Deluge from above

[Jesrad]

I was looking at recent (=last decade) publications on geological history and mass extinction events, and I thought this was just awesome in a terrifying way, with appeal to space enthusiasts on top.

I've always had doubts about the "overhunting" hypothesis for how the pleistocene megafauna went extinct. That's mammoth, sabertooth tigers, megasloths, giant elks, mastodons and so on. On the surface it seems that at the time of the massive Younger Dryas climate weirdness (+10 to 20° C in average temperature, ocean level rising by 400 feet / 160 meters) humans went very mobile, migrated all over the place, and shortly thereafter those species went extinct. Naturally one would tie the two together, an explanation that is likely simple, clear and wrong (there's a lot of details that do not fit, like how the Clovis people in the south-east of north america could have extinguished mammoths on the west coast in a mere 300 years, all without leaving a single killing site, even though they never lived there). Correlation not being causation, maybe instead there was a common cause for both: we know from previous mass extinctions (Cretaceous-Paleocene, Jurassic-Trias) that when something REAL BAD happens, it is mainly the big animals that suffer while the most adaptable species can manage to thrive from the destruction. And I also know from anthropology (another hobby of mine) that primitive hunter-gatherer just do NOT extinguish species through hunting - because it's way too damn hard work and all of them always underuse natural resources around them, by a far margin. My point is, it is a lot more likely that the same thing that forced humans to migrate and invent new technology and use any edge they could, also did in the big game.

Oh and, just like with the K-T event, the YD is too geologically marked with a prominently visible, thin black layer of stuff with unusual isotopical properties.

At this point if you are thinking "Impact" you are correct and should give yourself a cookie

The hypothesis of a massive impact causing the YD extinction was first carefully formulated in 2007. It sparked heated debate because most geologists are naturally resistant to anything that might revive / reinforce beliefs about The Flood. There was botched replication, pointy words, flame wars and scathy counter-rebuttal. More publications followed on the trail, confirming the hypothesis of impact with a probable, massive (50 to 100 kms diameter !), carbonaceous chondrite 12800 years ago.

But, hey, there's more to it than just that. See, the climate weirdness of the time happened not in one big go, but rather in dozens of seperate but eerily-identical "smallish" events (which would still make our current Warming debate look like elderly people pointlessly bitching about the weather this morning), happening on an exact 1470 years period, AND one huge episode right in the middle. Those that happened before the YD big event are called the Dansgaard-Oeschger events, those after are the Bond events. They all have the same profile, same isotope deviation everytime, though they are a lot more localized.

OK fellow KSPers, this should lead you to the next step naturally.

Leaving this space blank on purpose to let you think it over.

Alright.

If you said "fragments with the same 1470 years orbital period" you win another cookie. It very much looks like some huge comet fragmented then hit the Earth over and over with each pass, with the bulk of it hitting 12800 years ago (and some other kind big part hitting just 8200 years ago too).

Now, how big a comet are we talking about here ? Surely not all the fragments have hit the Earth (or something else in the vicinity) ? Surely we can find traces of it still around ? Well, fortunately we CAN: it's called the Taurid complex, and comprises nasty stuff like geocruisers Adonis and Oljato, and even still has one active comet bit around (Encke comet). And, of course, a pair of anstronomers already suggested a possible link with the Younger Dryas back in 1982. Conservative estimates for the size of the progenitor comet is 100 to 200 kms, on par with Chiron. That's BIG. And, yup, the same astronomer Napier followed suit on the publications in 2010, reviving that aspect of the theory.

Now let's add something else to the mix: water.

See, a carbonaceous chondrite hunk of rock is usually about a quarter water ice. We also know that by the YD the levels of oceans rose a dramatic 400 feet / 160 meters. It probably wasn't all ice melting, but also exogenous water ice on top ! If the YD bolid was big enough (and it seems it was) it would have vaporized ice, from itself and from the miles of ice sheet it landed on (leaving no proper crater), in the Earth's atmosphere, maybe even in a suborbital arc. The spray could very well have flash-frozen mammoths standing, from thousands of miles away.

How cool is that ?

And here is a final nugget to chew on, although this one is stretching it thin: make the progenitor comet 2500 kms wide, and it would have held enough water to rise the oceans 2 whole miles. But that would necessitate much rewriting of what we think we know about Earth's past.

[-Velocity-]

There's not enough evidence of a large impact just 10000 years ago. There is no crater, no asteroidal dust layer. We have ice cores going back like 200,000 years, and any such impact would leave an obvious, unmistakable layer in them. Heck, we probably would have known about this impact before we discovered the Chixculub impact that killed off the non-avian dinos. All the other purported impact layers supposedly associated with a YD impact have been shown to be not from an asteroidal or cometary origin, or at the very least, have been shown to be unlikely to have been caused by an impact.

