Talk:Geologic time scale

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Peer review This article was externally reviewed on July 1, 2005 by The Roanoke Times. Geologist Bob Bodnar of Virginia Tech found "the terminology and ages used [in the article] to be quite accurate and consistent with the most recent data." See the Wikipedia Signpost article.
Peer review Geologic time scale has had a peer review by Wikipedia editors which is now archived. It may contain ideas you can use to improve this article.

I'm pretty sure that there is an article on Radiometric dating under some name variant or other, but I can't seem to locate it. For the time being, I'll write another and I (or, better, somebody who actually knows about the subject) can clean the multiple articles up.

You probably mean the Radiocarbon dating page. There probably should be a broader page that also deals with dating using other radio-isotopes. --Eob. I thought there was a more general article as well -- no matter djk.

Is there a specific reason why this is an ASCII table instead of a HTML one?

Because that's the way whoever put it in formatted it. I left it that way when I worked it over because I'm a firm believer that the simplest approach to most things that works fairly well is usually the best one. --djk

Contents

[edit] Appearance of Flowering Plants

Angiosperms first appeared in the Jurassic, not the Cretaceous. I have slightly altered the mention of them in the column so that it says they "proliferate"d in the Cretaceous, not they "appear"ed. Ventifact 05:01, 15 May 2006 (UTC)Ventifact

[edit] Age versus Stage

I noticed that throughout many articles in Wikipedia, the smallest subdivision of geologic time is referred to as a Stage. While I have used the same nomenclature in my own articles in order to be consistent with the project, I wanted to bring up the fact that this is technically not correct. Stage is a stratigraphic term referring to a bed of rock that corresponds to what in the geologic time scale is referred to as an Age. An Age is the "geochronologic" equivalent of a Stage. Thus, an age is the proper term for the smallest division of geologic time. Though, you can have sub-ages if necessary.

I am basing this on The International Stratigraphic Guide, Second Edition, 1994, The Geological Society of America and The International Union of Geological Sciences. Age is defined on page 106, and Stage is defined on page 136. Also, section 9.C.2 and Table 3 (pages 78 and 79) deal with the stratigraphic and time scale subdivisions and how they relate to one another.

I would like to get other people's input. I believe that all occurrences of Stage in Wikipedia that refer to time scale should be changed to Age. What do other people think?

Likewise, "Late" and "upper", and "early" and "lower" are not interchangeable - Late and Early are time terms, Upper and Lower refer to rocks. You should not talk about "Late Cretaceous chalk" for example, nor about "upper Cretaceous events". Generally, in this article about geologic time, "upper" and "lower" have no place, except in terms of explaning the difference between them and the time terms. --Geologyguy 15:12, 9 April 2006 (UTC)

Actually, you can talk about "late Cretaceous chalk." It's chalk that was deposited during the late Cretaceous. Rocks can be described by upper/lower or by late/early.
You can, and many do. But it is not correct. "Early" and "late" are time terms. From the Glossary of Geology: early "applied to the name of a geologic time unit (era, period, epoch) to indicate relative time designation, and corresponds to lower as applied to the name of the equivalent time-stratigraphic unit; e.g. rocks of a Lower Jurassic batholith were intruded in Early Jurassic time." So, strictly speaking, chalk that was deposited during the Late Cretaceous must be Upper Cretaceous chalk. You could talk about Upper Cretaceous chalk and everyone would know it was deposited in Late Cretaceous time. Or you could talk about chalk of Late Cretaceous age and everyone would know it was from the upper part of the Cretaceous System (system is the rock equivalent of period, the time term). I know it is nit-picky, but this is the correct formal usage, according to the Glossary of Geology as well as the USGS Suggestions to Authors. Also, the adjectives - early, middle, late, lower, middle, upper, are capitalized when the division is formal, as with Upper and Lower (or Late and Early) Cretaceous, but upper Paleozoic and early Eocene. There is a good discussion here: [1]. --Geologyguy 22:03, 15 May 2006 (UTC)

[edit] Palaeozoic / Paleozoic

I'm noticing that the page for the era is Palaeozoic though most of the links trying to reach that page are spelled "Paleozoic". Is one more correct than the other? -- RjLesch.

As far as I can tell, both spellings are acceptable. Without the extra a is more common -- especially in American English -- but the original link was set up with the other spelling. Same story on Paleogene

Yes, Palaeozoic, Palaeogene, and Palaeontology are all UK spellings, while Paleozoic, Paleogene, and Paleontology are U.S. spellings. But, which should be used here? --Lenn 17:56, Jun 23, 2005 (UTC)


Wikipedia already has guidelines set up to answer that question.

