Size has even more to say for the energy though, since mass goes as r³.  Doubling the diameter multiplies the energy by a factor of 8, while doubling the velocity multiplies it by a factor of 4, and doubling the density only doubles the energy.  The possible range of asteroid impact sizes is also much bigger than the possible range of impact velocities or densities.  So I agree it's not completely rigorous, but it does make sense to associate size and energy.  

To be more rigorous, we can propagate the uncertainty in the contribution of density, velocity, and size through the calculation, which will result in contribution to the error bars.  Since E(ρ,v,r) = 2/3πρv²r³, the fractional uncertainty in E due to each of those factors follows

δE/E = δρ/ρ + 2(δv/v) + 3(δr/r)

So the uncertainty in radius (or diameter) matters as much as the uncertainty in density and velocity combined.  

Some asteroids are binaries, and there are even a few claimed binary impact structures on the Earth (though some commonly-believed binary craters have later been proven unrelated to each other, like the Clearwater Lakes).  Probably the most compelling case of a binary impact, at least that I am aware of, is the Lockne crater and its neighbor Målingen in Sweden.  Their ages are well determined and consistent with one another, and the parent asteroid was also tied to a known main-belt asteroid breakup event 470 million years ago.  


Good review of the K-T extinction, Stellarator.  I also have not seen any convincing evidence of multiple impacts being responsible for it.  As you say, the Boltysh crater is fairly small (perhaps ~10⁵ Megatons of energy vs ~10⁸ Megatons for Chicxulub), and from the size-frequency relation of terrestrial impacts,

[center][/center]

[left]we expect an impact of that energy to happen on average once every few million years.  So it is both statistically likely to see such an impact that close in time with Chicxulub but be completely unrelated to it, and we don't get K-T level mass extinctions from this magnitude event anyway.[/left]

Wat thanks for the chart and info.  You mentioned binary asteroids and that reminded me of something- didn't something like that occur relatively more recently when an object impacted the Chesapeake Bay region (and created that body of water) while a second one hit just east of Toms River, NJ and may have caused a megatsunami there in PreColumbian times?  There is some evidence of either an extremely high level hurricane (Cat4 or higher) or an impactor that displaced the sediment in the region prior to about 1400.  It's also been conjectured that an earthquake hitting the Canary Islands would cause a cataclysmic megatsunami hitting the region.

Another fascinating thing about the K-T event is the chance that it might not have been just one impact, but a series of impacts that occurred near the same time, perhaps a larger asteroid that broke apart into two or more pieces or maybe a small "family" of asteroids that travel together.

I find this to be unlikely, though still plausible. There has been a lot of debate over this, obviously, but the general consensus is that the K-T "mover and shaker" was a fairly solitary and random asteroid. Yes asteroid impacts are considered cyclic due to there solar-system origins - but this is only roughly so. There is also some research suggesting that mass extinctions are on a cycle of some type, but it would take a bit more investigating to see if asteroids or asteroid showers operate on a similar schedule.  A key bit of information here are the exact details and position of the K-T asteroid impact. It is tricky to say, because the pieces of a broken-up asteroid would fall roughly in the same area, resulting in a sole crater. Still, one would still expect other craters present, but so far few have made the cut. The closest we've come to occurring near the time of the Chicxulub impact the Boltysh crater in eastern Ukraine. It's age was an uncertain 105 million to 88 million years old, but recent argon-argon dating has placed from being made within 600'000 years of the K-T.  It's impact wouldn't have been enough to trigger an extinction though.

The other detail to consider is WHERE the main K-T asteroid hit. It struck shallow water, unfortunately right on top of sulfurous sedimentary deposits. The resulting dust, sulfur aerosols and vaporized water had plenty of effect on the extinction, but also severe earthquakes and tsunamis were present. I say this as a rather unnecessary recap because the thought here is, that if the K-T impactor had not hit the sediments and shallow water, and instead hit the deeper waters of the Atlantic, or bare rock, it's impact effects would have been much less severe, resulting in no or a very reduced extinction. Hence, we can make a tentative conclusion that the Chicxulub was the sole impact of the time.