You honestly think that a 50 km+ wide asteroid could have hit Earth only 12000 years ago? That's laughable. Such an asteroid would pack at least hundreds of times more energy than the one that killed off the dinosaurs and likely leave an impact crater five hundred miles across, if not bigger. There would probably still be volcanic activity in the crater today, and almost all life on Earth would be destroyed by such an impact. Certainly humans could not have survived such a thing. It would probably be the biggest, or one of the biggest, impacts Earth had sustained since at least the Late Heavy Bombardment like 4 billion years ago. It would certainly be the largest known impact with Earth, other than the one that caused the formation of the Moon.

Anyway, you need to re-examine your position because it lacks scientific or logical basis.

Edited September 8, 2014 by |Velocity|

[ZetaX]

The 50km seems to be made up, at least I don't see that number in the link given. For significantly smaller ones, the first link gives some models on how they avoided creating significant craters.

[Idobox]

But, hey, there's more to it than just that. See, the climate weirdness of the time happened not in one big go, but rather in dozens of seperate but eerily-identical "smallish" events (which would still make our current Warming debate look like elderly people pointlessly bitching about the weather this morning), happening on an exact 1470 years period, AND one huge episode right in the middle. Those that happened before the YD big event are called the Dansgaard-Oeschger events, those after are the Bond events. They all have the same profile, same isotope deviation everytime, though they are a lot more localized.

From the wiki page you linked to:

The dating issue was largely solved by the accurate dating of the NGRIP core.[13] Using this dating the recurrence of Dansgaard–Oeschger events is random consistent with a noise induced Poisson process.[14]

Also I couldn't find anything on the isotopic irregularities, but tephra from a German volcano are effectively found all around the world at that time. But according to experts, the volcano was not nearly big enough to cause something of that scale, more something like a year or two of slightly lower temperatures.

It is generally admitted that the YD transition was caused by disruption of North Atlantic currents by large amounts of fresh water coming from North American Glaciers.

Anyway, climate change is porbably not the main cause of the holocene extinction, since there are extinction events at different times for different landmasses, corresponding with arrival of human.

For North America, a common hypothesis is that hunting caused a notable reduction in the number of mammoths and mastodons, which might by itself have caused large predators to go extinct, but that mostly caused prairie and tundra to turn into forest.

For many islands, we know overhunting recently lead to extinction of megafauna. In New Zealand, moa and Haast eagles disapeared within 2 centuries of human arrival. Madagascar was settled by humans 2000 years ago, and the 17 largest species of lemur disappeared since then, a large feline, 2 giant aardvarks and tiny hippos disappeared within 1000 years. In New Caledonia, land turtles and crocodiles went extinct within centuries of settlement, and all over the world, you will find that island megafauna disappears very quickly when human arrive, the smaller the island, the faster the extinction.

For Australia, an extinction event occurred 45 000 years ago. 43 000 ago, a land bridge with Tasmania is created, and within 2000 years a similar extinction event happens in Tasmania. And these dates fit with the oldest traces of human settlement, and the main hypothesis is overhunting.

[Brethern]

You honestly think that a 50 km+ wide asteroid could have hit Earth only 12000 years ago? That's laughable. Such an asteroid would pack at least hundreds of times more energy than the one that killed off the dinosaurs and likely leave an impact crater five hundred miles across, if not bigger. There would probably still be volcanic activity in the crater today, and almost all life on Earth would be destroyed by such an impact. Certainly humans could not have survived such a thing. It would probably be the biggest, or one of the biggest, impacts Earth had sustained since at least the Late Heavy Bombardment like 4 billion years ago. It would certainly be the largest known impact with Earth, other than the one that caused the formation of the Moon.

Anyway, you need to re-examine your position because it lacks scientific or logical basis.

We only have theories as to what a huge asteroid hitting earth would do. Until one hits we will never know for sure what happens.

Humans are allot tougher than you think they are, and we're intelligent enough to adapt to new circumstances, as to where one could hit that wouldn't leave an obvious crater, well what covers 70% of earth's surface? and is most likely going to be hit?

[TNM]

A 50km Asteroid could hit anywhere, it would just vaporise the water and hit the crust anyways...too much energy to absorb by a mear few km of water. We would have all kinds of geological evidence of tsunamis (worldwide at the same time), the ashes from the following fallout in the ice layers (everywhere on the planet) and so on.

