Subject: The 'sudden' appearance of multicellular life ...
Author:
Posted on: 2009-06-17 21:23:00 UTC
... in the fossil record.
And if I got into the reasons I had to put 'sudden' in quote marks, we'd be here all decade :D
I know it's been asked before, and the recent Board Survey asked in terms of range, but a recent conversation with Sara and that thread about posting below has made me wonder.
So, if you guys don't mind, care to tell me how old you are? I know, as a point of fact, that most people here are in their teens, but I tend to forget, sometimes, and I'm curious.
I'm twenty-two, if anyone cares to know. *waves her Old Lady Walking Stick*
And I started posting here when I was 14. Yikes.
But I keep forgetting!
...in years, anyway. In cynicism, about two hundred. ;)
Not too old, not too young. Just right.
I'll leave it to you to decide whether that's centuries or life-ages of the universe.
But with a bad habit of answering 16. It probably doesn't help that I look around 14, but isn't a useful habit when you're being ID'd (even when it's for child tickets on the train).
But considering I also have an OAP bus pass in my wallet... (the disabled one is the same as the OAP one, so I have to endure).
Hee. Hee hee.
Sorry, I don't give out my age, if possible. (It's a privacy habit I uphold.) But I am within the age range of 1-100. More specifically, the age range of 10-20. *shrugs*
*Az sticks out her tongue in an ever-so-mature fashion*
And I've only got till October till I'll be twenty-one.
Bah.
July 12, that is. I guess I'm about average.
I turn sixteen in August. Suddenly I feel very young. *staring around at all twenty-year-olds*
And a half (almost).
My birthday's in about a month.
32
Nineteen in... about three months.
I turned 21 on April 13th! :D
Hitting 21 in a couple of months, actually. Fun.
As of April 30th.
Who's old now? :P
Party's on the other board. Happy birthday Krisprolls!
January 4th, 1991.
I have been known to tell people I'm anything from 21-24 and then scratch my head, think, try to remember which year I was born in, and then on occasion have to ask what year it *is*...
I forget too. It tends to take me up to six months to remember that we've changed year if I'm writing down a date. This year was odd though. I memorised it in two days. Crazy.
... I'd just spent five hours in the lab drawing specimens, and I came back up to my office, and someone, randomly, asked me how old I was, and I said '22. No, wait, I might be 23 ...' and my friend helpfully said 'Well, what year were you born?'
ME:'...'
FRIEND: '1985? 86? 87?'
ME: '... what year is it?'
FRIEND: '...'
ME: '... *little voice* I could draw you a diagram of the bivalve heterodont hinge if you like?...'
I think there's only a finite amount of space in any one brain, that's my theory. And that just happened to be the bit that got pushed out that day.
I have a horrible tendency to have a similar conversation on those rare occasions when I get IDed. My automatic response tends to be "Dunno, what year is it?"
... tell myself we're in the Century of the Anchovy.
I keep thinking we're still in the Century of the Fruitbat.
We're in the Anchovy now.
... on a slightly more serious note, what century ARE we in? As in, what Earth century, not what Disc century?
It's one of those ones that starts with a two. I think. Holocene, isn't it?
the Common Era calendar (aka the calendar based on when that Jesus bloke was around, but more politically correct).
It is? Since when? Where the hell did the twentieth bugger off to? I'd swear it was here just a moment ago...
I feel sorry for you. I have that trouble too, but I've never forgotten my age or the year (once memorised). Maybe you should carry your birth certificate/passport everywhere with you?
If I'm honest, I just have issues with periods of time shorter than ten thousand years.
Uncyclopaedia tells the truth when it says 'One of the main difficulties in communicating with geologists is their belief that a million years is a short amount of time and their heads are harder than rocks. Consequently, such abstract concepts as "Tuesday Morning" and Lunchtime are completely beyond their comprehension. (This difficulty generates problems particularly when dealing with the girlfriend/boyfriend/spouse and attempting to explain why you were "gone for so long" or why something is taking "so long to occur.")'
Yeah, you've infected me with that, you know. A book I was reading the other day, probably Mutants, mentioned a thousand million years ago. Think they were talking about Hox genes. And I thought "a thousand million? That's... not all that long, is it?"
Not when you consider the Earth itself is 4.6 billion years old ... :D
It wasn't until I remembered how long ago the... Cambrian explosion, is it? was, that I realised, yeah, a thousand million years is actually quite a long time.
