# Dinosaurs and Treetops **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [September 3, 1999, 1:55pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867 "1999-09-03T13:55:00Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 2, 2000, 8:26pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/41 "2000-03-02T20:26:00Z")
[“Scientists Discover Fossil Bones of What May Be the Biggest Dinosaur that Ever Lived”](http://www.abcnews.go.com/sections/science/DailyNews/dinosaur_000120.html) They did not find all the bones (They seldom find them all), so they can only estimate its length: _157_ to _167_ feet, more than half the length of a football field, halfway from home plate to the outfield fence in most ballparks. The _Discover_ article referred to earlier MAY be this one: [www.britannica.com/bcom/magazine/article/0,5744,48320,00.html](http://www.britannica.com/bcom/magazine/article/0,5744,48320,00.html) It discusses recent findings in Argentina and reveals that no one is certain why dinosaurs that lived in the Southern Hemisphere seemed to have been larger than the ones from up north. Remember too, that the continents were different then. with Laurasia in the north and Gondwanaland in the south. (When you search the Britannica website, it finds its own entries, PLUS relevant magazine articles and other websites, AND it recommends books which can be purchased from Amazon. It found several _Discover_ articles about dinosaurs and this seemed like the one everyone else was talking about earlier. But withou the title of the article, I could not be sure.) * * * \>\ \_ **L\_\_\_L** ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 2, 2000, 8:55pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/42 "2000-03-02T20:55:00Z")
> [@](#): > > Originally posted by Momotaro: > **First, about the sauropod’s neck. Yes, the reference is in a Discover magazine from about a year ago but I can’t find it because I’m stranded in a foreign country. It shouldn’t be hard to find, there’s a big sauropod’s (four-legged, long-necked dinosaur’s) skeleton on the cover.** Here’s the article you mentioned: [www.britannica.com/bcom/magazine/article/0,5744,28765,00.html](http://www.britannica.com/bcom/magazine/article/0,5744,28765,00.html) It describes how paleontologists are using computers to create virtual dinosaurs to see how they moved. (Ignore the thumbnail cover in the upper right corner depicting a radio telescope. They use that same cover on all _Discover_ articles. The articles are also lacking the illustrations, but, curiously, they include the _captions_ that went with them.) > [@](#): > > No animal at the time of dinosaurs approached the size of the blue whale. See my post above. * * * \>\ \_ **L\_\_\_L** ---
**Author:** ![system](https://global.discourse-cdn.com/straightdope/original/2X/e/e489c3b7d8fce19c4b355dd4fc3f88cc39c34b87.png) [@system](https://boards.straightdope.com/u/system)\ **Post date:** [March 2, 2000, 11:50pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/43 "2000-03-02T23:50:00Z")
I was going to suggest this thread (or at least the divergent argument on “growing earth”) should head to GD so we don’t get a repeat of the 360 deg in a Circle/Velikosky debate thread, but Jill said it’s okay… 😉 speakeasy said: > [@](#): > > Mammals don’t grow that big because we are a higher energy density form of life. Your average mammal can increase it’s heat and work output by a factor of 10 from resting to full boogie. The problem for us types is getting rid of the heat. On land, elephants are about the limit. People do it better than most types of animals, even other mammals. Speakeasy, Cecil did address that point. That’s the details of the warm-blooded vs. cold-blooded argument. Along those lines, I saw a Discover article some time before the previously mentioned one that discussed whether dinosaurs were warm or cold blooded, and whether that mattered. Some research indicates that they may have been cold blooded, but had certain features that duplicated the warm-blooded animals, so they were better at energy output than modern reptiles. Not that I recall the details. I think Artboy answered the main question from the original article. They were big because of an abundant food supply. That does beg the question of why dinos beat out mammals