[edit] First Fish

6/15/02 I removed "first fish" from the Ordovician because in the past five years, a number of (probable) chordates have turned up in the Lower Cambrian of China. Two of them are almost certainly "fish". No intent to start a war. If anyone wants the first fish back in the Ordovician, put them back and I promise to leave them alone. djk

[edit] HTML table

Note that the improvement that converted the table to HTML moved the date of the end of the period to line up with the name and description whereas with the "primitive" ascii, it was (as it should be) lined up with the line delineating the end of one period and the start of the next. If anyone can think of any easy way to put the dates back where they belong, please do so. (... yet more proof tht Ned Ludd and his followers had a point).

[edit] Neophyte question

I'm a neophyte just trying to learn the Geologic Time Scale for the first time (however noticed all the different presentations),and so comment (question, actually)with trepidation. I don't understand what is being said in 5) near the end of the article: "In common usage the Tertiary-Quaternary and Paleogene-Neogene-Quaternary Periods are treated as equivalents to the Mesozoic and Paleozoic Periods". Are you saying in part that the Mesozoic and Paleozoic Ages are, in common usage, sometimes regarded/referred to as Periods? I'm also not sure what you mean by "treated as equivalents"; strictly on word-meaning, I would take this to mean that the Tertiary-Quaternary covers the same time period as the Mesozoic, and the Paleogene-Neogene-Quaternary as the Paleozoic, but its obvious from the Time Scale you don't mean that. I think probably it's meant that these are placed on the same level (in this case, figuratively in the same column) or given the same weight, etc. I would really appreciate some clarification on this, because its the presentation of the origin, variation, and use of the Geologic Time Scale terms here and in other related articles, that I find so valuable.


Is the Proterozoic subdivision verified? This page says that it includes

  • Hadean
  • Archean
  • Paleoproterozoic
  • Mesoproterozoic
  • Neoproterozoic

However other sources list

  • Hadean
  • Archean
  • Proterozoic
    • Paleoproterozoic
    • Mesoproterozoic
    • Neoproterozoic

Help, anyone? - fagan

Why are the epochs in the cretaceous and before not shown? should be added. I tried to do so, but I can't get the table formatting to work. Can someone else do this? Amblypygi 16:37, 17 Apr 2004 (UTC)

The Ediacaran has been upgraded to a bonafide geologic period. http://news.bbc.co.uk/2/hi/science/nature/3721481.stm Therefore, it will have to be squeezed in between the Cambrian and Neoproterozoic.TimothyPilgrim 15:35, May 20, 2004 (UTC)

Actually the Neoproterozoic should be an Era (not a period) and one which contains the Ediacaran period. Likewise, Proterozoic, Archean and Hadean are technically eons, not eras. Essentially the whole botton part of that chart needs to be shifted. I suggest refering to the Geowhen database or the ICS list (both linked at the bottom of the article) to see how it ought to be set up. Dragons flight 17:12, May 21, 2004 (UTC)


[edit] Boundaries

(William M. Connolley 19:11, 22 Sep 2004 (UTC)) I notice that the period boundaries aren't defined in the table. To me this seems odd. For example, the pleistocene/holocene boundary is the end of the last ice age, which is important. Could this be incoporrated into the table?

Technically the Pleistocene/Holocene boundary is 10000 Carbon-14 years BP, and I'm not sure many of the other boundaries are particularly informative either. The end of the Cretaceous, Jurassic, Triassic, Permian, Ordovician, and Silurian are all exinction events. The Devonian boundary is slightly after a major extinction. The end of the Cambrian is the onset of an adaptive radiation, and the ends of the Carboniferous and Paleogene are basically arbitrary.
One probably could list all of the extinctions, but I'm not sure that is all that useful or at all that easy to incorporate. I did however add end of ice age to the events of the Holocene.
Dragons flight 06:25, Sep 23, 2004 (UTC)

[edit] Note 5

I have a degree in geology, and I'm not sure what note 5 is getting at. Is it suggesting that "Tertiary" (or "Neogene and Paleogene") and "Quaternary" are sometimes regarded as being at the same level as "Mesozoic" and "Paleozoic"? If someone can't explain this, we should probably remove that note. Gwimpey 20:59, Nov 16, 2004 (UTC)

Since some time the term "Tertiary" is out of use and there are two periods which replace the Tertiary: "Neogene and Paleogene". Perhaps the note should point in that direction. Surely they are not in the same level as "Mesozoic". --chd 10:05, 19 Nov 2004 (UTC)

[edit] Mnemonic for the Geological Timescale

When I first started studying geology, I found it difficult to remember the order of the periods. The following mnemonic [for the Cambrian to Holocene] helped. It is modified from one passed down through the generations of students at my college, so I'm afraid I can't acknowledge the original source: Camels Ordinarily Sit Down Carefully, Perhaps Their Joints Creak [Probably Even Old Mules Plod Peacefully Home]

[edit] Discussion item - nav boxes

Cross posting for those who might not otherwise notice, to point out the discussion item I added at Wikipedia_talk:WikiProject_Geologic_Timescale#Top_navigational_templates. —Mike 09:19, Jan 27, 2005 (UTC)

[edit] Periods?