I wonder if the extinction would have happened anyway because the earth was changing at that time.  Wasn't the amount of oxygen in the atmosphere back then much higher thus the animals were much larger and the vegetation far more lush and tropical all over?  The mass extinction would have probably happened anyway though maybe not quite so abrupt.  Besides dinosaurs lots of other creatures died too, I think 75% of all, including sea creatures.  It was the second largest mass extinction we've had (the largest one being the Permian one which killed off 90% of all life and which may also have been caused by an impactor or even a possible gamma ray burst?) And of course we are in the middle of the sixth mass extinction in the history of the planet right now (with it being predicted that half of the species alive today will be extinct by the end of the century) and that is entirely caused by humanity.....
About (natural) mass extinctions there actually may be some benefit to them, since punctual evolution (mass extinctions every 60 million years or so) holds that mass extinction lead to periods of accelerated evolution and enhanced biodiversity.   Sort of like forest fires.  Of course the human-induced versions are only destructive and not useful because of how much more rapidly they occur.   It's the antidote to overpopulation (which will perhaps also be humanity's fate one day if we never colonize other worlds and get interstellar travel.)  I do believe in the Gaia theory which holds that the planet self-regulates to favor biodiversity over dominance of any one species and extinction eventually results when one species becomes too dominant (including us) when it reaches a tipping point and uses up too much of its resources.  When we damage the environment we damage ourselves because we are a part of that environment.  Thats because Earth is a (relatively) closed system and we need to colonize space in order to get beyond its limits (while still practicing sustainability.)

(the largest one being the Permian one which may also have been caused by an impactor or even a possible gamma ray burst?)

Probably no.  There has been a lot of study on the end-Permian extinction in recent years, with better geochronology constraints and fossil evidence, which have greatly narrowed down the list of possible causes.  The leading theory now is that it was caused by extreme temperature rise and ocean acidification that followed a period of volcanic activity, with the later consequences being particularly devastating to marine organisms.  The combination of these best fits the timing and pattern of extinction, and I talk about it in more detail in an earlier post here.

I wonder if the extinction would have happened anyway because the earth was changing at that time. 

An interesting idea, but again probably no.  It's hard to say what would have happened if such a catastrophic event did not occur, but still, timescale of change matters a lot for determining the pattern of an extinction (which species survive, thrive, or die out), and it's hard to imagine how the pattern of the K-T extinction would have happened anyway without a large impact.  Also, the dinosaurs did not die out.  They are still with us today as birds. :)

Yes they are!  Something really interesting I read awhile back was that the differences between dinosaurs and birds are so few and that in their embryonic stage they are basically the same until one gene for growth gets turned off and birds dont grow any further.  If we could keep that gene from turning off then birds would be as big as their ancestors were!

I wonder what caused that gene to turn off?  Just a mutation that evolution selected for?  Also weren't the big dinosaurs slowly dying out anyway?  And did the impact bring about flowering plants or was that due to changes in climate that were already happening?  Interesting that there were no ice ages back then and all land was concentrated on one supercontinent.


Thanks for the link to the other post.  I found that fascinating!  It also made me wonder about supervolcanoes like Yellowstone and its connection on the other end in Indonesia, when they finally blow, how bad it could be.

I also got distracted (in a good way) by your dark matter cosmological simulation and it seems like that may give us a reason for why galaxies cluster in large groups with supervoids in between.

Oops, size was diameter, not mass.  Ballpark energy.  Fair enough.

Causality is something that breaks down at fundamental levels....here is another one, what about retrocausality?

If we could keep that gene from turning off then birds would be as big as their ancestors were!

Indeed. There is a rather cool project organized by the world-famous paleontologist Jack Horner that is trying to cultivate the suppressed dinosaur genetics in chicken-stock to breed a small dromaesaurian. I could explain the whole process in the exhaustive detail only a dinosaur enthusiast and bachelors in science can muster, but Horner himself presents it rather well here in a TED talk:


[youtube]0QVXdEOiCw8[/youtube]

Also weren't the big dinosaurs slowly dying out anyway?