until the K-T extinction. CKDextHavn commented: > [@](#): > > \<\< but the Encyclopædia Britannica places the origins of dinosaurs between 230 and 235 million years ago. \>\> > > Before or after lunch? I didn’t follow. What? Ray14dot4 said: > [@](#): > > I can see I landed in a nest of nitpickers. Next time I’ll make my historical analogy anal retentively exact. Ray, this thread is your first entrance to this site. You apparently haven’t lurked here, or you would be aware that (a) this site is full of nitpickers; (b) the mating call of the looney is to invoke Galileo (or Einstein, or Einstein and Galileo in a tag team match). > [@](#): > > Tom, no one said “matter leaping into existence (only in the center of a planet?)” It is a universal process. Stars are near the end of the process (guess what happens to the mass of a star that makes it implode). The Earth near the beginning. > Jupiter could be said to be near the middle since it has characteristics of a brown dwarf. Ugh. Auraseer has addressed the star comment. I just like the way you are implying that the Earth will evolve into a Jupiter, then a brown dwarf, and finally a star. Plus, Jupiter is \not\ a brown dwarf - it is much too small. more from Ray14dot4: > [@](#): > > Also, it seems to me that in order for a massive star to become a black hole it would have to be ADDING more mass until the point of implosion. Otherwise it would ALWAYS have been a black hole. The original theory was that no energy could escape from a black hole. But now we know that they emit enormous amounts of radiation. And so on. And > [@](#): > > If sufficient dust (mass) collects to form a star large enough to become a supernova why does the supernova have to undergo an explosion before it can implode and become a black hole? If it is burning up it’s “fuel” it should losing mass and never become a black hole. If it had sufficient mass from beginning it should have become a black hole instantly. > I submit that the nuclear creation of matter in the core of the star causes it’s mass to increase to the point where it explodes and then collapses. A similar nuclear reaction is taking place in our earths core. No, you are greatly mistaken. The reason the star must go supernova after burning off a lot of mass and throwing off more mass in the supernova, but then has enough mass to form a black hole, is because \it contracts\. If you squeeze the mass of the earth into the size of a pinhead, you will get a black hole. (I’m not saying that is a possibility - that’s an exaggerated visual.) We’re talking \density\, not just \total mass\. Think of it this way - in the Earth’s sky there are lots of clouds of water and dust. One cloud weighs more than a 747. How does it stay aloft? Because it is spread over a much greater volume, so the density is low. Same thing with star mass. The matter is held apart by the internal heat and nuclear forces while the gravity holds it together, in a balancing act. When the star goes supernova, the heat is dissapated, and the mass collapses under the pull of gravity without the energy to hold it apart. Then it collapses into a much smaller volume, and thus forms the black hole. > [@](#): > > One look at a volcano or earthquake (especially in the Pacific Ocean) tells me our Earth is a producing massive amounts of energy/matter. If our planet’s core was just an inert mass of molten rock and iron one would expect it to be cooling not erupting. (Maybe we would be experiencing global cooling not warming?) 1. The Earth is cooling. It is just a slow process, because the molten core generates heat that slows the process. 2. The heat is generated through radioactive decay and by friction (turbulence) caused by internal mixing. Also perhaps there is a dynamo effect. 3. Lava flowing up from the core is not spewing out because there is an increase in matter. Yes, it is under pressure - gravity and thermal pressure. 