledge was for many years proprietary information belonging to Mexico's state-owned oil company Pemex who paid significant money for the geological studies of the area.

I don't know. A couple of years ago I read a piece in (I believe) The Atlantic that proposed it was a massive volcanic eruption that did the dinos in. The sub-plot of the article was how science gets attached to an idea (i.e., it was an asteroid) and more or less self-fulfills that idea despite plenty of evidence that calls it into question.

Found it!

https://www.theatlantic.com/magazine/archive/2018/09/dinosau...

The idea that we can know with any degree of certainty that an event tens of millions of years ago was the single cause of dinosaur extinction is absurd. It’s bad science.

Case in point, a pandemic could have wiped out all the dinosaurs 1 million years before the asteroid hit and we would have no fossil evidence of that.

The asteroid theory is still just a theory and for anyone to be arrogant enough to say that it is fact doesn’t deserve to teach science in any capacity.

Adding in additional events that we have no evidence for would also be bad science.

https://en.wikipedia.org/wiki/Extinction_event#Other_hypothe...

I’m not saying that they were killed by a pandemic. It’s an example of something that could happen that would never be detected by fossil evidence.

There are potentially dozens of conceivable events that could have caused extinction level events and taking a single theory and selling it as fact is wrong.

We should be teaching it as a theory with pretty decent evidence but not much more than that because it’s impossible to say what really happened. Anything more than “this is a plausible idea with some pretty good evidence behind it” is science fiction, not science.

This seems to be a much more reasonable stance, though just because you can conceive of something doesn't mean it should be taken seriously.

Your previous comment included questionable phrases such as "any degree of certainty", "absurd", "just a theory".

My point is that we are talking about an event that happened 70 million years ago. Think about how long ago that was. The amount of evidence that is leftover after 70 million years of time passing is infinitesimally minute.

To think we can come to any conclusion with the tiny amounts of evidence that remains or to clue together all the remaining bits and pieces of residual evidence is extremely arrogant.

It makes for a decent story and hypothesis, and it sounds plausible. But to teach people that this is basically fact is absurd, which is my point. It should be taught as a theory.

You cannot dismiss entire branches of geology like that. The evidence is not "tiny" or "infinitesimal". Sure, it takes care, effort, and specialised techniques to find it, but it is there, and we need a theory that explains it.

Much of the research into geology has been funded by the oil industry, who are enormously interested in knowing these kinds of processes, in the hopes it will help them locate it.

Geology != figuring out how dinosaurs became extinct.

The evidences that remains after 70 million years is orders of magnitude less than the evidence that has been destroyed over the last 70 million years.

To take the morsels of evidence we have and think that paints a definitive answer is the height of human arrogance.

Referring to scientific theory as science fiction is a bit strong. The extinction of the dinosaurs isn’t Star Wars. Can we ever know exactly what caused that extinction event? No. Did a massive meteor hit the earth that likely could have done it? Yes. Could some other coincident event also contributed? Sure. There is, however, pretty strong modeling-based evidence that the meteor strike alone could have caused the mass extinction.

There's a big difference between "with perfect certainty" and "with any degree of certainty". We can't be pefectly sure that the scenario you outline didn't happen but the timing and the idea of a virus acting like that are so improbable that we can be almost entirely certain it didn't play out like that. We're not perfectly certain it was the impact, but we are very certain with all the evidence that has built up.

OK, but most of what we consider fact about any era (including the present) is a consensus understanding/belief based on the best available evidence -- if we're lucky.

Everything we are told or taught is a simplification, or a model.

The distinction between "fact" and "theory" is not always as clear as you imply.

An empirical epistemology (ie, science) would suggest that events we did not observe are proven by finding undeniable evidence that they occurred. "Consensus" and "best available" are not part of it. We cannot say for sure that a theory is fact simply because we form a consensus around a hypothesis supported by the best available evidence. That evidence may be insufficient to incontrovertibly support the hypothesis and consensus has often been wrong in the history of science. I would go so far to say that there has always been a consensus view that later turned out to be totally wrong.

The ability to doubt a proposition while simultaneously believing that it may indeed be true is a core psychological skill for any scientist. We ought not treat every theory that we believe to be true as "fact."

Consensus by humans doesn’t mean that it’s fact. By presenting the asteroid theory as fact is doing a disservice to science. It should be taught as a theory with pretty good evidence. I personally think this is the most plausible explanation but it’s when people call it fact or near-fact it makes me bristle.