Life hasn't been around all that long in the scheme of things :D
... in the fossil record.
And if I got into the reasons I had to put 'sudden' in quote marks, we'd be here all decade :D
as long as I can play Left 4 Dead while you're talking. I'm also a fairly decent multitasker. Woo!
Okay, right. Where to start. I'm simplifying this, uh, a bit.
The record of life through time is the fossil record. The fossil record is things that are preserved in rock. Rock gets laid down in a number of ways and at varying speeds. Sometimes you'll get three inches depth of sediment over a million years. Sometimes you'll get thirty feet. Sometimes you'll get three hundred feet.
Rock also gets destroyed in a number of ways. The longer a given body of rock has been around, the more likely it is to get destroyed soon. There are very few places on the Earth where unaltered rock from, say, the Archaean, are preserved.
The period of time of interest to us is the base of the Cambrian, 542 million years ago (Ma). This is, I'm sure you can appreciate, quite some time ago, even to those of us who work with deep time (for reference, the dinosaurs died out 65 million years ago, human ancestors arose around about 4-3 million years ago ish (this is another one of those 'controversial' issues), etc etc).
Unaltered Cambrian rock (by 'unaltered' I mean not squeezed to hellandgone by more rock on top, not baked by heat and depth, and outcropping at the surface - i.e., rock we can get at) is not actually that common. Most of it has been metamorphosed, subducted or eroded by now. So, baseline for understanding here is that the history of life through time is a book, and the closer to the beginning of the book we get, the more pages are missing.
Now, let's get back to that thing about sediment getting deposited over time.
Evolution happens over time. How much time is debatable (see 'Dawkins vs Gould' by Kim Sterelny for a good synopsis of the two sides of the debate on this one), but for the purposes of right now, we'll just accept 'a long time' and move on. So any given population of animals or plants changes by very small increments (okay, okay, there are exceptions, I'm not going into them here, just work with me).
Not all animals are preserved in the fossil record. Off the top of my head, I think the preservation rate is somewhere between one and ten percent of any given species may enjoy the luxury of fossilisation. It's all dependant on the environment they die in and a few other things. The great majority of fossils that are found are of marine organisms, because the environment is better for preservation under the sea.
So, we have basically a roulette here. Not many specimens are preserved. The rock they're preserved in is becoming increasingly rare. The ones that are preserved are not necessarily the ones that show any kind of easy-to-see change.
And there's one more thing. Generally, the only bits of an animal that fossilise are the hard parts - shells, teeth, bones. But I bet you can think of a dozen things alive today that don't have any of those.
This is where the term 'Cambrian Explosion' comes in. At about 542Ma, suddenly in the rock record we find multicellular organisms with shells. It's literally, bang, there in the rock. Like an invisible line - below it, only microfossils, if that. Above it, shellfish (not quite molluscs, but basically shellfish).
So, the reason I say 'sudden', is because in all likelihood it was nothing like sudden. It's just that it appears sudden because the rock is not preserving all the evidence - it's like a strobe light. You put on a strobe light, and dance. Watch your friends dancing. You only see flashes of what they're doing, not all the bits in between. If one flash of the light they were not wearing a hat, and the next one they were, it'd look to you like the hat just magically appeared. Of course it didn't - they had to pick it up and put it on, but you didn't see that bit.
Um, I hope that explanation helped.
Short version! Short version! :P
Thanks, though. I think I understand random knowledge now.
... anything under a full day's lecture is the short version :P
Glad it helped :D
http://en.wikipedia.org/wiki/Cambrian_explosion
When multicellular organisms suddenly started appearing and diversifying all over the shop.
not a figurative one.
far better than Encyclopaedia Dramatica.
So, do you have those issues with "Tuesday Morning"? Maybe I should become a geologist. I can't remember anything.
I roll out of bed, I go to uni, I look at rocks, I come home, I cook curry, I go to bed, I roll out of bed, I go to uni, I look at rocks ...
Sometimes to liven things up I roll out of bed earlier, I put on my most disgusting clothes, I go to a cliff in the middle of nowhere, I look at rocks, I coat myself liberally in mud by accident, I come home, I cook curry, I go to bed ... :P
Geology is a fine profession for people who can only remember esoteric data, who like heavy lifting, mud, long walks, mud, situations with a high likelihood of personal injury, mud, complicated machinery and mud, and who don't mind things like sleeping for a week on a foam mattress in a half-rotten shack with mouse droppings on every surface :D
... I wish I was exaggerating about the shack with the mousedroppings, but I'm really not.
like you're doing a PhD.