4. “Global warming” is not related. Giantrobo said: > [@](#): > > Cro-Magnon?! Cro-Magnon are vastly different then modern man. Once modern man moved into Cro-Magnon territory the Cros disappeared. Therefore useing Cro-Magnon to compare modern man against is a flawed argument. We are not decendents of Cro-Magnons. I believe you are confusing Cro-magnons with Neanderthals. From [http://www.talkorigins.org/faqs/homs/specimen.html](http://www.talkorigins.org/faqs/homs/specimen.html) > [@](#): > > “Cro-Magnon Site”, Homo sapiens sapiens (modern) Discovered by workmen in 1868 at Cro-Magnon in France. Estimated age is 28,000 years. The site yielded skeletons of about half a dozen individuals, along with stone tools, carved reindeer antlers, ivory pendants, and shells. The Cro-Magnons lived in Europe between 35,000 and 10,000 years ago. They are virtually identical to modern man, being tall and muscular and slightly more robust than most modern humans. They were skilled hunters, toolmakers and artists famous for the cave art at places such as Lascaux, Chauvet, and Altamira. And [http://www.talkorigins.org/faqs/homs/species.html](http://www.talkorigins.org/faqs/homs/species.html) [quote] \Homo sapiens neanderthalensis (was Homo neanderthalensis)\ Neandertal man existed between 230,000 and 30,000 years ago. The average brain size is slightly larger than that of modern humans, about 1450 cc, but this is probably correlated with their greater bulk. The brain case however is longer and lower than that of modern humans, with a marked bulge at the back of the skull. [snip] \Homo sapiens sapiens (modern)\ Modern forms of Homo sapiens first appear about 120,000 years ago. Modern humans have an average brain size of about 1350 cc. The forehead rises sharply, eyebrow ridges are very small or more usually absent, the chin is prominent, and the skeleton is very gracile. About 40,000 years ago, wi ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [March 2, 2000, 11:54pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/44 "2000-03-02T23:54:00Z")
Great. I run that sig line and screw up my formatting. ---
**Author:** ![Loren\_Pechtel](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@Loren\_Pechtel](https://boards.straightdope.com/u/Loren_Pechtel)\ **Post date:** [March 3, 2000, 9:55pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/45 "2000-03-03T21:55:00Z")
Ray14dot4: It appears that my clock has more brains than you. When I followed that link to see what you were talking about, it spoke up “coo-koo”. I didn’t waste my time reading the whole thing, but I did see enough to see it doesn’t work. First, it’s attacking the lack of plate tectonics on any body we can see the surface to be able to tell if there are plate tectonics. Of course we see no plate tectonics–all such bodies are far smaller than Earth, their radioactivity won’t be enough to maintain a molten core. Second, the pictures supposedly showing expansion: Consider an airless body like the moon. There’s very little to wear down the features. Therefore, there should be numerous great rifts as deep as the structual strength of the rocks permits. When we look at the moon, we see craters, not rifts. Third, without subduction, how do you explain metamorphic rock? What takes surface rock down many miles to the point it’s deformed by heat? Fourth, plate tectonics tells oil men where to drill. If the theory is no good, why do they find oil? ``` To address some of your other points on here: The reason stars don't simply start out as black holes is that they start out a diffuse mass of gas. As it collapses, it gets hot enough to support fusion. That heat keeps it from collapsing further, until it runs out of fuel. As for the mass loss due to fusion--it's about 1% of the material actually fused (not the entire star except in the case of tiny stars). It's not going to have a big effect on whether it can reach a black hole state or not. ``` ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 3, 2000, 11:10pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/46 "2000-03-03T23:10:00Z")
