Talk:Geologic ages of earth history

Article Checklist for "Geologic ages of earth history"

Workgroup category or categories	Earth Sciences Workgroup [Editors asked to check categories]
Article status	Developing article: beyond a stub, but incomplete
Underlinked article?	Yes
Basic cleanup done?	No
Checklist last edited by	--Nereo Preto 03:55, 3 June 2007 (CDT)

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Headings

Thomas, standard top-level headings are two equals signs; bold is not necessary. The reason it's two and not one is that single equals signs produce headings that are the same size as the title of the article --Larry Sanger 21:23, 15 April 2007 (CDT)

Hi Larry, Right. Caught that after I had switched them back. Thought it was my oversight. But I reverted them. All article headings start at double equals and work down from there. Thanks for the tip. - Thomas Simmons 14:33 18 April, 2007 (EPT)

Introduction section

Changes made--Re: This “The geologic history of the earth is preserved and documented in the rocks. The oldest earth's rock known is more than 3 billions of years old; since this remote time, the rocks provide a record of the events on our planet, which becomes increasingly complete approachin present time.”

as opposed to this

“The geological ages refer to periods of marked change in the processes and events in the entire history of the earth. These changes have been delineated by physical evidence found in the earth’s lithosphere. Ages are also noted in reference to the types of organisms found in the fossil record down to the present day. Changes are marked by (but not exclusive of) such processes as volcanic activity, flooding, and seismic activity.”

is more of a simple overview. Referring to age as ‘documented’ is much too ambiguous and serves as a metaphor, not an accurate description. Furthermore, it does not delineate what age is as does the original paragraph. As an overview it does work in that it begins by making references to common perceptions. It does leave the reader with very little else.

I have reinserted the deleted paragraph in that it extends the replacing paragraph by defining meanings referred to in the first. --Thomas Simmons 20:36, 3 June 2007 (CDT)

Change title to 'Geologic time scale'?

Could we change the title of this article? To "Geologic time scale", I suggest. There are at least two reasons for this.

First, the description and classification of geologic time is usually found in Geologic time scales (what I also mean is that books about this topic are traditionally titled "Gologic time scale <year>", e.g., Gradstein F.M., Ogg J.G. and Smith A.G., 2004, A Geologic Time Scale 2004, Cambridge University Press).

Second, age has, in stratigraphy, a precise meaning. Strictly speaking, the article "Geologic ages of earth history" should thus be a list of ages.

This article is quite important for Earth Sciences. It might evolve into a description of the geologic time OR to a timeline of event in geologic time. I'll contribute soon (as soon as I can find the time). Thanks for starting it, for now! --Nereo Preto 01:57, 18 April 2007 (CDT)

The segmentation of time described, and the names of each segment, are not confined in their use only to geology. Biologists would also use many of these time classifications. Particularly within the study of Paleontology. Could this article be called the 'Classification of times'? Derek Harkness 04:53, 18 April 2007 (CDT)

Ok, let's do this: I'll take the time to collect some references and I'll post here soon some text about what could be this article about, and what should be its correct name in my view. I'll try to stick to authoritative sources. Then we'll discuss about it on the base of sources (of course, everyone who believes he has an argument is welcome to contribute! Don't take my step as something like "I'm the expert, shut up" please!)

The article of course can evolve under its current name for the moment. I suggest, however, to take a look at chronostratigraphy, where I posted a table with all divisions of geologic time. Related articles may be also useful (see links there). --Nereo Preto 11:17, 18 April 2007 (CDT)

The further the title gets from the actual topic, the more obscure it becomes and the less likely it will be spotted by the general public. The alternatives are semiotic artefacts of the sources which means if the reader is not familiar with the topic (one reason for coming here) they will miss these key words generated by very specialised literature. Redirects, however, are the best answer since they will fit a multitude of reader-contexts. If the literature shows a common use, then we simply put up a redirect. Piece of cake.

The limitations of the topic--in this case, geological--are the focus of the topic, but branching articles will of course make specific distinctions as would, say, palaeontology. The very names of the eras and other categories indicate a cross-disciplinary work--Phanerozoic, for example, refers not to rocks per se but about the evidence of life-- fossilised. Hence the conjunction of two disciplines in the study of the non-living and the living. If the title becomes too ambiguous it will literally loss meaning to all but those who read the books the editor has perused. Not an efficient way to communicate with the reader in my view.