Nope, only 12000 years ago? Not in any way, shape or form, not enough time to remove the geological evidence. And we can model quite well what would happen, because today we understand basic physics...mass/velocity/energy...its not rocket sience...well maybe it is

Edited September 8, 2014 by TNM

[Technical Ben]

There's not enough evidence of a large impact just 10000 years ago. There is no crater, no asteroidal dust layer. We have ice cores going back like 200,000 years, and any such impact would leave an obvious, unmistakable layer in them. Heck, we probably would have known about this impact before we discovered the Chixculub impact that killed off the non-avian dinos. All the other purported impact layers supposedly associated with a YD impact have been shown to be not from an asteroidal or cometary origin, or at the very least, have been shown to be unlikely to have been caused by an impact.

You honestly think that a 50 km+ wide asteroid could have hit Earth only 12000 years ago? That's laughable. Such an asteroid would pack at least hundreds of times more energy than the one that killed off the dinosaurs and likely leave an impact crater five hundred miles across, if not bigger. There would probably still be volcanic activity in the crater today, and almost all life on Earth would be destroyed by such an impact. Certainly humans could not have survived such a thing. It would probably be the biggest, or one of the biggest, impacts Earth had sustained since at least the Late Heavy Bombardment like 4 billion years ago. It would certainly be the largest known impact with Earth, other than the one that caused the formation of the Moon.

Anyway, you need to re-examine your position because it lacks scientific or logical basis.

People are very quick to forget. Even more able to brush over the facts. Was there a large impact just a few thousand years ago? Unlikely, but still possible. Is this the kind of evidence to support it? Not really, but it can be held with as much reasonableness as many other "theories". It's best to consider them as just that though.

As an example of how quickly things can change, we can forget, and we can brush over the evidence. Try to consider what the Amazon Rain forest looks like. Think for a moment on our current understandings, beliefs and concepts of it. Now consider what recent history thinks of it. Then past history. Then for a moment, how it all changed when the first western/European settlers "discovered" the continent. We currently forget it was covered very much like Europe was with the Roman Empire, but with it's own indigenous peoples. Now it's a Rainforest, but it was not always that way, even within "recent" history.

We forgot, we did not search, and only just recently did we rediscover the simple truth. The Rainforest use to be cities. How quickly can our world change, and how quickly can our worldview?

This in no way implies other understandings are wrong. It just means arguments such as "but obviously there would be X evidence" or "obviously it would take thousands of years" don't hold much weight. Extraordinary claims do need extraordinary evidence. But the best way to show that is to encourage others to learn more, and from there look at what evidence points to, and accept whatever reality it holds out.

If someone points out a bright light in the sky, it's less helpful to say "impossible", and more helpful to ask them what they mean... the sun? A star? Or perhaps it's your house on fire!

Idobox covers the explanations of the observations quite well.

Edited September 8, 2014 by Technical Ben

[TNM]

There is a fundamental difference of geological evidence a 50km-asteroid impact would cause and a forgotten city overgrown in a rainforest. Now, to understand why would need you to take some time to understand the basic principles of physics and geology, its actually very interesting once you get into it, and its very much space related too (forming of the solar system? exciting).

But don't argue with "i don't know so you can't know either". Once you have the basic principles down you may still not be able to draw every detail, but you can outline very well what absolutely must happen. Thats what sience does, once you understand the principle you can make predictions, the predictions get tested again and again and a model developed accordingly. Then, you can feed anything into the model and get solid predictions for events you can't directly test. Thats why its different from "believe".

[Brethern]

A 50km Asteroid could hit anywhere, it would just vaporise the water and hit the crust anyways...too much energy to absorb by a mear few km of water. We would have all kinds of geological evidence of tsunamis (worldwide at the same time), the ashes from the following fallout in the ice layers (everywhere on the planet) and so on.

Nope, only 12000 years ago? Not in any way, shape or form, not enough time to remove the geological evidence. And we can model quite well what would happen, because today we understand basic physics...mass/velocity/energy...its not rocket sience...well maybe it is

And what does water do when it finds a lower area than where it's at?

It flows into it.

could it be that a crater would be completely filled with water? and over the years the currents eroded and shifted silt into it?

Yes I am aware that physics indicates what a massive object hitting at such and such a speed should do damage wise, however you'd have to calculate it for the mass off all known materials and assume that the object was completely made from such materials.

Even then there's plenty of probabilities and unforeseen circumstances that will change those results.

[Kryten]

The tsunami deposits from chixclub were so huge they're readily identifiable today. 12k years won't do what 65g couldn't.

EDIT: this isn't even relevant, anyway. The younger dryas hypothesis involves an impact on north america, not just the earth.