> [@](#): > > Originally posted by JillGat: > \*\*I never had wisdom teeth. > Jill > more highly evolved. > \*\* Ah, but are you lactose tolerant or INtolerant? According to [www.talkorigins.org/faqs/mutations.html#Q2](http://www.talkorigins.org/faqs/mutations.html#Q2) , lactose tolerance is a recent mutation. Our distant ancestors were originally lactose intolerant; this encouraged the weaning process. But our more recent ancestors got the bright idea to raise certain animals for milk when they realized they produced more milk than any woman ever could. If you are lactose tolerant, it’s a good chance you’re descended from dairy farmers or goat-herders and shepherds. > [@](#): > > It should be understood that it was a matter of chance that the lactose tolerance mutation appeared in a group where it was advantageous. It might have been established first by genetic drift within a group which then discovered that they could use milk. In other words, some daring person who already had the mutated gene tried cow’s milk and found it could sustain him or her and got the idea to capture and raise these animals for their milk. My mother is one-quarter Cherokee. American Indians, with some exceptions, did not drink animal milk. They used their hides, meat and bones, but rarely did they keep them for milk. (Perhaps they would in emergencies, such as the death of a mother, in order to save her baby.) I’m betting they were lactose intolerant, which would explain why my mother is and why I and my two brothers are as well. Correct me if I’m wrong, please. As for why dinosaurs got so big, I’d go with the theory of abundant plant life leading to big herbivores (and higher oxygen levels) which in turn led to big carnivores. The Earth’s climate seems to have undergone a radical change (caused by continental drift, perhaps) some time in the Cretaceous which led to the proliferation of flowering plants which can endure more radical changes in temperature than non-flowering types. Then there would have been less food for the herbivores, which meant less food for the carnivores, which meant the dinosaurs were already on the decline when that asteroid or comet hit the Yucatan. I think that’s what Robert Bakker says, anyway. * * * When all else fails, ask Cecil. ---
**Author:** ![Jois](https://avatars.discourse-cdn.com/v4/letter/j/ea666f/32.png) [@Jois](https://boards.straightdope.com/u/Jois)\ **Post date:** [March 3, 2000, 11:46pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/47 "2000-03-03T23:46:00Z")
Cheese, man, cheese. If you are lactose unevolved you are supposed to be able to tolerate cheese. Much better to have cheese than just use milk for bathing. I can’t remember about butter, it may also have been a use for butter for the lactose unevolved. Jois ---
**Author:** ![\_Df](https://avatars.discourse-cdn.com/v4/letter/_/7ba0ec/32.png) [@\_Df](https://boards.straightdope.com/u/_Df)\ **Post date:** [March 18, 2000, 12:50am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/48 "2000-03-18T00:50:00Z")
Giantrobo said: “The reason why Dionsaurs are so big is more simple than everyone thinks.” Your reasoning aside, this does raise a critical point: namely, beware the terrible Celine Dionsaur! Uggh! > [@](#): > > The Discover article…discusses recent findings in Argentina and reveals that no one is certain why dinosaurs that lived in the Southern Hemisphere seemed to have been larger than the ones from up north. I would think it obvious - tidal forces. Centrifugal force may have weakened the effective force of gravity, but it was _not_ the only force acting. Remember that the earth is tilted on its axis, and it turns out that the south pole is farther from the sun at aphelion and closer at perihelion. And that’s clearly the same thing as saying that the path it follows is more elliptical than the path the north pole follows. And that then equals greater tidal forces: stronger attraction by the sun during southern summer, and stronger centrifugal forces trying to fling the dinosaurs into the outer solar system during southern winter. _Et viola_! Bigger biggies. But I do have one lingering doubt. Doesn’t the fact that I had three wisdom teeth, while making me less [_evolved_ than Jill, still make me _wiser_? (I had one wisdom tooth removed, and believe me, the difference was immediatley noticeable!) ---