I am working on sr: timeline scales and calendars. It seems that this page was changed: where are Tertiary and Quaternary? As I am not geologist (or paleologist or...), I am confused. What is Quaternary and what is Neogene? --Millosh 08:40, 20 Feb 2005 (UTC)

Effective with the 2004 time scale, the International Commission on Stratigraphy has removed "Tertiary" and "Quaternary" from the set of stratigraphic terms recommended for formal usage. Instead the usage of "Neogene" and "Paleogene" Periods, as shown on the page, is reccomended.
Dragons flight 09:08, Feb 20, 2005 (UTC)
Thanks for quick response. I'll remove Tertiary and Quaternary from sr:, too. (I mean from timeline scales.) --Millosh 10:23, 20 Feb 2005 (UTC)

[edit] JCHYSK's Hadean

JCHYSK recently added 4 subdivisions to the Hadean. I am inclined to revert this on two grounds a) they are not part of the formal ICS nomenclature (even though they are admittedly well established), and b) I just think having a compressed Hadean looked better. It is not like very many people are going to come along and care about the divisions of the Hadean. This is basically the same reason for not using all the upper and lower epochs of the Mesozoic and Paleozoic, it just gets messy, and links on this page can provide additional detail for those that actually need it.

Anyway, that's my feelings on the matter, but before I reverted it, I thought it is worth posting here for comment. Dragons flight 13:05, Mar 4, 2005 (UTC)

As for me, I would prefer to actually have Cryptic, Basin Groups, Nectarian and Lower Imbrian on the chart. As for the appearance, a border (or better yet, an outline, CSS-speaking) could fill the bill of not cluttering the chart:
  • different consideration (official/not official)
  • different styling (background color/border color)

Reply to David Latapie 00:35, 22 May 2006 (UTC)

[edit] Removal of Hadean from main chart

The chart dosn't include Precambrian, Tertiary and Quaternary. These divisions, like Hadean, are not official ICS nomenclature, but are (still) in widespread use with some Geologists. Addind these divisions would seriously clutter the chart and I think everyone would agree that it would be a mistake. By that logic, Hadean should be removed. The inclusion of Hadean is confusing: The way the current chart stands, a naive reader would believe that the Archaean and Eoarchean begin 3800 mya, whereas actually they have no lower boundary according to the ICS. Also, it seems sort of silly to have an entire chart except one entry fit with ICS nomenclature. I think that Hadean should be reslihed to being a footnote. Comments? -Casito⇝Talk 19:54, 25 Apr 2005 (UTC)

I am opposed to this. I don't think the Hadean contributes to clutter the way the other cited terms would. You are correct that it not currently part of the formal nomenclature, but it is pretty much the de facto term for the earliest part of Earth's history. Potentially more important, the Precambrian Subcommission of the ICS is calling for its ratification as formal division, with voting on this issue to start later this year. The biggest hold up has been that people are having a hard time defining where the beginning of the Archean ought to be. Some prefer using a 3800 Ma GSSA (or some similar time), but others want to define a GSSP associated with the earliest known crustal rocks. So while they argue about this, the base of the Archean is left hanging, though I don't know of anyone who actually wants the Archean to extend all the way back to the formation of Earth. So basically, I think it makes sense to leave the Hadean in, following common usage, while we wait for the ICS to get their act together and decide how exactly they want to define the earliest part of Earth's history, which will probably mean including a Hadean anyway. Dragons flight 20:27, Apr 25, 2005 (UTC)
Okay. Let's leave it in. Once ICS makes up their mind, we should be sure to update the chart, and change its color once the USGS adopts one. Thanks. -Casito⇝Talk 20:33, 25 Apr 2005 (UTC)

[edit] USGS

How can it be said that the USGS doesn't recognize the Hadean when it is a term both in their Thesaurus and a search term in GEOLEX? --Bejnar 03:39, 17 January 2007 (UTC)