I had this very problem with the article on the Eastern Orthodox Church. I listed synonyms and made redirects and Robert is Your Mothers's Brother. Thomas Simmons 17:07 19 April, 2007 (EPT)

Did the redirects. If you input Classification of times or Geologic time scale you will get to Geologic ages of earth history - Thomas Simmons 17:51 19 April, 2007 (EPT)

I believe this does it for now. Thanks Thomas. --Nereo Preto 10:05, 20 April 2007 (CDT)

I changed the introduction, quite radically actually, but maintaining some of the previous text. I believe it is improved. Can anyone take a look? (Thomas Simmons?) --Nereo Preto 13:06, 3 June 2007 (CDT)

What is this article about?

I read more carefully the article and I got confused about its function. What is this article about?

• If the article is about subdivisions of geologic time (without reference to absolute time, i.e., subdivisions which have a name regardless to their duration in millions of years), than we are talking about chronostratigraphic units
• If the topic is the numbers, i.e., how many million years ago a certain event occurred, then we are talking about geochronometry
• If this article is intended at the description of geologic time, both in terms of its subdivisions, absolute ages and definition of subdivision boundaries (e.g.: the Cretaceous-Tertiary boundary may be defined by the extinction of Dinosaurs), then the argument is the Geologic time scale.
• If instead the article is intended at a description of what happened through geologic time, then there is no name for it, but I suppose it would be something like "timeline of geologic time".

The reason I am so nitpicking -sorry about that- is the International Code of Stratigraphic Nomenclature (find it here, under "stratigraphic guide"). The existance of such a code implies that some concepts of stratigraphy (as the first two of the list above) have an official name that cannot be changed. In other words, if we refer to, e.g., chronostratigraphic units and call them the Geological ages of the earth, every expert will stigmatise our article as wrong (and there will be no room for discussion).

The meaning of "Geologic time scale" is not encoded, but it is implicit in expert's use. Check out: Gradstein F.M., Ogg J.G. and Smith A.G., 2004, A Geologic Time Scale 2004, Cambridge University Press, Cambridge, UK. This is the latest work about the topic, and is at present used as "the Bible" among researchers and students. Brief description of the work here.

I believe we must take a decision on which part, or concept(s), of stratigraphy we want to put in this article. Then it can be properly linked to other existing articles. Most important, we'll then be able to file it under a proper title. --Nereo Preto 10:53, 20 April 2007 (CDT)

We'll probably want to cover all four (and manybe more) aspects you described. However, are they all mutually exclusive. Could the article discuss more than one aspect. Even if they are exclusive, could they simply take independent sections within the whole article. Are not several of your devisions simply different views of the same item.

What is the article about? (part 2)

Lots of lists out there that purport to be about geologic ages. The lists are generated from and by many sources. Some of them do not coincide with the ICS for example. In other words, there is agreement and disagreement in that they are presented differently.

So, on the one hand you want to present what is accepted or at least debated by those in the know and possibly avoid if not relegate nonsensical, unfounded or outdated to their proper categories. In the meantime, what is the reader looking for and what are our limitations?

• Point One: Subdivisions of geologic time (relative to each other) are listed here with reference to absolute time in millions of years or fractions thereof (which does not detract from relevant disciplines in that it illustrates their overlap), and their names—which originate from a multitude of sources and for various reasons (e.g. it was first studied in this place, there were these types of flora and fauna at that time as is evident from these fossils, etc.)—and the varying aspects of nomenclature (e.g. subdivisions which have a name regardless of their duration in millions of years). They can then be elucidated in the appropriate way here and then explained in detail in a linked article on, for example, chronostratigraphic units. That said, assuming that I am reading the comments above correctly, it makes no sense to people who are living in the here and now (and measure time as humans are wont to do) to simply list the strata without reference to time—we will leave them with more questions than answers and put them off the topic. To that end, we put events into context. It is a daily thing that we are comfortable with. So, not at all sure why these strata (listed as they are by the ICS with their relative time spans by the ICS) would be listed otherwise. It is about the ages of the earth.

• Point Two: The same can be said of geochronometry

• Point Three: So yes, it is at first glance about geologic time scale and obviously there is relevance to stratigraphy and geochronometry which will be elucidated in those articles.

• Point Four: As a “timeline of geologic time”, it serves to introduce a plethora of disciplines and as such is a portal to those disciplines. I can not imagine an in-depth discussion of this in one article, it would be huge and surely exceed the limitations of a normal article. It serves to delineate ages and their classification and broad but pertinent aspects.