**Author:** ![Fillet](https://avatars.discourse-cdn.com/v4/letter/f/2acd7d/32.png) [@Fillet](https://boards.straightdope.com/u/Fillet)\ **Post date:** [March 18, 2000, 1:31am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/49 "2000-03-18T01:31:00Z")
{:-Df said: {QUOTE]I would think it obvious - tidal forces. Centrifugal force may have weakened the effective force of gravity, but it was not the only force acting. Remember that the earth is tilted on its axis, and it turns out that the south pole is farther from the sun at aphelion and closer at perihelion. And that’s clearly the same thing as saying that the path it follows is more elliptical than the path the north pole follows. And that then equals greater tidal forces: stronger attraction by the sun during southern summer, and stronger centrifugal forces trying to fling the dinosaurs into the outer solar system during southern winter. Et viola! Bigger biggies. [/QUOTE] Please tell me you’ve been overcome by the need to spread a bit o’ blarney on this day… ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 18, 2000, 10:32pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/50 "2000-03-18T22:32:00Z")
Someone correct me if I’m wrong, but i once heard that the Earth would have to rotate REALLY fast in order for centrifugal force to cancel out some of the force of gravity. I think we’d have to have five-hour days. And that’s assuming that such a high rate of rotation wouldn’t rip the Earth to pieces or prevent it from forming in the first place. * * * When all else fails, ask Cecil. ---
**Author:** ![Loren\_Pechtel](https://avatars.discourse-cdn.com/v4/letter/l/d2c977/32.png) [@Loren\_Pechtel](https://boards.straightdope.com/u/Loren_Pechtel)\ **Post date:** [March 19, 2000, 1:46am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/51 "2000-03-19T01:46:00Z")
> [@](#): > > Originally posted by jab1: > \*\*Someone correct me if I’m wrong, but i once heard that the Earth would have to rotate REALLY fast in order for centrifugal force to cancel out some of the force of gravity. > > I think we’d have to have five-hour days. And that’s assuming that such a high rate of rotation wouldn’t rip the Earth to pieces or prevent it from forming in the first place. > \*\* ``` It would have to be a lot less than 5 hours. Consider, synchronous orbit is where going around once a day keeps something in orbit. And what is orbit other than the point where the centrifugal force is equal to gravity? Therefore, to find the day length to cancel surface gravity (at the equator), look at low-Earth orbital periods--something like 80 minutes. The actual value would be slightly less, as it's a few miles closer in. As for it's ripping Earth apart--it wouldn't be *QUITE* powerful enough to do that. However, loose objects at the equator would not be held down--they would be prone to departing. The worst casualty would be the atmosphere--it would be flung off *VERY* quickly. The oceans would go with it. On the lifeless ball that remained, things like volcanoes would toss rock into space. ``` ---
**Author:** ![Boris\_B](https://avatars.discourse-cdn.com/v4/letter/b/fbc32d/32.png) [@Boris\_B](https://boards.straightdope.com/u/Boris_B)\ **Post date:** [March 19, 2000, 7:58am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/52 "2000-03-19T07:58:00Z")
Well, I’ll go out on a limb and say that the centrifugal force idea Murphy came up with in the column isn’t ridiculous. Centrifugal force from Earth’s rotation _does_ offset gravity somewhat, everywhere except at the poles. Sure, it may not be significant; it might be one percent or one ten thousandth of one percent. Significance is in the eye of the beholder. If you want to say it would only be significant if days lasted eight hours, that’s a perfectly acceptable definition. I guess I don’t know why Adams or anyone else thinks this is such a stupid idea. Earth spins slower now than it used to; sure, it hasn’t been a significant speed decrease (eye of the beholder). Days _have_ been getting (insignificantly) longer and non-polar weights (insignificantly) greater. Until you calculate the amount the Earth has slowed, you wouldn’t know this. My point is, Murphy had the _principle_ correct, and can be forgiven for guessing the _degree_ incorrectly. * * * What part of “I don’t know” don’t you understand? ---
**Author:** ![Boris\_B](https://avatars.discourse-cdn.com/v4/letter/b/fbc32d/32.png) [@Boris\_B](https://boards.straightdope.com/u/Boris_B)\ **Post date:** [March 19, 2000, 8:03am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/53 "2000-03-19T08:03:00Z")
As to the argument about Cro-Magnon … here’s a link I hope will clear things up: [http://www.emi.net/~bs-soft/Cro-Magnon.html](http://www.emi.net/~bs-soft/Cro-Magnon.html) > [@](#): > > The name Cro-Magnon is now generally employed in referring to all such anatomically modern humans found in Europe and the Middle East, from their rather sudden appearance about 40,000-30,000 years ago… the Cro-Magnons … are classified as Homo sapiens sapiens. Cro-Magnons are a temporally distinct group of people, not a genetically distinct group of people. ---