[edit] Carboniferous

Apart from the Gzelian and Kasimovian (in the Late Pensylvanian), the Early Middle and Late divisions of the Mississipian and Pensylvanian match exactly with the well-known epoch names of Tournaisian, Visean, etc. For this reason, I feel that this should be allowed to stand, rather than reverting back to the earlier version. Ok i know that Gradstein and Ogg 2004 use Early Middle and Late for each of the Carbooniferous subperiods, but this seems completely redudant, and the Carboniferous epoch names are well established. M Alan Kazlev 09:18, 8 May 2005 (UTC)

We say in the header that the timescale follows ICS conventions, and I think it is problematic to start deviating from that, since there are any number of places where one could. (The single exception to ICS conventions at present is the Hadean which is footnoted and follows the discussion given above (i.e. noting that the Hadean is a sort of preconvention convention)) Also, while I agree that the names are well-established, I would question whether they are well-established as "epochs". Harland 1989 used them that way, but both the GSA and ICS have prepared time scales where they are listed as stages, not epochs. I agree with you that it is somewhat awkwardly redundant, but that strikes me as the ICS's problem. In my opinion, consistency is more important than trying to overcome what may be viewed as the failings of the ICS nomenclature. Dragons flight 16:44, May 8, 2005 (UTC)

[edit] Continents vs. Critters

It would make sense to separate columns on the table for geology and biology. Show what was going on with the various continents and supercontinents - Rodinia .. Pannotia .. Pangea .. etc in one column with biological evolution over to the right. It is difficult to read as it is. Quinobi 08:49, 8 Jun 2005 (UTC)

But what about climate etc? Or we could have geology, climate etc in one column, and the evolution of life in the other. But would there be enough space available, considering how crowded the table is already? M Alan Kazlev 04:02, 29 September 2005 (UTC)

[edit] Congratulations

This page is "quite accurate" and "consistent with the most recent data".

Wikipedia:Wikipedia_Signpost/2005-07-04/In_the_news

Dragons flight 16:14, July 11, 2005 (UTC)

[edit] Table of geologic time - recent series/epochs

I like the way the table of geologic time shows the calculated error values for the column giving the start times, but is there any way to change from "millions of years ago" for the earlier times, to thousands of years for the Holocene Epoch; and maybe also from milions to billions for the earliest times (unless many people still use the outdated milion million for a billion)? ie. The Holocene started 11,430 years ago, +/- 130 years? Since it is only one entry that might confuse people with a start date of 0.011430 million years ago, maybe leave it that way in the table, and add a footnote giving this value in thousands of years? 194.200.237.219 11:21, 17 October 2005 (UTC)

[edit] Table footnotes

I understand that the footnote system is largely used for linking passages to their relevant references, but is there any reason it should not be used for the numbered footnotes within the Table of geologic time? Lusanaherandraton 06:45, 18 November 2005 (UTC)

[edit] Great work!

BBC links to you from their Prehistoric life site. Congratulations! — Knowledge Seeker দ 05:34, 7 April 2006 (UTC)


[edit] Early/Late vs Lower/Upper

I added an explanation in the Terminology section differentiating between these words' uses. Reference, Glossary of Geology: "lower - pertaining to rocks or strata that are normally below those of later formations of the same subdivision of rocks. The adjective is applied to the name of a time-stratigraphic unit (system, series, stage - see also comment by someone near the top of this page - system, series, and stage are rock equivalents of the time terms period, epoch, and age, respectively) to indicate position in the geologic column and corresponds to early as applied to the name of the equivalent geologic-time unit; e.g. rocks of the Lower Jurassic System were formed during the Early Jurassic Period. The initial letter of the term is capitalized to indicate a formal subdivision and is lowercased to indicate an informal subdivision." I can't find the most recent edition of the USGS Suggestions to Authors, but I'm sure this usage is followed there too, and my copy of the International Commission on Stratigraphy time scale does not use the words Lower or Upper anywhere, but I'd leave them on the graphical column on this page because many time scales do include both. I've made appropriate changes on some of the pages for periods and stages (most of Mesozoic, working on Paleozoic). --Geologyguy 14:36, 30 April 2006 (UTC)

[edit] Radiometric Dating = a measurement tool, NOT a piece of evidence.

Was: ...Current radiometric dating evidence indicates an age of the Earth of about 4570 million years old...

Should Be: ...Current radiometric dating indicates an...

All measurements are made by methods, tools and standards. All methods, tools and standards are characterized by uncertainties and assumptions. It is merely a measurement, not necessarily a piece of evidence, especially not in the interpretive context here. In fact, it is a measurement, further "post-processed" via mathematical models. The end result is a rough calculation. A calculated result may be evidence of a method, but the method is not evidence of its calculated result.

