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gieserguy

How can you determine time scale of fossils?

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gieserguy

Since joining this group, I've realized the importance of knowing what time period your fossils are coming from, but how do you do that? For example, say I'm out collecting at a road cut, how would I know when the fossils are from?

 

I apologize if this seems like a dumb question. 

 

 

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Mark Kmiecik

First of all, there is no such thing as a dumb question!

 

The answer is it's easy. All you have to do is look at the maps and charts that people made for us a hundred years ago or more. Click on this http://isgs.illinois.edu/maps/isgs-quads/cobden-geology?quad=All&program=All&theme=Surficial+Geology+and+Features and explore. Start with quadrangle maps and take it from there. Google gelogical time scale.

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Macrophyseter
6 hours ago, gieserguy said:

I apologize if this seems like a dumb question. 

There are no dumb questions. Otherwise no scientist would ever do science. ;)

 

Usually, the age of a fossil is based on the age of the rock formation it has been found in. You can research rock formations you will hunt in and their determined ages (You can search up geological records of the area or alternativeky go to popular hunting sites that are better documented). For example, I find a shark tooth from Calvert Cliffs in Maryland. I know the area in the cliffs I found the shark tooth from is part of the Calvert Formation, which is dated Middle Miocene. Therefore, the shark tooth is dated to be from the Middle Miocene.

 

 

If you want to go farther than that and know the specific age of a specific layer the fossil was from (As in specific Ma), we usually look for certain specific fossil species in the same layer known as index fossils (usually represented as extremely common invertebrates like trilobites during the Paleozoic, ammonites in Mesozoic, and clams in Cenozoic for example). Then you can look up the exact datings of these contemporaneus index fossils. For example, I find an index clam fossil in the exact same layer from the shark tooth I found. That clam species has been dated 16.44 Ma, therefore the shark tooth is likely dated 16.44 million years old.

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gieserguy

@Macrophyseter Thank you so much! That's really helpful.

For the geological records, would a quick google search show what I'm looking for?

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gieserguy

@Mark Kmiecik Somehow I didn't see your comment! Thank you!!!

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Macrophyseter
2 minutes ago, gieserguy said:

@Macrophyseter Thank you so much! That's really helpful.

For the geological records, would a quick google search show what I'm looking for?

When it comes to well-known formations like Mazon Creek, a quick google search can do. As far as I know, most geological records are also avaliable online as many of them are technically government documents and are legally obligated to be so.

 

If you want to go with index fossils, it could be a bit harder. The best one I know of, Gradstein et al. (2012), is a scientific book that's locked up at unscrupulously exorbitant prices by Elsevier.

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Mark Kmiecik
1 minute ago, gieserguy said:

@Mark Kmiecik Somehow I didn't see your comment! Thank you!!!

When you Google "geological time scale" and look at the major divisions, you'll see that many of them are broken down into smaller ones, and many of those are broken down into even smaller ones and so on until you get to that 6meter, 6foot or 6inch layer of gray clay or bituminous coal you found in the wall of the creek bank. Some are found everywhere around the globe, some are local, most are at least interrupted in most locations. It gets complicated by what got pushed, eroded, folded, etc., but all the work of figuring that out has already been done. All you have to do is look it up.

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Mark Kmiecik
Just now, Macrophyseter said:

@Fossildude19 I'm experiencing a glitch in the text box in my first post where a line of "Kmiecik" gets automatically added everytime I try to delete it, and it autoposts the glitched version everytime I try to delete the whole thing altogether. Do you know any sort of fixes for this?

Did  you try clicking the X at the bottom right of the dialogue box?

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gieserguy
15 minutes ago, Macrophyseter said:

If you want to go with index fossils, it could be a bit harder. The best one I know of, Gradstein et al. (2012), is a scientific book that's locked up at unscrupulously exorbitant prices by Elsevier.

I think you might be happy to hear that I just downloaded a copy because my university gives us access to countless scientific resources!

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Macrophyseter
26 minutes ago, gieserguy said:

I think you might be happy to hear that I just downloaded a copy because my university gives us access to countless scientific resources!