Geological age here and its relation to stratigraphy is an expedient and certainly an accepted one. The article is an accounting of, an overview actually, the concept of the age of the earth and how it is delineated. Then you go into sedimentology, chronogeology, stratigraphy, relative and absolute time and so forth. If it is too limited, if there is no place for the hypernymic "supercategory", the generic and conceptual, it loses cultural and thus textual coherency and would simply exist in a semiotic vaccum. This then must serve as a primer. The issues or aspects are illuminated much like a map and does not have the capacity to go into great detail which must surely be explained elsewhere.

I am not at all sure what the sentence "The meaning of "Geologic time scale" is not encoded, but it is implicit in expert's use." I say this since all language is encoded. Language is by definition a code. Symbols, both orthographic and phonetic, stand for other things. In fact the more implicit it is, the more embedded the coding. Technical jargon is very much encoded coding. Thomas Simmons 12:15 20 April, 2007 (EPT)

OK, I thing I understood what you mean. You say "The article is an accounting of, an overview actually, the concept of the age of the earth and how it is delineated" and this is almost the concept of "Geologic time scale", plus some cultural excursions around it.

You are also pushing for a writing style that can be understood by the beginner in Earth Sciences. I agree, this is a topic of wide interest and the article is an opportunity to offer scientific culture.

What I'd like to do, however, is to keep language as close as possible to scientific correctness. So for example, for students of Earth Science there are two meanings for "age": one is the fundamental chronostratigraphic unit (Age (geology)), the other is the result an absolute datation, e.g., a radiometric datation, and is a number (e.g., the Induan age begun ca. 252 Ma, where "252 Ma" is a radiometric age). So "Induan" is and age, but if we write or suggest that also "Triassic" is an age, this is an error: "Triassic" is a period. This was the reason I posted, in the beginning, some brief articles as Age (geology), so they could be used to build an article like this one.

The average reader will not get the difference between age and period perhaps, but a reader with University instruction could notice it, and could dismiss the whole article as "uninformed". We must try to satisfy also that reader, I believe. --Nereo Preto 04:15, 21 April 2007 (CDT) (continues below inserted comments from Thomas Simmons)

Could not agree more. At some point it becomes possible the beginning reader will want to pose informed questions and the language then becomes paramount. Disambiguation is also a step in the right direction as is the need to divest them of misconceptions. So, yes, beginner's language-->expert's language transitions would be very constructive. Thomas Simmons 13:14 22 April, 2007 (EPT)

About differences between sources. The rules in the International Guide of Stratigraphic Nomenclature MUST be obeyed. The way one defines, names, revises and eventually publishes, e.g., a chronostratigraphic unit is coded. If one's don't follow those rules, it cannot get published and his work is dismissed (this is the way things go at present). There are some residual "informal" chronostratigraphic units from past which are still in use, but they are becoming scarcer, and all specialists know they are going to be estinguished.

The International Guide of Stratigraphic Nomenclature hasn't a definition fot Geologic time scale, so the use of this term is somehow less rigid. However, the authors of the latest time scale give this definition:

The geologic time scale is the framework for deciphering the history of the Earth and has three components:

• The international stratigraphic divisions and their correlation in the global rock record,
• The means of measuring linear time or elapsed durations from the rock record, and
• The methods of effectively joining the two scales.

I believe this definition matches your view on this article quite well. I'll assume, as an editor, this is what you (we) are writing about.

--Nereo Preto 04:15, 21 April 2007 (CDT)

I am all for making this comply to national standards. Would not have it any other way. - Thomas Simmons 13:33, 22 April, 2007 (EPT)

What is the article about? (part 3)

With regard to, "So "Induan" is and [sic] age, but if we write or suggest that also "Triassic" is an age, this is an error: "Triassic" is a period. This was the reason I posted, in the beginning, some brief articles as Age (geology), so they could be used to build an article like this one."

I take your point and to that end I have pursued the accepted nomenclature. However, the Triassic period is explicitly defined by ages and thus a determined period of time with margin of error factored in of course. But this is the connection that students make. If we need to elucidate this factor then so be it. - Thomas Simmons 13:40, 22 April, 2007 (EPT)

Regarding eonothem and erathem, do we have a definition we can use? - Thomas Simmons 14:14, 22 April, 2007 (EPT)

Yes. Stratigraphers make a distinction between time and rocks deposited during that time. A interval of time is a geochonologic unit, while the body of rocks formed during that time is a chronostratigraphic unit. The two categories of units have different names, as in this table:

Chronostratigraphic units	Geochronologic units
Eonothem Erathem System Series Stage Substage	Eon Era Period Epoch Age Subage

Thus, the Mesozoic erathem is the body of rocks formed during the Mesozoic era. --Nereo Preto 03:35, 22 April 2007 (CDT)

A; That is a cool table. Looks great. Elucidates an important distinction. Shall we put it in? B: The words themselves are not in any dictionary I can find so I am guessing it is Latin? Have not looked it up in a Latin dictionary.- Thomas Simmons 22:22, 22 April, 2007 (EPT)

Tables of time/rock units

I copied tables of the time/rock units from chronostratigraphy, in order to avoid the spelled lists of Periods, Epochs, Ages... it seems to me more readable.