There is little evidence for this. Dinosaur speciation was at it's height during the later stages of the Cretaceous, as any peek into a dinosaur encyclopedia or trip to museum will confirm. Some have argued that this is just a geological bias, because Cretaceous rock fossilizes better then those rock of other strata, but this is not generally accepted. Dinosaurs were diversifying at an explosive rate during the late Cretaceous - if anything, the global cooling and subsequent dramatization of seasons during the Campanian and Maastrichtian Cretaceous stage made them adapt even faster.
The only true declination in diversity in the animals at the time were among the pterosaurs - a clade or order of creatures that are actually not dinosaurs, despite what many people believe. They belong to the distinct order of pterosaumorpha, whereas dinosaurs belonged to the clade Dinosauria. The reason for the pterosaur's decline and loss of the dominion of the skies was due to... more dinosaurs. Birds, in fact. By the end of the Maastrichtian stage of the Late Cretaceous, there was only around 6 species of pterosaurs left in the world - all belonging to the family Azhdarchidae, the most well known species being the gigantic Quetzalcoatlus northropi: Compare that to pterosaur populations from earlier times in the world, with thousands of known species from dozens of families. As Watsisname mentioned, birds ARE dinosaurs. So in light of this, one could say that the dinosaurs had solidified their claim to global domination one step further with their close relatives, the birds, by pushing the rivaling pterosaurs into extinction (and possibly out of the skies altogether - there is some debate as to validity of the claim that Quetzalcoatlus and other Azdarchids could even fly). The only biome the dinosaurs hadn't claimed at that point were the seas. I believe I had provided a good link discussing this sort of thing here: http://www.bbc.com/future/story/20170918-what-if-the-dinosaurs-hadnt-died-out

And did the impact bring about flowering plants or was that due to changes in climate that were already happening?

Angiosperms (or any plant that flowers) have there roots (pun intended  ) way back in the Triassic Period (251.9 million to 201.3 million years ago - the Triassic is the first period of the Mesozoic Era, which ended in the Cretaceous K-T extinction) when dinosaurs were still evolving from small, lizard-like archosauria. They diversified into recognizable species as we might see today in the early Cretaceous around 120 million years ago during the Aptian stage of that period. The point is, dinosaurs were well=adapted to eat flowering plants and their close relatives. Angiosperms did eventually replace conifers as the dominant trees from 100 to 60 millio years ago (from the Cenomanian to the Maastrichtian stage, roughly). This may have influenced dinosaur size and evolution, perhaps reducing overall dinosaur size by a percentage. Certainly such plant-guzzlers like the famous and truly huge long-necked sauropods shrunk somewhat in size after the 100 million year mark, suspiciously correlative with the rise of the angiosperms. The Chicxulub impact at the end of the Cretaceous hit the angiosperms just as hard as it hit the dinosaurs - many species went extinct, and like the dinosaurs - many descendants and derivatives are alive today.

Interesting that there were no ice ages back then and all land was concentrated on one supercontinent.

Yes, there were no ice-ages back then, and significantly less seasonal variance - but this is dependent on the time in question. The entire Jurassic period (the period between the Triassic and Cretaceous) was universally hot and dry, with a wet season/drought season ratio and aaverage temperature 3 degrees Celsius above our current temperature. The poles were ice-free. The super-continent that you are referring to, Pangaea, had already broken up 175 million years ago during the Toarcian stage of the Early Jurassic into the continents of Gondwana (South America, Africa and India), Antartica-Australia, Eurasia and North America. By the end of the Late Jurassic, the world looked like this:


During Early to mid Cretaceous period (roughly 145 million to 100 million years ago), the world entered one of its hottest periods ever, along with an accompanying humidity caused by a further break-up in continents and lowered sea-levels - leading to a tropical atmosphere. The average temperature was 4-6 degrees higher then the global average today. Seasons began to become apparent, though only in certain latitudes - Antarctica and Australia had drifted into the south pole and became trapped in a winter/summer seasonal cyclic rather reminiscent of today's temperate seasons. Dinosaurs, pterosaurs, early-birds and giant amphibians all lived there as they did for millions of years before. Just Google "Antarctic Dinosaurs".

India here split from Antarctica/Australia and migrated north. Africa and South America also separated, and North America was divided by the Western Interior Seaway (also known as the Skull Creek Seaway, or Cretaceous Sea) into to two separate landmasses (Laramidia in the west, and Appalachia in the east) that throughout the period would join and split more then three times, promoting great evolutionary diversity among the dinosaurs that lived there.



Starting at the Coniacian stage of the Cretaceous period (89.8 million years to 86.3 years ago) and continuing until the Campanian stage, the sea levels rose and fell, causing some seasonal chaos. Temperatures did rise as far a 8 degrees above the current maximum, and various marine extinctions took place. The dinosaurs endured and flourished. Then, as the Campanian drew to a close and the Maastrichtian stage began, temperatures stabilized, the sea-levels fell again, and an annual season-cycle much like our own now began. No-where could this be seen more vividly then in North America, which now basically resembled our modern understanding of it (most of the other continents were the same in this detail).





Dinosaurs migrated to WELL above the arctic circle, as the Prince Creek findings prove. Herbivores like duck-bills and horned ceratopsids no doubt sought the rich summer greenery that the temperate seasons provided, with tyrannosaurs and dromaesaurids predators following them.




