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| date | 2000-11-24:15:49 |
| SelfConciousness | I've been reading bits of other people's journals notice I tend to use mine more for "thinking out loud" than great feats of self-revelation. This is what I am. This is what I do. These are the things that interest me. Sit me down in a pub and this is the kind of stuff I'll talk about. Physics, metaphysics, nature, poetry, what I'm reading, movies I've seen, and fun projects I'm either involved in or have been involved in or would like to be involved in. And rather than just sketching a few lines of an idea, I like to flesh it out more, to explore its ramifications and possibilities in detail. |
| Creatures |
Several million black gray squirrels were out today at noon, foraging in a neighbor's yard for nuts and stuff. There must be a particularly nice tree there. Why is it that individuals of species named after colors never match the color in the name? Gray squirrels are black as often as not. Black bears are frequently brown and in one locale white. Blue jays are blue, but not as blue as Stellar's jays. You'd think that after a while people would figure out that naming animals after the color of a few individuals is a bad idea, because color is highly plastic because it is pretty simple, biochemically speaking, to change and it must be selected for pretty heavily due to its role in attracting attention, both positive and negative. It's only recently, though, that micro-evolutionary variation--see The Beak of the Finch, for example--has been recognized as an continual shaper of the average characteristics of a species, so I guess I shouldn't blame the early taxonomists, who had a tough enough time without my latter day criticisms. |
| Play |
This should probably have a category of its own, but I think of it as play, because most of what I do or plan to do with the kids I think of as play. Somewhere in North America, on the eastern slopes of the southern moutains, perhaps looking out over the Mojave, there are heaps of dead dinosaurs. I want to go find them. So does Alex, my older child. It'll be a few years before he's old enough, but it's never too early to start planning. The story goes like this. Everyone I've told about this disbelieves it, explaining carefully things I already know. I think the core of their disbelief is just the idea that on the timescale of 65 million years, the idea of finding something that you can identify as having died on one particular day just bothers people. But you can. As follows. We know that the dinosaurs were killed by the a giant impact, probably cometary, probably on the Yucatan Penninsula. We know this for a couple of reasons: there is an irridium-rich layer at the K-T boundary, which is the geologic interface that separates strata that contain dinosaur fossils from those that don't. Irridium is a rare-earth metal, so called because they are rare. As it happens, irridium is pretty abundant in some non-terrestrial objects, like asteroids and (probably) the stony/metal core of comets. We also know that there is an impact crater of the right size and age at the tip of the Yucatan Penninsula, and by looking at the size the crater (which gives an estimate of the size of the object) and the amount of irridium in the K-T boundary, we can estimate the ratio of irridium to total mass of the impacting object. The ratio is pretty small, as these things go, so it is likely that it was a cometary impact rather than an asteroidal one, because comets are mostly ice and so have a lower irridum-to-total-mass ratio than asteroids. I think we can all agree that any dinosaur standing directly at the point of impact was probably killed instantly. We can also agree that dinosaurs living on the far side of the world might have lived for a long time afterwards. But think about what happened in between. The impact was powerful enough to splash molten rock hundreds of kilometers into the sky, to vaporize quite a lot of water and to send enormous waves sloshing up the shallow sea that covered central North America. A wall of super-heated air would have gone howling out from the point of impact, flash-frying any dinosaur in its path for hundreds, possibly thousands of kilometers. That wall would move fast, close to the speed of sound (330 m/s) so within minutes it would be killing things hundreds of kilometers away. Think about it in terms of a series of concentric rings around the point of impact--everything in the innermost ring would be completely obliterated. But far enough away there would be a ring where everything was killed within a few seconds, but not much else happened. The plant life would burn, probably, killing any survivors. Then the material splashed from the impact would begin to fall. And finally, near the coast, the waves would arrive, churning everything up, depositing a layer of mud over the remains. It seems to me that these are nearly ideal conditions for fossilization: there should have been a fairly broad zone in which nearly everything was killed, and then covered with what is basically volcanic ash, and then possibly covered with mud. So if there were any herd dinosaurs in this zone, they will all have been killed and fossilized together. This is the important thing. Because of the extreme spatial and temporal proximity of their deaths, and the absence of scavengers (which would also mostly have been killed) if one member of a herd was fossilized, then it's quite likley they all would be. Ergo: heaps of dead dinosaurs. Maybe this is a wild dinosaur chase. But it sounds like fun, something to do in five or six years, when Alex is old enough to go on a serious field expedition in some pretty wild places. |