DO NOT CHANGE THE FILLING COLORS! Those colors are codified and, though the exact RGB values may change, there is a >50 year consensus on facts as, e.g., the Cretaceous is green and the Jurassic is blue. Geologists are strange people sometimes, I must admit... I know some writings are invisible; I suppose we could change the color of text, but how to do it? --Nereo Preto 15:08, 21 April 2007 (CDT)

I'd also like to move all absolute ages into the tables. It can be easely done by adding a column with the absolute age of the stage/age lower boundary, but it would be more fancy to have the numbers right on the boundaries, perhaps outside the table itself. Is it technically possible? --Nereo Preto 15:36, 21 April 2007 (CDT)

Colour--NO ARGUMENT FROM ME! : ) If they establish a standard that is acepted then I am a big one for coherency. The text colour is a problem though. Archean and Eoarchean are unreadable, most entries entries from Statherian are difficult, Permian and half of the epoch and stages are difficult to unreadable.

Absolute ages--would be nice. I have had mixed sucess with these tables. Do we have a manual? I'd practice if I had somewhere to do it and a list of possible colour codes. Thomas Simmons 13:27, 22 April, 2007 (EPT)

Text colour--Just tried various permutations in a sandbox with no luck. I seem to be able to change everything including background colour and table configuration but not the text colour. - Thomas Simmons 14:00, 22 April, 2007 (EPT)

May I suggest using border colors for the table rather than background colors. This will maintain the white background behind the text and so prevent reading problems e.g. A very crude example (needs some polishing)

Eon	Erathem/Era	System/Period
Archean	Neoarchean
	Mesoarchean
	Paleoarchean
	Eoarchean

Remember a very high percentage of men have some degree of color blindness. Particularly blue/green. We should be very carefull when placing text on a colored background or when using colored text. Derek Harkness 21:23, 21 April 2007 (CDT)

This makes it. Thanks Derek! --Nereo Preto 03:37, 22 April 2007 (CDT)

Definitely. Ta Derek. Good point. Looks great. - Thomas Simmons 22, 22 April, 2007 (EPT)

Tried to change this. Not sure what I am missing but the borders were not always complete and it looked messy. - Thomas Simmons 22:40, April, 2007 (EPT)

Tried it this time with 15 instead of 10 px. Got a more consistent colour border. (It is overlapped in some areas though so it is not uniformly the same thickness.) But the lettering in some boxes overlaps into others with the result that the red on red is still happening. If at all possible, can we go to bigger black lettering. The border's do look good though. Thomas Simmons 22:49, April, 2007 (EPT)

Tried bold face and it helps a bit but the colours will still need contrast.--Thomas Simmons 05:59, 22 April 2007 (CDT) + 18 hours

OK. A little slow but I got there. Turns ut the double brakets are what marks it for red lettering. I removed the double brakets, simple as that. Let me know if that is going to work since the colour scheme is still intact. A for bold markup, some are and some aren't and since I do not know the significance I left that alone. --Thomas Simmons 06:35, 22 April 2007 (CDT) + 18 hours

I couldn't see the changes you made so can't comment on why the borders weren't working. However, the double brackets are also what makes the names into links. Before making a appearance desision, we should decide wither we want to link those words to other articles. Many of the names do not appear else where on the article so it would make sense to link them in the table. Also, the Jurassic is still a little difficult to read. Black on dark blue never works well. Derek Harkness 09:13, 22 April 2007 (CDT)

Ooooh yeaaa. Let me amend that earlier statement--reeeeal slow on the uptake. I'll put them back. (What a git!) - --Thomas Simmons 17:18, 22 April 2007 (CDT) + 18 hours

OK, how about this. Double bracket them when we get a stub at least for the name? --Thomas Simmons 17:20, 22 April 2007 (CDT) +18 hours

Did the stub for Cambrian (Geology). Linked the table entry and . . . its blue on green. --Thomas Simmons 17:46, 22 April 2007 (CDT) + 18hours

I'll have a fiddle with the tables backgrounds/borders and text colors tonight. Editing HTML and CSS is what I'm good at, so leave it to me to do that an you can concentrate on content.