Okay, I think I've bored you enough - but hopefully you, as well as anyone else who reads this, will gain a better understanding of the complexities of the Mesozoic world.

Wow, wonderful post, Stellarator!  And not boring at all; actually if I hadn't gone down the route of astronomy then I'd very likely have become a geologist instead.  It's fascinating.

midtskogen, no worries.  I was wondering if that might have been the case.  Even so, the association of energy with diameter would still be fair to question.

actually if I hadn't gone down the route of astronomy then I'd very likely have become a geologist instead.

I'm facing the same conundrum in my life right now Wats, I would love to study astronomy and physics in university, but I also really enjoy talking and learning about paleontology. Hmm, maybe I could be an Astropalaeontologist? It certainly sounds neat...

I would love to study astronomy and physics in university, but I also really enjoy talking and learning about paleontology. Hmm, maybe I could be an Astropalaeontologist? It certainly sounds neat...

Consider astrobiology.  It's a fascinating field to get into, and perhaps one of the most multidisciplinary ones as well.  It draws on astrophysics and biology, obviously, but also chemistry, thermodynamics, geology, planetary and atmospheric science.  Even if you don't end up getting a career in it specifically, the training will be applicable in many other areas.

Consider astrobiology.

Yes, certainly. This seems like the general direction I'm going in with my education, as it pretty much encompasses all of my prime interests. Next year I'll be going into university, so all I have to do now is figure out what courses to take, which would no doubt encompass those fields you had outlined .

Wow, wonderful post, Stellarator!  And not boring at all; actually if I hadn't gone down the route of astronomy then I'd very likely have become a geologist instead.  It's fascinating.

midtskogen, no worries.  I was wondering if that might have been the case.  Even so, the association of energy with diameter would still be fair to question.

Yes that was amazing- worthy of Encyclopedia Brittanica!  I also had a fascination with dinosaurs as well as birds growing up, and this was well before I knew they were so closely related.

Genetically, are dinosaurs and birds as closely related as we are to the great apes?  The main difference being of course that birds have feathers and could fly and dinosaurs had scales and could not.

http://forum.spaceengine.org/viewtopic.php?p=24579#p24579 I would love to study astronomy and physics in university, but I also really enjoy talking and learning about paleontology. Hmm, maybe I could be an Astropalaeontologist? It certainly sounds neat...

Consider astrobiology.  It's a fascinating field to get into, and perhaps one of the most multidisciplinary ones as well.  It draws on astrophysics and biology, obviously, but also chemistry, thermodynamics, geology, planetary and atmospheric science.  Even if you don't end up getting a career in it specifically, the training will be applicable in many other areas. [img=24x24]http://forum.spaceengine.org/images/smi ... _smile.png[/img]

Astrobiology that isn't just limited to organic life would be ideal- I have always been fascinated by the possibilities of complex inorganic life.  Remember, computers are made of silicon, which is closely related to carbon 

Consider astrobiology.

Yes, certainly. This seems like the general direction I'm going in with my education, as it pretty much encompasses all of my prime interests. Next year I'll be going into university, so all I have to do now is figure out what courses to take, which would no doubt encompass those fields you had outlined .

I'm so envious lol, I wish I was growing up right now instead of in the late 80s when I went to HS and there were no good astronomy simulations back then.  As a matter of fact I ended up writing my own astronomy program using BASIC on a lowly Tandy 1000 HX that I had with 640K of memory and a floppy drive (no hard drive.)  I did diagrams of all 88 constellations with star colors and magnitudes using Wil Tirion's excellent maps in Astronomy magazine and also wrote a program that shows what size each  planet would appear to be at different magnifications.  I also did a program which calculated the number of days between any two dates, including leap years, using that to graph biocyclic patterns.  None of this was of any commercial value whatsoever- I just did it for fun lol.


Interesting thing I read about the end of the Cretaceous was that land dinosaurs were evolving into warm blooded creatures who took care of their young (and some even gave live births) and had stereoscopic vision and had high intelligence.  If they had continued to evolve intelligent sentient life might have evolved from them (which has been a theory in many sci fi stories.)

as an aside, it's really a shame that humanity is responsible for the sixth mass extinction in the planet's history, one of the species I really would have liked to have seen and which seems like it would be closely related to dinosaurs was the Giant Moa and the Elephant Bird Aepyornis.  Both were gigantic the former was 12 feet tall and the latter laid eggs that were a foot wide.