Presence of carbon left somewhere, for example, can be a piece of evidence. A measured amount is not evidence, it is a measurement, already subject to the weaknesses of uncertainties and assumptions. The interpretation of said measurement, via post-processing or other is even less a piece of evidence. That many such intepretations agree is also not evidence. It is massaged data.

For instance, in the fields of mechanical engineering, there is the ASTM (American Society for Testing and Materials). These are field established means to get all communications on the same page.

Perhaps this discussion of what is acceptably coined "evidence" is a philosophical discussion in itself.

In my PhD work in failure of continuum mechanics medium at Purdue University, the overriding philosophy was that if you do not understand the underlying assumptions in your models, you are not ready to present. If you do, you will be overwhelmed with humility at the real obsurdity with what we deal. In other words, if you do not understand the assumptions, forget about defending a thesis. Your candidacy should never have occurred.

Hopefully, Wikipedia can adhere to high standards of academic integrity such as this and not be just another stream of journalistic (ie drop-out from the pure or applied sciences) garbage where loaded words are carelessly applied.

(Above unsigned five edits by anon. 192.35.35.34)
No. Radiometric dating is not a tool, it is a technique or batch of different techniques that use a variety of physical tools (scintillation counters, mass spectrometers ... etc) to gather the raw data which is the evidence. Your piece of carbon left somewhere is not in itself evidence. The evidence are the data which we derive from that piece of carbon with our scientific techniques and tools. The measurements (data) made with the tools using the techniques of radiometric dating are the evidence.
An analogy would be the our understanding of the composition of stellar atmospheres. We gather light from the star and using the tools of spectrography we gather the data that is the evidence for our understanding of the star atmosphere.
For a different analogy. A geologist uses a tool, the Brunton compass, to measure the attitude of strata in a complex area. the dip and strike data are ploted and analysed to decipher the structure of the region. The dip and strike measurements are the evidence supporting the interpreted structure.
The tool or technique used is not the evidence. The evidence is the data aquired or measured with the tools.
The data gathered by the tools of the radiometric dating techniques are the evidence for the ages of rocks. A single piece of data (datum point) doesn't suffice, it must be backed up by other data collected by the study.
Radiometric dating techniques and the tools they utilise have been in use for nearly a century and have been (and continue to be) fine tuned and refined to make sure the data collected is adequate to use as the evidence in a variety of academic and commercial applications.
Now, your bragging about your PhD is irrelevant here, in fact it simply brings to mind the old saw: Phd = piled higher and deeper. And if you don't know what is piled, then you must be out of the loop. Cheers, Vsmith 23:17, 15 May 2006 (UTC)

Yes. The PhD itself is irrelevant (as are the qualifications of anybody who's contributed anything to any field); and neither is it bragging. Hopefully, you are not implying that the philosophy of high academic integrity is irrelevant. Though these techniques and tools (and we would add the largepart of the collection of datapoints) have been in use for nearly a century and fine tuned, their basic assumptions remain common and the same. If the assumptions are found at a loss, the entire deck of cards collapses; and the game is over. That is what a PhD means that one should understand. Others usually don't. And if you don't know what the danger is with assumptions are, then being in the loop is the least of your concerns. Regards, User:192.35.35.34, 17 May 2006 (UTC)

So, if you are aware of some basic flaw in the assumptions that radiometric dating is based on, then I'd suggest discussing it on the talk page of that article and not here. Now, if the conflict is simply between the assumptions behind the science and the assumptions that your religious views are based on -- discussion over. Cheers, Vsmith 01:56, 18 May 2006 (UTC)

Toot toot! I find the reasons behind the one-word change to this article filled with rhetoric. If I measure PhD Pat's editing using current "methods" and "standards," the most accurate terminology would be "recent radiometric dating" or "prevalent radiometric dating," rather than his "corrected" "current radiometric dating." The term "current" assumes immediately present technique and technology, which is incorrect.

[edit] merge fossils article in?

there is a shorter article called Fossils and the geological timescale, it should probably be merged in with this better more complete article, but i'm not sure how to do it.

