Ancient Skull Challenges Human Origins

Morat · Jul 10, 2002

How deep is the strata where things such as dinosaurs are found? I've heard its not deep and a lot of geological pictures are of men digging on the side of a hill out in bright day light???

Dinosaurs were around a very long time. They're found in many strata. Although none after the KT boundary.

It depends. That strata could be right on top, or buried deep. It all depends on local geologic conditions.

unworthyone · Jul 10, 2002

It really stinks when I can't see what you are talking about.

Like finding a dinoaur bone on the side of a hill is it a few hundred feet deep, 10-50 feet or 1-10 feet, in essence, right on the top layer?

Have they found dinosaurs on all these levels?

Jerry Smith · Jul 10, 2002

How deep is the strata where things such as dinosaurs are found? I've heard its not deep and a lot of geological pictures are of men digging on the side of a hill out in bright day light???

A somewhat hilly or mountainous region could go 100 million years with little or no significant new deposition, and a fair amount of erosion... (chances are there would be some periods of each, though only after the hills had been worn down by erosion - which could take some time).

I have seen some interesting articles about various geological formations where the "surface" age varies significantly in different parts of the formation, but I cannot call them to mind. Being at work now, I will try to look something up for you when I get home.

unworthyone · Jul 10, 2002

Originally posted by Jerry Smith
A somewhat hilly or mountainous region could go 100 million years with little or no significant new deposition, and a fair amount of erosion... (chances are there would be some periods of each, though only after the hills had been worn down by erosion - which could take some time).

I have seen some interesting articles about various geological formations where the "surface" age varies significantly in different parts of the formation, but I cannot call them to mind. Being at work now, I will try to look something up for you when I get home.

Ok cool thanks.

Jerry Smith · Jul 10, 2002

Meantime, maybe this will help:
http://www.surweb.org/surweb/images/cqu/cqu.html

unworthyone · Jul 10, 2002

Originally posted by Jerry Smith
Meantime, maybe this will help:
http://www.surweb.org/surweb/images/cqu/cqu.html

The internal links are broken.

Morat · Jul 10, 2002

The problem most people have with geology is thinking it's all the same.

It's true, in a sense. The rock and land have been shaped by natural processes, that have always acted in the same way.

But people think it's all the same. It's not. In a given layer, you might find deserts, seas, mud-flats and saltpans. You might find it non-existant, having eroded away in the past, or might find it thick and untouched by wind or rain or ice since it's deposition. You might find it buried deep, at the top, or anywhere in between.

It depends on the geologic context of that region. The geological history. Overthrusts, tectonic movements, uplift and erosion. Geology is a complex subject.

Here you can see the geological time scale. The complete geologic column, all those layers, is a pretty rare thing. Generally large portions of them have been eroded away. But it can be found in over 20 places on earth.

Jerry Smith · Jul 10, 2002

The internal links are broken.

Sorry. I'm on the employer's dime right now. Will try to find something better from home tonight. (In between trying to get sense out of our 'friend' and his 'challenge')

unworthyone · Jul 10, 2002

Thanks Morat. Now with the skulls we have now is there anywhere I can see these fossils and where they were found according to the layers?

I don't mean to bug I'd just like to see it.

For instance: this skull was found in this layer, this one was found in this layer.

Do they keep records like that?

Morat · Jul 10, 2002

Sure. The papers describing any fossil finds are quite specific in how and where they were found. Now, whether anyone's collated that information for even the most well-known hominid fossils is another question. I'm guessing "Go dig through the relevant papers" isn't the answer you wanted.

This lists them, and gives the papers they were published in, which would contain that information.

That's probably the best you'll get. They'll all have been found in the Tertiary period of the Cenozoic, heck, in the Neogene even. Hominid fossils are all in the last 10 million years, and the Neogene covers the last 20 to 25 million.

The papers would, as a matter of course, specificy the dating methods.

unworthyone · Jul 10, 2002

Thats not suprising. But considering the mass amounts of information on the net someone should have done this. Maybe I will make this a side-project just for fun.