**Author:** ![OliverTwistofLime](https://avatars.discourse-cdn.com/v4/letter/o/b487fb/32.png) [@OliverTwistofLime](https://boards.straightdope.com/u/OliverTwistofLime)\ **Post date:** [March 19, 2000, 9:28am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/54 "2000-03-19T09:28:00Z")
I have nothing to add except that this was a fascinating thread to read and I compliment those who spent the time and energy to produce the responsible material. * * * Don’t ever say _288_ in polite company. Its just two gross! ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 19, 2000, 11:29pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/55 "2000-03-19T23:29:00Z")
> [@](#): > > Originally posted by Boris B: > \*\*I guess I don’t know why Adams or anyone else thinks this is such a stupid idea. Earth spins slower now than it used to; sure, it hasn’t been a significant speed decrease (eye of the beholder). Days _have_ been getting (insignificantly) longer and non-polar weights (insignificantly) greater. Until you calculate the amount the Earth has slowed, you wouldn’t know this. My point is, Murphy had the _principle_ correct, and can be forgiven for guessing the _degree_ incorrectly. > \*\* I’m not so sure. That would be like saying, “We can fly to the moon!” “All right!” “And the trip will take only ten minutes!” “Uh, wait a minute…” We know the days were shorter in the past by counting the rings of fossil corals. The days get progressively longer the younger the coral fossil is: Days per year - Years in the past 435 Days - 850 Million Years Ago 401 Days - 395 MYA 387 Days - 300 MYA 382 Days - 190 MYA 381 Days - 180 MYA I got this from a _Creationist_ website: [www.creation-answers.com/time4.htm](http://www.creation-answers.com/time4.htm) While they accept the evidence that days were shorter in the past, they are skeptical the coral samples really are as old as the carbon-dating indicates. :rolleyes: So take their OTHER findings with a grain of salt. * * * When all else fails, ask Cecil. ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 19, 2000, 11:49pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/56 "2000-03-19T23:49:00Z")
In my haste, I neglected to finish my post! :o As you can see, the year was only _16_ days longer 180 million years ago when the dinosaurs were really enormous. Sure, it means the Earth was rotating faster then, but not enough to counteract the force of gravity enough to make them weigh less. I just did a rough calculation. Assuming the Earth took the same number of hours (8760) to orbit the Sun back then (And there is no good reason to assume that it did NOT), then a day was a bit less than 23 hours long, no more than an hour shorter than today. So a ten-ton dinosaur would’ve weighed 9.99995 tons? 🙂 Oh, and the main reason the Earth’s rotation is slowing is because it’s dragging the moon around with it. If the moon were less massive or it did not exist at all, the Earth’s days would be much shorter. (I wonder how you’d design a 23-hour clock…? “High Noon” at 11:30?) * * * When all else fails, ask Cecil. ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 20, 2000, 12:43am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/57 "2000-03-20T00:43:00Z")
> [@](#): > > Originally posted by jab1: > **skeptical the coral samples really are as old as the carbon-dating indicates.** I made a mistake. You can’t use radio-carbon dating to determine the age of fossils that are 850,000,000 years old. Other methods must be used. * * * When all else fails, ask Cecil. ---