Made that a simple redirect here as the info there was rather sketchy and much more is already here. Vsmith 03:01, 24 May 2006 (UTC)

[edit] Inaccuracy of statement "no way to determine time scale represented"

While they didn't have a good way to determine the time scale represented, it is incorrect to say they had no way at all. In fact, early geologists had good information by which they knew that the time scales was in hundreds of millions of years even though they could not be very precise about anything. Greeneto 16:33, 2 June 2006 (UTC)

Timothy Clemans has stated arbitrarily that my point here is incorrect, but without any explanation whatsoever. My statement is correct, and I was hoping for someone more knowledgeable to address the specific issue (which Timothy unfortunately just ignored) and reword the sentence correctly. Since now even the fact that the sentence itself is incorrect (which is what the tag was for the purpose of flagging) is being removed, looks like I'll reword the sentence in a vague manner myself. I hope someone will come along soon who can give it a little more detailed explanation. (Greeneto 01:03, 11 June 2006 (UTC))

Hello - what exactly is the sentence needing rewording? As near as I can tell the changes Greeneto made look good; indeed, the early geologists did have ways to determine absolute age, but (as you say) they were not very accurate. It seems to me that this history part of the article should focus most on the relative time scale, which was what the British geols developed well; the references to absolute age are appropriate but discussion in depth could go in the article Age of the Earth. Just my 2 cents --Geologyguy 01:35, 11 June 2006 (UTC)

[edit] History of the time scale

I created a comparison of Lyell's 1833 scale with the modern scale here. I arbitrarily cut it off 650 mya, since Lyell didn't demarcate boundaries past what is today the Phanerozoic, but I think it makes for an interesting visual comparison. Anyone object to my adding the timelines to "History of the time scale"? Or any suggestions for improvement? -- bcasterline • talk 04:41, 26 June 2006 (UTC)

[edit] Holocene timescale

One of the footnotes needs more context and corrections:

  • "The start time for the Holocene epoch is here given as 11,430 years ago ± 130 years (that is, between 9560 B.C. and 9300 B.C.). For further discussion of the dating of this epoch, see Holocene."

Firstly, as this is the time period closest to today's time, when people calculate what "11,430 years ago" means, they need to know when this calculation was made? 1950? 1970? 2004? Does anyone know? Ah. Looking at footnote 2, I see these values are based on the International Commission on Stratigraphy 2004 time scale - so 2004 was a good guess on my part! :-)

Secondly, calculating "9560 B.C. and 9300 B.C." from "11,430 years ago ± 130 years" from 2004, seems wrong. Shouldn't it be 9426 BC ± 130 years? That is 9556 B.C. to 9296 B.C. as the range. The range quoted in the article assumes the dating was done in the year 2000. What is going on here? Was the original table based on the International Commission on Stratigraphy 2000 time scale (if such a thing exists)? Carcharoth 00:40, 2 July 2006 (UTC)

Geological convention is that "years ago" and "years before present" are with respect to 1950. Hence 11,430 years ago should be 9,480 BC. Also, one shouldn't carry more than one digits than make sense with the error estimate. Hence 151,123 +/- 1200 should always be reported as 151,100, etc. In this case the correct numbers are 9610 BC to 9350 BC. Dragons flight 00:53, 2 July 2006 (UTC)
Ah. 1950 is the convention. Thanks. I never knew that. Has all this been added to the article? Carcharoth
PS. After puzzling over your 'error estimate' bit, I think I see where we've misunderstood each other. When I said 9426 BC ± 130, I was presenting a number generated from a calculation. ie. 2004 A.D. - (11,430 ± 130) = 9426 BC ± 130. I didn't mean to imply that the error of ± 130 was in the figure of 9426 BC, which is what I think prompted your bit about error estimates. I was merely placing the error bar around a point in time 11,430 years before 2004 AD. Hope that clears up any misunderstanding. Carcharoth 01:25, 2 July 2006 (UTC)
Hmm. Investigating further, I found an HTML version of a PDF document from the International Commission on Stratigraphy. That document gives the Holocene boundary as "0.0118 Mya", which differs by four from the "0.0114" figure above, which makes sense if that document was published in 2004, but our figure refers to a document published in 2000 (it would account for the 4-year time difference). So it seems our figures are internally consistent, but the discrepancy with the latest charts need to be corrected or explained. Either we need to increase this figure by one every year, like the ICS seem to do, or we need to make clear when the definition/measurement was publiched/made. Carcharoth 00:51, 2 July 2006 (UTC)
0.0118 Mya would be 11,800 years ago, a difference of 400 years not 4 years. Dragons flight 00:53, 2 July 2006 (UTC)
OOPS!! :-) You are quite right. I must avoid doing mental calculations late at night... I assume that the article needs updating if this is indeed a new figure used by the ICS? Carcharoth 01:02, 2 July 2006 (UTC)

I've checked again, and the ICS chart definitely says "0.0118" instead of "0.0114". I also found the chart at this link, which should be authoritative enough. I think the value for Holocene needs updating here and at Holocene. I'm also uncertain as to where the error values for the more recent epochs are coming from. They aren't on any of the charts I've been able to access online. Carcharoth 01:19, 2 July 2006 (UTC)