Morat · Jul 10, 2002

Why? What layer they were in would have only been used for field-analysis. The published dates would have been established by radiometric dating, since you get a much tighter (error-bar wise) date.

Those dates are compiled all over.

unworthyone · Jul 10, 2002

I thought you used the layer to see the estimated age of the fossil.

unworthyone · Jul 10, 2002

We would assume a man buried now would be buried in the holocene layer and then the most recent fossil find in Chad would be in the miocene right?

Or do you date the rocks around the dating method for the fossil?

Or do you date the fossil by the rocks age in geologic column?

Morat · Jul 10, 2002

Yeah. Estimated. Right there in the field. It takes a while to date a rock, you know.

So, if you happen to find a skeleton of a dinosaur in the Triassic period, and you start to brush dirt off the skeleton, you'll know it's between 200 and 250 million years old.

But, if you can date the rock it's in, you'll know it's 235 million years old (plus or minus 3.4 million).

Or, if you can date the rock above and below it, you might narrow it to between 220 and 242 million (including error bars) years old.

Depending on the method, you might get better or worse accuracy.

Using the layers themselves, specifically by identifying the index fossils, is just for getting an idea of "when" you are when working in the field.

When you publish, you use dates established by more accurate means.

So, basically, the geologic column (what layer the fossil is in) is merely a rough guide. The dates assigned in papers are done using more precise methods than that. The difference is sort of like the difference between dead reckoning and GPS.

unworthyone · Jul 10, 2002

So the recent find in Chad would have been found in the Miocene layer and then they would radiometric date the fossil itself to make sure it matches the age of the layer right?

But now I'm confused because you said:

"You don't date fossils directly, but the rock they're laying in. Or between. "

unworthyone · Jul 10, 2002

So are fossils dated by more then just the rocks they sit between? If so, what method is used?

Jerry Smith · Jul 10, 2002

Fossils are estimated by the layer of rocks they are found in. Later, radiometric dating is done on those rocks. If no reliable date can be found by radiometric means for the rocks they are in, then radiometric dating of the rocks above and below them can narrow down the age of the fossil to a certain window, more accurate than the estimation from the layer of rock they are found in, but less accurate than a radiometric date of the rock they are found in... does that help?

Morat · Jul 10, 2002

Let's see if I can explain this.

Bob the Paleontologist is excavating a hillside. He knows he's in the Triassic period, based on the strata he's excavated. Depending on how finely geologists can detail strata (something I don't know, but could find out) he might be able to tell within 5 to 10 million years or better "when" he is.

He finds a dinosaur fossil embedded in rock. He knows, because of the layer he's in, a rough age. He excavates the thing and has it shipped to his lab for study. He notes that the fossil is lying in a certain type of rock, one that is easy to date by the Ar/Ar method.

He ships this rock to another lab, thankful his grant covers the more expensive Ar/Ar method. (He probably sends more than one, actually).

Bob proceeds to clean his dinosaur fossil, discovers to his delight that several features indicate it is a new species. During this laborous process, he gets the results back from the radiometric dating done on his sample. The rock is dated at 234 million years, plus or minus 1.2 million. He claps his hands in delight, as this date is much more precise than the 230 to 240 million year figure given by it's position in the rock.

He then writes a paper, detailing the skeleton, the specific features of it, and his conclusions. In that paper he details the specifics of the find. Geologic location, position in strata, how deep it was buried, what sort of rock it was in, the geologic history of the area, and how many samples he had submitted to how many tests. Where the samples where taken, relative to the fossil, and what the results where from the radiometric tests.

Multiple methods. He knew, from the layer it was in (a layer he identified by index fossils) a rough age of the find. He refined that age (and independently tested his identification of the layer) by submitting rock samples from the find to radiometric tests.

unworthyone · Jul 10, 2002

Okay i think understand now and thanks guys for telling me that.

Now how did they come to the conclusion that that dating method was correct for that layer and that rock? What reference was used?

I'm asking because you are describing in laymans terms and I'm understanding it somewhat....nobody ever wants to do that.

Ancient Skull Challenges Human Origins

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