**Author:** ![Fillet](https://avatars.discourse-cdn.com/v4/letter/f/2acd7d/32.png) [@Fillet](https://boards.straightdope.com/u/Fillet)\ **Post date:** [March 20, 2000, 4:34pm UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/58 "2000-03-20T16:34:00Z")
> [@](#): > > We know the days were shorter in the past by counting the rings of fossil corals. The days get progressively longer the younger the coral fossil is: > > {snip} > > I got this from a Creationist website: [www.creation-answers.com/time4.htm](http://www.creation-answers.com/time4.htm) While they accept the evidence that days were shorter in the past, they are skeptical the coral samples really are as old as the carbon-dating indicates. So take their OTHER findings with a grain of salt. Actually, the estimates for length of day and year back in the Precambrian were not originally derived from corals at all, because corals don’t make their first appearance until the Paleozoic - this is a misunderstanding on the part of the person who compiled that information. The biogenic structures actually used are called stromatolites: these are layered buildups created by the binding and trapping of sediment by thin layers of cyanobacteria (“blue-green algae”). Geoscientists used to think that these layers accumulated on a daily basis. Nowadays, the growth patterns of stromatolites is considered somewhat speculative, and length-of-day estimates are made instead from tidal rhythmites, which are (as their name suggests) deposits that reflect the comings and goings of tidal currents in estuaries. (They are considered more reliable indicators of time because they form via completely inorganic processes, so one doesn’t have to worry about the vagaries of biological organisms.) Tidal rhythmites are much rarer than stromatolites in the Precambrian, but enough of them exist to confirm that the length-of-day around 800 million years ago was on the order of 18 hours. The creationist web site is correct in pointing out that the rate of angular momentum transfer from the Earth to the moon (= rate of lunar retreat = slowing of Earth’s rotation rate) has not been constant over geologic time. To my knowledge, no one’s come up with any real workable solutions to this particular puzzle. P.S. on dating methods - radiocarbon dating works reliably on organic materials to 30,000 years ago, less reliably to 45-60,000 years ago. Dating of older sequences (\> 500,000 years) generally relies upon U/Pb, Pb/Pb, K/Ar, or Ar/Ar, depending on the type of material to be dated. ---
**Author:** ![jab1](https://avatars.discourse-cdn.com/v4/letter/j/ee7513/32.png) [@jab1](https://boards.straightdope.com/u/jab1)\ **Post date:** [March 21, 2000, 1:36am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/59 "2000-03-21T01:36:00Z")
> [@](#): > > Originally posted by Fillet: > \*\* Actually, the estimates for length of day and year back in the Precambrian were not originally derived from corals at all, because corals don’t make their first appearance until the Paleozoic - this is a misunderstanding on the part of the person who compiled that information.\*\* Well, to be fair, I made that same mistake, though I DID think 800,000,000 years ago was too far back for something as complex as corals. Should’ve said so, though. > [@](#): > > **The creationist web site is correct in pointing out that the rate of angular momentum transfer from the Earth to the moon has not been constant over geologic time. To my knowledge, no one’s come up with any real workable solutions to this particular puzzle.** But any unsolved problem is evidence for the invisible hand of God, remember? 😉 > [@](#): > > **U/Pb, Pb/Pb, K/Ar, or Ar/Ar** Lessee… U/Pb = Uranium/Lead K/Ar = Krypton/Argon Right? (It’s been a while since I looked at the Periodic Table.) * * * When all else fails, ask Cecil. ---
**Author:** ![Fillet](https://avatars.discourse-cdn.com/v4/letter/f/2acd7d/32.png) [@Fillet](https://boards.straightdope.com/u/Fillet)\ **Post date:** [March 21, 2000, 2:19am UTC](https://boards.straightdope.com/t/dinosaurs-and-treetops/867/60 "2000-03-21T02:19:00Z")
Whoops, sorry, I should’ve written these out in the interests of full disclosure. 🙂 (note to self: got to get out of the office more) U/Pb = uranium-238/lead-206 Pb/Pb = lead-207/lead-206 K/Ar = potassium-40/argon-40 Ar/Ar = argon-40/argon-39 There are a bunch of other decay series that can be used for dating, but these are the most common. Rb/Sr (rubidium-87/strontium-87) was also used a lot in the past, but because it tends to give fairly large error limits it’s not used much anymore. [Previous page](https://boards.straightdope.com/t/dinosaurs-and-treetops/867.md?page=2) [Next page](https://boards.straightdope.com/t/dinosaurs-and-treetops/867.md?page=4)