It comes from the definition of the Holocene as starting exactly 10000 radiocarbon years before present. Assuming your reference is authoritative, it would appear that this informal definition has been supplanted by one referencing the Younger Dryas event. Dragons flight 01:55, 2 July 2006 (UTC)
The authors of A Geologic Time Scale 2004 suggest that the ICS is trying to move away from dating chronometrically even in the Precambrian, so it makes sense that they would avoid a chronometric definition for the base of the Holocene and rely on a climatic event instead. -- bcasterline • talk 03:03, 2 July 2006 (UTC)
I also wonder about the Neogene error values. The footnote says the values come from the 2004 ICS scale, but that stratigraphy.org chart is a recreation of the published chart, and both provide ± 0.00. -- bcasterline • talk 03:03, 2 July 2006 (UTC)

Well, as long as you two can sort something out, that would be great. I don't know enough about this sort of thing, but I do like to point out stuff like this when I spot it. The Neogene error values almost certainly come from an earlier edit that wasn't referenced. It may require someone to dig back through the page history to find out, or just quietly replace it with the latest, most up-to-date information, unless someone wants to start an article tracing the evolution of the international data and definitions of the geologic timescales and how the values varied over time until the final values were settled! Carcharoth 12:55, 2 July 2006 (UTC)

[edit] What does the * mean in the table?

I'm noticing that in the table of timeperiods, the number in the "start" column has a superscripted * in almost every row down to Ediacaran. I'd normally expect that to mean there's a footnote for those, but I can't find any footnote marked with a star so I have no idea what it means. Also, while I'm on the subject, the start date for the Ediacaran is messed up; it reads "630 +5/-30", which I also don't know the meaning of. Bryan 03:34, 28 August 2006 (UTC)

As explained in footnote 2, * means a GSSP exists for that boundary. 630 +5/-30 means the prefered date is 630 Ma, but the possible range is 600-635 (ie. asymmetric error range). Dragons flight 03:38, 28 August 2006 (UTC)

[edit] How do they know how old the rock layer is?

The answer might be in the text, but I can't seem to find it. Anyway, how do they know how old the rock layer is? I ask this because creationists argue that the rock layers are dated by circular reasoning. They say scientists state the rock layer is as old as the fossils located in that layer. But then they state that the fossils are dated depending on the layer it is found it, hence the circular reasoning. Also they state that the layer can't be dated by how deep it is found because the mineral deposits could have formed quickly in a short period of time. It's an interesting catch-22, so I'm curious.

Is there a method to date the layer using some absolute dating method? Inforazer 15:24, 25 September 2006 (UTC)

This is a standard creationist claim, that like most creationist claims has little or no basis. The geologic column (that, is the releative age of strata and fossils) was determined prior to the theory of evolution by basic geological techniques such as comparisons between strata types and order of the strata. Absolute times are generally then derived by radiometric dating. The only thing remotely close to the creationist claim is that sometimes a fossil in location A may be dated by some method (such as radiometric dating) and then when the same type of fossil shows up in location B we can get a rough idea how old the B location is even if we don't have a direct method of dating the B site. Similarly, if we know that animal X lived after animal Y in the fossil record and X then shows up elsewhere with Z that gives us some rough data about Y and Z's relationship. I hope that explain the matter. JoshuaZ 16:43, 25 September 2006 (UTC)

[edit] Can we improve readability?

The article currently reads: "Evidence from radiometric dating indicates that the Earth is about 4,570 million years old (expressed with m.y.a. or "Ma" as in "it dates from 4570 Ma")."

While this is technically correct, most people do not speak this way. If something is thousands of millions of years old, they usually say it is billions of years old. Since I am new to the article, I wanted to raise the issue here first. How about saying it is 4.57 billions of years old (4.57 Ga)? RonCram 13:49, 15 December 2006 (UTC)

By the way, I have been informed by a friend that Ma stands for Mega-annum (thousands of years), Ga stands for Giga-annum (billions of years) and Ea stands for Exa-annum (quintillions of years). So the definition in the article should be corrected as well. RonCram 13:53, 15 December 2006 (UTC)

"Billion" is an ambiguous word meaning either 109 or 1012 depending on the linguistic history of the region, which is why we try to avoid it. Ga is unambiguous but still generally needs to be introduced. I agree though that the sentence is somewhat stilted. Dragons flight 13:57, 15 December 2006 (UTC)

[edit] No such thing as "basin groups", "Imbrian" or "Nectaran" eras for Earth.