My days were almost all the same. Only way I noticed it was Friday was because most of the senior staff was absent (most of them worked only four days a week).
And yeah, same here. If I can find any of my supervisors/helpful people, it must be Friday ...
And I presume you shower at some point between rolling in and out of bed? Or is the mud bath enough?
Yeah I shower when I'm at home. Not when I'm staying in a shack, cos they don't usually have them.
I took my sister to one of our field stations once. She called it a 'shit little hut'. I was shocked, because after all, this was our swankiest field station; it had both showers AND toilets!
they'd be half rotten and covered with mouse droppings?
And for your sister, it sounds like she likes to live high maintenance? :D
That's probably not 'high maintenance' except by the standards of geologists. But let's face it, when you're surrounded by awesome rocks, who has the time or interest to do something as boring as washing?
or they'll erode.
Also the best place to see stratigraphy is in streambeds :D Where the rocks are wet. And where you get wet also.
Thank Glod for waterproof notebooks, is all I can say!
The science of strations?
Strata being rock layers :)
so far off?
a proofreader. Being a geologist might require interacting. With people. *shudders*
That's my desired career, too!
And it was inspired by joining the PPC, wouldja believe.
Not that I can depend on its income, right now, but I am making money. :)
I was inspired when I stopped being crap at beta reading. I only have a C in English GCSE, but that's because of the freaking Literature side of it. What a load of crap. If they'd split Lit and Lang back up, I'd have aced Lang and happily failed Lit.
I only got Cs in both. But the places around where I live all demand an A-level in English, so now I'm looking at applying to colleges so I can get that. And I'm not doing any freakin' Literature unless I bloody well have to, I hated it.
I'm sick of literature courses. I'm delighted to say I never have to do them again. :)
Seriously, who cares or knows what Shakespeare was thinking when he wrote Random Obscure Line #367982? Unless English teachers have time machines? And if they do, they should put them to better use. Chances are, he thought "hey, this'll be cool."
And that's only if you believe that he didn't plagiarise from others.
.. but you do interact with them a LOT. To the exclusion of almost all other people.
Yes, proofreading might suit you a bit better if you're not a social type.
is a massive understatement. I can't get comfortable with anyone in real life. Pop goes my chance at having children?
Yes, it still requires two people to make a child. While they don't have to be in the same room at the same time to make one, personally I'd say it's probably a bit more entertaining for them if they are ...
... if you can't get comfortable with people, you probably don't really want children, do you? They make noise and mess, after all.
I've always been comfortable with children. Never people of my own age or older. And of people my own age, I've always been more comfortable with women. I never had a "ew, girls are disgusting" stage. I *coughs* vaguely remember even skipping with the girls in lower school (though, in Year Four, I was the only boy in that year, so that may have been simply having nothing better to do).
... as a qualified biologist, that if you get on okay with women and children, that is all the requisite things for breeding. Y'know, women. Getting on with them helps if you wish one to bear your offspring.
and never truly comfortably. My best real life female friend in the last three years was a lesbian. Oh, yeah. I'm good with women.
Well, I'm doomed to spend a loveless existence. Yay?
And please, don't mention the 'w' word. Urgh. Just got asked about a job as an administrator for "Pinnacle Staffing." Meep. Don't want. Don't want! My computer skills tend to revolve around reading the manual and then fixing mistakes by people who didn't. It'll involve people. I'm still waiting for work experience. I just don't want to look ungrateful. Meep!
I hate life. Life sucks. No children in the future, offered jobs which I'm scared of and worse. And yeah, it involved phone contact (which I'm terrified of. I'm no good talking face-to-face, let alone on the phone). Fortunately, I came up with a perfect solution to turn it down. My mum's heavily, heavily disabled and a 9 to 5 job from Mondays to Fridays would stop her ever leaving the house to go to my grandparent's as I'm the only one capable of helping her (i.e. lifting her and her wheelchair up large steps).
Approximately a month ago, on May 6. I'm nineteen now.
...It really doesn't feel that different from eighteen, to be honest.
It was June 11. I'm 24 now. I'm really old. {; )
~Neshomeh, who would have mentioned the birthday, but she was busy playing D&D and spending time with her fiance.