Genetically, are dinosaurs and birds as closely related as we are to the great apes?  The main difference being of course that birds have feathers and could fly and dinosaurs had scales and could not.

That dinosaurs and birds are related is in no way doubted (well, except by a small minority, who are widely considered to be 'prehistoric' in their thinking ). The main questions are: when did they split and how did this effect their respective evolution? The straight answer would be: yes - dinosaurs and birds were as related to one another as chimps or bonobo apes are related to homo sapiens sapiens - perhaps even more so. After all, you can't really create a chimpanzee from a human fetus like you could a velociraptor from a chicken embryo (err, not that anyone has tried the former, to my knowledge).

You often see the small richly feathered theropod Archaeopteryx lithographica being cited as the "first bird".

The truth is a bit more complex - as we actually do not have fossilized evidence of the "First Bird". Archaeopteryx was discovered in Tithonian stage rocks of the Late Jurassic, dating about 150 million years old. Similar fossils of the species Anchiornis, Xiaotingia, and Aurornis were discovered in the Late Jurassic Kimmeridgian stage deposits of western Liaoning province in China - all dating from over 160 million years ago! The latter specimen, Aurornis Xui, represents our closest link between dinosaurs and true birds.

As you can probably tell, the difference between these creatures and true birds is fairly arbitrary. All are considered avialans - a group that are usually referred to be the earliest form of bird that wasn't an outright dinosaur. It is a slippery term to codify however, and in general could be used as a word describing any avian, be it Aves or Dromaeosauridae theropods. So we can't really justify any distinction between non-avian dinosaurs and avian dinosaurs - there are far too many indiscretions and messy evolutionary records.
Further, LOTS of non-avian dinosaurs had feathers for which ever reasons. Some were just proto-feathers (or "dino-fluff"), like that on the chinese tyrannosaur Yutyrannus Huali (a fine example of a large feathered theropod, an early ancestor to Tyrannosaurus Rex):

But on other dinosaurs like all those of the dinosaur clade Maniraptora (that include the subgroups of Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and Alvarezsauroidea) possessed true Pennaceous feathers (in other words, flight feathers):

The presence of feathers on Velociraptor is beyond doubt, as multiple fossils show:


A skeptic might ask: well, what about bigger dromaesauridae? Surely they wouldn't have feathers like this? Cue the discovery of Dakotaraptor steini, found in a 66 million year old formation in the widely famous dinosaur fossil-site Hell Creek.  AT 5.5 meters (18 feet), it was one of the largest and latest dromaesaurs known. We know that on the ulna bone of their lower arms, large papillae ulnares or quill knobs were present, attachment points for large pennaceous feathers. Adult Dakotaraptor would be much too heavy to fly. And yet the feathers were still present. There is a variety of possible alternative functions for its wings, including shielding of eggs, display, intimidation and keeping balance while pinning down prey with the sickle claw. This goes for the rest of the feathered dinosaurs (it does pay to remember that some small dinosaurs in the Manoraptora like Microraptor Gui could actually fly/glide between trees)

So, after this lengthy detour into avian/non-avian dinosaur relations, a key question still remains: when DID the first true bird actually appear in the fossil record - one that resembles our modern idea of a bird? Well, it would probably be little Confuciusornis, of Early Cretaceous China, found in 120-125 million year old rocks of the Yixian and Jiufotang Formations, dating to the Aptian-Barremian stage roughly. We have many hundreds of fossils of these small creatures, suggesting that they were very wide-spread and successful, at least for Cretaceous Asia:

The fact that these birds did so well in a world were the skies were still ruled by the pterosaurs and the ground coveted by the rapacious raptors is astounding - but they did, as we can now see. They diversified into multitudes of species in the Late Cretaceous - becoming very modern-looking creatures like Hesperornis and Ichthyornis.

I have always been fascinated by the possibilities of complex inorganic life.

Here is an excellent link to an exert of a book discussing this intriguing topic: http://www.xenology.info/Xeno/8.2.3.htm

Both were gigantic the former was 12 feet tall and the latter laid eggs that were a foot wide.

Ever hear of the Terror Birds? Every bird has a dinosaur just waiting to come out.....

[youtube]Ds0aDc6sBtg[/youtube]

Anyway, I would like to add that birds were one of my greatest passions way back when as well A-L-E-X!. As a child, bird-watching was my favorite outside activity, and I would spend many hours filming any avians I could find on my folks old camera. Since then, I've raised many birds - including a wild Starling and even a foundling bald eagle! But those are stories for another time...