The Earth's geologic time scale does not include a "basin groups", "Imbrian" or "Nectarian" era. This is pure fabrication. I propose that these references be removed. Also, the term "basin groups" is not applied to the Moon either. This is either an archaic informal term, or inaccurate information propogated by the popular press and web. I will soon be proposing for deletion the {{Hadean Footer}} template, as well as the topic Basin Groups (see lunar geologic timescale). Lunokhod 18:58, 14 January 2007 (UTC)

I agree. Hadean itself of course is a valid unit for Earth, endorsed by the International Commission on Stratigraphy, which is more or less the ultimate say-so for Wikipedia, I guess (even though they spell it "Hadian"). Cheers Geologyguy 19:19, 14 January 2007 (UTC)
I removed the offending material. However, I have little confidence that the rest of the table is correct! Lunokhod 20:20, 14 January 2007 (UTC)
I'm pretty sure (not positive!) that the rest of the table and the child pages are consistent with the ICS nomenclature, which is as close to international agreement on this as there has ever been. Cheers and thanks - Geologyguy 20:34, 14 January 2007 (UTC)
It was not there last time I saw the timeline.--JyriL talk 14:49, 16 January 2007 (UTC)
The base of the "Imbrian" and "Necaran" eras for the Moon are based on the stratigraphic marker of ejecta from the Imbrium and Nectaris basins. How could one possibly use this stratigraphic marker to subdivide relative geologig time on Earth? Lunokhod 15:19, 16 January 2007 (UTC)
If the names refer to time, it is no problem, just as "Permian" can apply to time periods worldwide. If the names refer to rocks, that's another story. Geologyguy 15:23, 16 January 2007 (UTC)
Sure, I agree, but consider this: The age of the Nectaris basin is not well known. It was once thought to be 3.92 Ga, but now some are suggesting an age of 4.1 Ga. The important point is that this controversy does not affect the lunar geologic timescale, because it was constructed on stratigraphic principles! In my opinion, applying lunar terms to Earth implies that there was some commonality of processes occurring on both bodies during the time interval. This has certainly not been proven to be the case (though some have suggested that both planets experienced a "spike" in the cratering rate between the Nectarian and Imbriam era; this is controversial). Lunokhod 15:46, 16 January 2007 (UTC)
  • I guess my only thought (now that I see, as Bejnar points out, that the Hadean lunar subdivisions are flagged as unofficial for earth - I missed that earlier) is that throughout the Earthly geologic time scale WP has been quite consistent in using the ICS nomenclature, even though some reputable sources such as those Bejnar cites (also, Paleos [2]) do use them for divisions of earthly time. But with the "unofficial" marking it is not really awful, I guess, just slightly inconsistent in not adhering to ICS like the rest of it does. No strong feelings either way, as long as usage is clear. Cheers Geologyguy 04:27, 16 January 2007 (UTC)
  • Let's try to be consisted and follow the ICS nomenclature. If the lunar periods are not used as Hadean periods even unofficially among experts, then there is no point to mention Earth in the articles. The Hadean footer template is therefore redundant and can be removed.--JyriL talk 14:49, 16 January 2007 (UTC)
  • I have added this sentence to the footnote in the table concerning the Hadean: The Hadean has also sometimes been called the Priscoan or the Azoic. Sometimes, the Hadean can be found to be subdivided into the Cryptic, Basin Groups, Nectarian, and Lower Imbrian eras (the latter two of which are based on the lunar geologic time scale), but this practice is not too common. Please feel free to change this if it is not clear. Lunokhod 11:21, 17 January 2007 (UTC)

[edit] Basin Groups article proposed for deletion.

The Basin Groups article (discussing a purported lunar or terrestrial geologic era) had been proposed for deletion. Please leave your comments on the appropriate page.Lunokhod 10:35, 15 January 2007 (UTC)

[edit] Epoch link in "Graphical timelines" is irrelevant

The link to "epoch" in the "Graphical timelines" section of the article seems to lack a purpose. It links to a disambiguation page, which, when referring to geological time, links to "Era", which is not the same thing as an epoch, epochs are a small part of eras. Should not this link be removed, as epochs are explained later in the article? Or perhaps link to lower in the page to the table of geologic time? There is no such page concerning only epochs in a specifically geological sense, so there should not be a link to a disambiguation page.Yelling Bird 02:30, 16 March 2007 (UTC)

[edit] recent Nature article

This article should probably incorporate the recent Nature article that argues (based on molecular and fossil data) that many mammalian lineages arose in the Cretaceous period and didn't diversify until about 10 - 15 million years after the dinosaur extinction. Matthias5 13:47, 29 March 2007 (UTC)

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