It creates massive groupthink and stifles discussion on the topic which is worse, because it becomes politicized especially in this day and age.

I understand your point, and I agree. But there's nuance here.

Some theories, ranked by the strength of their supporting evidence, e.g. and IMO:

  0 Baby-eating lizard aliens run the US government
  1 ..
  2 String theory
  3 ..
  4 ..
  5 ..
  6 ..
  7 Asteroid extinction event
  8 Relativity
  9 Evolution

Scientists and specialists should draw a critical line between theory and fact. But there are always unknowables, and if "fact" requires the elimination of uncertainty ("10" in the above), then it is a useless word.

So we'd need a new word, that means "very well-supported theory, based on all available evidence, with no strong competing explanations". Open to suggestions here!

But for non-specialists, at what score is it reasonable to treat a theory as "fact"? I'll vote for 7.5. :)

Obligatory: Colloquially, "fact" as "true idea" -- not "quantum of isolated information which can be knowable". The latter definition is lovely, but has little application in the world of people.

Relativity is lower than evolution? I would put relativity at 9.5 because it can be verified with actual experiments today.

Regardless I’ll say the same thing I tell my kid which is the same as what you said. Everything that isn’t a fact is a theory with various levels of evidence. The stronger the evidence, the more likely the theory is correct. But a theory will weak evidence could suddenly improve if a new piece of strong evidence comes to light. And a strong theory could become weak if a piece of evidence disproves the entire thing. So keep an open mind and don’t mistake theories for facts.

> I would put relativity at 9.5

Fair point. It was crowded up there, and my physics is less than current.

I think we agree, really. I'm just not as strict on the semantics of the word "fact".

I agree that laziness on the margins of fact is lazy, esp for specialists. I don't think we can authoritatively say that anything is an absolute truth. But there are some really useful models.

The extinction event model serves a purpose for paleontologists, and it's pretty good for most of them. It serves a different purpose for non-specialists.

Well, clearly you don't subscribe to the same epistemology as the critical rationalists, etc. So naturally you bristle.

There are few facts, only conjectures that your sensorium fails to reject to various degrees. We then overload 'fact' to mean more things than logical truisms constructed from axioms and to extend to conjectures that we have collectively failed to reject despite strong attempts.

The asteroid extinction hypothesis is fact in this (mainstream) terminology.

Paleontologists have a much more detailed view of the past than you think. There are fossils of fish and trees killed by the asteroid impact itself, buried by the tsunami.[1]

> In the deposit, the team discovered an ancient freshwater pond whose occupants had been quickly cemented together by waves of sediment and debris. The fossils include sturgeon and six-foot-long paddlefish, their scales intact but their bodies ripped and smashed; marine mollusks; leaves and tree fronds, and the burned trunks of trees. The fish carcasses were not bloated, decayed, or scavenged, suggesting that they were buried quickly — and that few animals were left alive after the cataclysm to come digging.

> The fossil deposit also teems with tektites, tiny glass beads that are the telltale fallout of planetary-scale impacts. Fifty percent of the fossilized fish were found with tektites in their gills, as if the fish had inhaled the material. Also recovered were tektites trapped in amber. Their chemical composition was unchanged in 66 million years, and it closely matched the unique chemical signature of other tektites associated with the Chicxulub event.

[1] https://www.nytimes.com/2019/03/29/science/dinosaurs-extinct...

> It took six million years for the forests to return to the level of diversity they had before the meteorite, and the species that slowly grew back were completely different than what came before.

It's just very difficult to think in terms of these timescales, when all of human history is only a few thousand years.

Just imagine you've only got to trace your lineage through a few hundred ancestors to reach the beginning of recorded history!

Setting aside ancient history like Egypt, any sense of modern recording started something like 400 BC. At 20 years between generations, that's only ~120 generations.

With this accounting, the United States was founded ~12 generations ago.

And that was my initial estimate as well until I doubted my own knowledge of how long history has been recorded. Apparently the definition for some stretches all the way back to 4000 BC! So to account for this wide range of opinions I anticipated I would encounter on HN, I chose to be vague.

I'd argue that Human history starts at lest 3.3 millions years ago, when first stone tools were found.

“History” is often used to mean “written history” as in the opposite of “pre-history”. That seems to be the sense in which the parent is using the term.

In general "human history" starts with the first written word, around 10,000 BC. Everything before that is considered prehistory. Of course, humans didn't simply come into existence 12,000 years ago, but we have very little conception of life before The Word (tm).