Thanks for the offer, but I already have access to the book. ;)

 

Also, I am genuinely suprisied that your university retains access to such resources, considering how Elsevier has been unscrupulously raising the prices so high that even Harvard complains that it can't afford them.

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Mark Kmiecik

There's some geological time scale "wall charts" available for less than $20 that are worth having as a quick reference and some also show index fossils for each sedimentary stratum.

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connorp

This is one thing I will thank mining companies for. They poured tons of money into meticulously mapping and dating most available surface rock, you just have to search a bit to find the records.

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DPS Ammonite

The gold standard and nearly globally accepted geological time chart is from the ICS. We use it as our guide in the Collections section of the Forum. 

 

ChronostratChart2018-08.pdf

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gieserguy

Another question to add to this thread - How would you determine the time scale of a single fossil? For example, if you just have a coral that was present in the Ordovician, Silurian, and Devonian periods.

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DPS Ammonite
2 minutes ago, gieserguy said:

Another question to add to this thread - How would you determine the time scale of a single fossil? For example, if you just have a coral that was present in the Ordovician, Silurian, and Devonian periods.

If you had no other fossils, either look at a geological map to see the ages of the rock layers based on locality and/or try to figure out the name of the rock layers based on their physical properties such as composition, color, bedding etc. using geological papers about the local rock units.

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erose

As you start studying maps and other more technical publications to determine the formation and age of a specimen you will also start to see that there are different terms for chronology and stratigraphy/lithology. For example ages versus stages. And there are also european terms used in some papers and North American terms in others.  That is where correlation charts come in handy.

 

Also you may find discrepencies between maps or papers. Some rock units will be better dated than others. It will depend on how much attention professional geologists spent on it as well as how recent the study was. Areas with lots of economic geology get more attention.  

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Mark Kmiecik
23 hours ago, gieserguy said:

Another question to add to this thread - How would you determine the time scale of a single fossil? For example, if you just have a coral that was present in the Ordovician, Silurian, and Devonian periods.

That's where the fun starts and you become a fossil detective. Not everything is known at this point, and anything you, as an amateur or professional, can add to our collective knowledge will be appreciated for all time. All it takes is logic, time and enough of the same or similar specimens to formulate hypotheses and have them proven or disproven by either you or others. And a disproven hypothesis is no less important than one proven true in that it leads us one step closer to the truth.

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Kane
11 minutes ago, Mark Kmiecik said:

All it takes is logic, time and enough of the same or similar specimens to formulate hypotheses and have them proven or disproven by either you or others. And a disproven hypothesis is no less important than one proven true in that it leads us one step closer to the truth.

https://www.nsta.org/publications/news/story.aspx?id=52402

https://staff.washington.edu/lynnhank/Popper-1.pdf

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Mark Kmiecik
5 minutes ago, Kane said:

A hypothesis that is not disproven eventually becomes a theory. A theory is the best explanation we have up to this point in time. It may eventually be disproven and at that point a new hypothesis is formed. And so on . . . . 

 

And yet, in the common vernacular the dictionary definition is ignored in favor of popular opinion. Perhaps we need better schooling.

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Kane
1 minute ago, Mark Kmiecik said:

A hypothesis that is not disproven eventually becomes a theory. A theory is the best explanation we have up to this point in time. It may eventually be disproven and at that point a new hypothesis is formed. And so on . . . . 

You mentioned hypotheses being proven, which does not actually happen in science. Proof occurs in mathematics and logic. 

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Mark Kmiecik
2 minutes ago, Kane said:

You mentioned hypotheses being proven, which does not actually happen in science. Proof occurs in mathematics and logic. 

I stand corrected. I should have said "stands the course of time" instead of proven. Nevertheless, I think everyone got the point, regardless of semantics.

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Kane
14 minutes ago, Mark Kmiecik said:

I stand corrected. I should have said "stands the course of time" instead of proven. Nevertheless, I think everyone got the point, regardless of semantics.

Not just semantics. Precision in language -- and particularly with respect to science -- is vitally important. 

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