It's normal practice to leave links red if they don't have a stub yet. The red link reminds us an article needs to be written and it's possible to search for wanted pages. If you don't make red links then it's not clear wither your want an article or not.

Also note the policy on stubs is to not make stubs just to turn links blue. Work in more detail on each article. See CZ:Introduction_to_CZ_for_Wikipedians#On_stubs_and_lists for detail. Derek Harkness 23:58, 22 April 2007 (CDT)

Links in tables: what about this?

System/Period	Series/Epoch	Stage/Age	Span in millions of years ago
Cambrian→	Series 1→
		Stage 2→
			534.6 to 531 mya
			542 to 534.6 mya
		Stage 1→

--Nereo Preto 02:18, 23 April 2007 (CDT)

Links must contain text. It goes against the w3c accesability guidelines. It also prevents proper indexing for searching the site as the text within the link is used to categorise the page being linked to. I've finnished work, so I'll have a play and see what I can come up with. Derek Harkness 06:19, 23 April 2007 (CDT)

OK, think I have it tweeked:

Eonothem/Eon	Erathem/Era	System/Period
Proterozoic	Neoproterozoic	Ediacaran
		Cryogenian
		Tonian
	Mesoproterozoic	Stenian
		Ectasian
		Calymmian
	Paleoproterozoic	Statherian
		Orosirian
		Rhyacian
		Siderian
Archean	Neoarchean
	Mesoarchean
	Paleoarchean
	Eoarchean

The main changes to border-collapse: separate; border-spacing: 0px;. This stops the table border colours overlaping as the wikitable style has border-collapse:colapse set on it. In my first example I'd used a html table, not a wikitable, so was not affected by wikiformat defaults. If you give me the thumbs up, I'll do the other larger table too.Derek Harkness 06:58, 23 April 2007 (CDT)

Another more compact version:

Eonothem/Eon	Erathem/Era	System/Period
Proterozoic	Neoproterozoic	Ediacaran
		Cryogenian
		Tonian
	Mesoproterozoic	Stenian
		Ectasian
		Calymmian
	Paleoproterozoic	Statherian
		Orosirian
		Rhyacian
		Siderian
Archean	Neoarchean
	Mesoarchean
	Paleoarchean
	Eoarchean

Derek Harkness 07:28, 23 April 2007 (CDT)

This last is the most fancy. I would go for it. --Nereo Preto 09:56, 23 April 2007 (CDT)

I'd be happy with either. They really look good. --Thomas Simmons 22:46, 24 April 2007 (CDT) + 18 hours

Already done. Put the last example onto the main page. I notice the colours of Jurassic, Holocene and Pridoli are very faint. I know the rgb values are not fixed, how much can these colours be darkened before they become wrong? Derek Harkness 00:42, 25 April 2007 (CDT)

Mm... though question. I believe a little color change should not be a problem, as long as the look of the table (i.e., color hue, darkness relative to adjacent time/rock units) is maintained. Scientific publications not always stick to the exact RGB color scheme also. On the other hand, those faint colors do not look so bad in my monitor. Not wonderful, but still readable. --Nereo Preto 13:12, 3 June 2007 (CDT)

Absolute ages in schemes

Something like this, I mean...

Is anyone able to do something like this with schemes of time/rock subdivisions? It would be great. The alternative is to add a column to the tables with the absolute age of beginning for each subdivision, in Ma (million years ago). This latter solution would be, however, much less fancy. --Nereo Preto 13:19, 3 June 2007 (CDT)

P.S.: an example of one more column is in the thread above, green-colored. I don't like it much. --Nereo Preto 13:23, 3 June 2007 (CDT)

List of perfectable things...

I am (slightly) passing this article throughout, to clean it up and make it look great. I open here a list of things that could be better. Add to list if you find problems, or strike the point if you find a solution!

Introduction

1. Geological ages in common use. Could we have one or more references for the common use? --Nereo Preto 10:35, 9 June 2007 (CDT)
2. refers to marked changes... at odds with boundaries are placed at completely arbitrary positions --Nereo Preto 10:35, 9 June 2007 (CDT)

Schemata/eons/Phanerozoic

1. Table: is someone able to put the ages on? (see Absolute ages in schemes, above) --Nereo Preto 10:37, 9 June 2007 (CDT)