Unless I'm unaware of some new discoveries, i believe the first written word (that is clearly identifiable as a written word) would be in cuneiform, around 3500 BC, in ancient Sumer.

You are correct. I was confusing human history with recorded history. Wikipedia tells me that human history starts with the agricultural revolution, around 10,000 BC. Recorded history starts, as you say, in the 4th millennium BC.

I'm pretty sure they were vandalizing caves long before they were writing cuneiform. Though it's debatable whether those illustrations counts that as "history" since it's more like a powerpoint than a memo.

I can't take another of Grug's hour-long rant about live stocks being down and how we need to divest from transportation.

I recommend nursing half a glass of wine to get just a wee bit lightheaded, putting on some ethereal music like Dead Can Dance, and reading on Wikipedia through the history of continent movements and formation and breakup of supercontinents. After a while such reading evokes rather curious feelings, and six million years won't seem so long when continents are swimming this and that way.

(‘A Passage In Time’ is a great compilation from DCD. E.g.: https://youtu.be/ajfVT_uk6j4)

Prior to 2013, it was commonly cited as having happened about 65 million years ago, but Renne and colleagues (2013) gave an updated value of 66 million years.

  -- https://en.wikipedia.org/wiki/Alvarez_hypothesis

My first thought reading this is, here they are casually adjusting the date by 1,000,000 years, and meanwhile homo sapiens is 200,000-300,000 years old. Helps illustrates the timescales a little.

Also cool: https://www.nasa.gov/content/goddard/nasa-satellite-reveals-...

This is really cool but I find it very hard to believe that this has the effect they are supposing here. We're talking about an area that's ~50% of Europe, so I believe microclimates can help much more than the dust from the other side of the world. It would be like saying the Europe only exists the way it is because of the gulfstream, be it in Ireland or Romania.

Also keep in mind that rhe Amazon rainforest is much more dense on the area around the Equator line, which happens on all over the world at this latitude, so there's nothing unique about Amazon here.

Another intriguing thing about this is that if this dust is so fertile then it's hard to believe that it would not impact in a positive way the african coast line around the Sahara.

It's terrifying to me that we still don't have a solution to prevent an asteroid of that size from wiping us out. I suppose they only come around every few million years, but still.

It's not terrifying at all once you grasp how astronomically challenging it is to pulverize or divert an asteroid of such scale:

https://www.vox.com/science-and-health/2019/3/7/18251559/ast...

It's still terrifying.

Its just more understandable that we haven't solved the problem.

When you consider that extinction events are cyclical and correlate with our solar system's oscillation through the galactic middle plane, you can bet life on this planet will get wiped out again and there's little we can do about it. The question is: how much time do we have left? (My guess is 20-30M years.)

Citation?

I don't think the primary source is online, but it was referenced in the article "Defining Intelligence-Favoring Galactic Parameters for targeted SETI searches" in the 15 Feb 2021 issue of the "Journal of the British Interplanetary Society".

Here is another one which relates it to the passing of our solar system throught the galactic plane: "Sun's Movement Through Milky Way Regularly Sends Comets Hurtling, Coinciding With Mass Life Extinctions", 2008

https://www.sciencedaily.com/releases/2008/05/080502092145.h...

``The Cardiff team found that we pass through the galactic plane every 35 to 40 million years, increasing the chances of a comet collision tenfold. Evidence from craters on Earth also suggests we suffer more collisions approximately 36 million years. Professor William Napier, of the Cardiff Centre for Astrobiology, said: "It's a beautiful match between what we see on the ground and what is expected from the galactic record."

The periods of comet bombardment also coincide with mass extinctions, such as that of the dinosaurs 65 million years ago. Our present position in the galaxy suggests we are now very close to another such period.´´

----

Edit: There are also papers which relates it to passing through spiral arms (different cycle).

Thanks. Your article echos the claims in the JBIS article of gravitational perturbations affecting the orbital dynamics of comets, etc. There's also the interesting (though highly speculative) dynamic of dark matter particle accretion in the Earth's core leading to temperature rise on Earth. The area outside the galactic middle plane is apparently DM-dense.

Creative destruction at its finest.

Could someone post a link to a PDF of the original article please?

Why not you?

Because I couldn't get scihub to work; I think my ISP may be blocking it, or else my browser has over active security settings.

How is your question contributing to the discussion? Mine had the potential to give participants access to the primary source under discussion :)

Reply on news.ycombinator.com