Edited September 8, 2014 by Kryten

[MockKnizzle]

I'm not sure why everyone is talking about a 50km impactor, since that's not what the article the OP linked is talking about at all. For those who didn't read, the hypothesis is that 12800 years ago the Earth passed through the Taurid meteorite complex (which originated when a large comet fragmented into millions of pieces on its way through the inner solar system), resulting in the simultaneous impact of thousands of smaller meteorites across most of North America. Most of these fragments exploded in a massive storm of airbursts (like the Tunguska event, but larger) that heated the atmosphere to temperatures so enormous that a large portion of the surface was vaporized and blown away in giant supersonic flows of gaseous rock.

There is no evidence of a large crater anywhere because there wasn't a single large impactor, but a storm of many thousands of smaller ones all in a very short (seconds to minutes) timeframe.

I read the entire article, and I must say that the author's analysis of the geographic evidence for such an impact storm was pretty compelling.

[Technical Ben]

There is a fundamental difference of geological evidence a 50km-asteroid impact would cause and a forgotten city overgrown in a rainforest. Now, to understand why would need you to take some time to understand the basic principles of physics and geology, its actually very interesting once you get into it, and its very much space related too (forming of the solar system? exciting).

But don't argue with "i don't know so you can't know either". Once you have the basic principles down you may still not be able to draw every detail, but you can outline very well what absolutely must happen. Thats what sience does, once you understand the principle you can make predictions, the predictions get tested again and again and a model developed accordingly. Then, you can feed anything into the model and get solid predictions for events you can't directly test. Thats why its different from "believe".

Never disagreed with it. But the "it's impossible" is less helpful to people. "This is what is possible" is much more helpful. It's always best to build knowledge before knocking it down.

Sometimes evidence points to small things, and by brushing off the evidence, we rule observation to be wrong. Observation is never wrong, just our theories/ideas/conclusions on it.

[Jesrad]

There is no crater

Not all big impacts leave a nice Barringer-type crater, especially when they're of the airburst sort. However there ARE hundreds of craters all over central Mexico exactly where they should. Read the initial link for their photos and coordinates.

no asteroidal dust layer.

Yes there is, and it contains stuff that cannot exist on Earth without a big impact. You didn't bother to read it ?

Heck, we probably would have known about this impact before we discovered the Chixculub impact that killed off the non-avian dinos.

Some apparently speculated about this as early as 150 years ago. And some posit it was the basis for all the Flood myths in every human culture, so we might have known about this all along, in a way. Our direct ancestors having been around at the time and passing it down in oral culture, you know.

almost all life on Earth would be destroyed by such an impact. Certainly humans could not have survived such a thing.

Well a lot of life on Earth died, and the Clovis people disappeared. Volcanic activity flared up durably. Climate went bonkers.

We would have all kinds of geological evidence

Like the 350,000 cubic miles of fresh, uneroded ignimbrites near central Mexico ? Like the melting of the Laurentiide Ice Sheet ?

I'm not sure why everyone is talking about a 50km impactor, since that's not what the article the OP linked is talking about at all

Ah, someone who actually reads the links, thanks. The first link is the best synthesis on this whole problem that I could find. It's balanced and factual and not overly conclusive. So far from all I've read on the subject the impact hypothesis is the one that makes a lot more sense than every other alternative. I included the wilder ideas around it because they're badass, I don't believe them myself (I am forbidden to believe by my religion).

The 50-100 km radius mentioned is for the total lump of mass from which the Taurid complex is thought to have originated, the other 50 km diameter mention is for the sum of mass that is supposed to have mostly airburst in lots of fragments all over north america 12800 years ago, in 2 major clusters of hundreds of 2km-sized chunks. And Tunguska might very well have been another 100m fragment of the same, too. Some suggest a link between those and the 9P/Tempel comet too - not sure why.

Edited September 10, 2014 by Jesrad
typos

[YNM]

I haven't read the links, but just some comments : have you looked for other comets (or bodies) with similar Tisserand value ?

1470 years is the same as a semi-major axis of 129.28403 AU. I do understand that finding objects with similar semi-major axis is hard, hence why I asked a Tisserand value. The only thing we lack now is the other 4 orbital elements...

[Jesrad]

I have no idea, I'm no astronomer I just loosely rely on Napier's papers here (links in the first post) maybe you can look in there ?

[YNM]

The paper used orbital parameters of comet 2P/Encke straight out. Most of the debris distribution mentioned in the papers are models... But my main attention is that comet Encke have a fairly short period. This means that the 1470 yr period must be some sort of culmination, if it is directly related to the comet 2P/Encke.

If it's not, maybe one needs to use the tisserand value, changing the orbital parameters of Encke to the unknown object.