Talk:Cambrian (geology)

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 Definition First geologic period of Palaeozoic time stretching approximately from 550 to 480 million years BP. [d] [e]

G'day,

Here is the Cambrian introduction. The tables are situated so that comments and discussion can be more easily placed for each series. --Thomas Simmons 19:37, 22 April 2007 (CDT) + 18 hours

At this time, getting specifics about the Cambrian from the ICS is problematic since the web site for the Cambrian Subcommision is not up. Most if not all the other sources available are referring to the older nomenclature or regional nomenclature. The officla and globally defined information as such will have to come in as it is available. --Thomas Simmons 19:43, 22 April 2007 (CDT) + 18 hours

Regarding reference to EarthTime: This organisation has been referred to by some of the Subcommission reports and is used as a coordinating body to calibrate earth history. --Thomas Simmons 20:19, 22 April 2007 (CDT) + 18 hours

"Cambrian"

I'm no geologist but I am a stickler for how English is used. The first sentence says, "The Cambrian is both a system of strata and a period of time." This is a claim about how the word "Cambrian" is used. The Cambrian itself is not both one thing and the other (as if ambiguous words created ambiguous entities), but rather, the word "Cambrian" names both those things. I think it would be better in any case to define one, and then the other, if you are going to have an article that includes both. But I do wonder whether it would be better to have an article titled Cambrian Period and another titled Cambrian Strata. Surely there are facts about one that are not immediately relevant to the other. Isn't it the case that you're combining the articles mainly because they share the word "Cambrian" in common? But the strata is very different from the period.

I appreciate the work--please don't get me wrong, I couldn't create this without doing lots of research--but this article, and others about other eras or periods, should be more accessible than this one is at present. They should open with information that helps "locate" the period with respect to things people might be familiar with--such as dinos, or sabertooth tigers, or primordial ooze. If there is some biological or geological fact that really distinguishes an era, that, too, should be in the lead. The point is that in every article about an individually nameable thing (this is an individually nameable time period), after a description, we immediately turn to what is notable about it.

--Larry Sanger 00:13, 23 April 2007 (CDT)

It took awhile but I went ahead and cleared this up. --Thomas Simmons 20:55, 6 June 2007 (CDT)

I also have a question about the title. Are there other meanings for "Cambrian" except that of geology? If so, may the title simply be "Cambrian"? And, if the title is going to remain this, should "Geology" be capitalized? In other articles I used lower case. Well, minor things of course. The start is great. I plan to contribute. I plan to add material to this article about the "Cambrian explosion", i.e., the beginning of life as we know it. Then I suppose the article becomes notable. --Nereo Preto 02:27, 23 April 2007 (CDT)

As for caps, that is just habit I guess. Cambrian (geology) is fine. Certainly if it is usual and customary here. Strata versus period--not sure here. The two are congruent. I am not finding references that show them to be different (other than the usual variations) and they are juxtaposed by the governing body ICS. The article could be split drawing attention to the distinctions and similarities. I will work up definitions and go from there.--Thomas Simmons 16:39, 25 April 2007 (CDT) +17 hours


My Point is, if you study strata you study physical distinctions, make hypothesis about process etc. If you study period you may use dissimilar instrumentation, getting dates, establishing elemental ratios, etc and refer to the fossil record. The point being if you talk about one, you will employ a lot of information about the other and vice versa. They are not just complementary; they are extensively interconnected and defined by some very arcane differences

Stratigraphy is the study of the formation, composition, and sequence of sediments, characteristics and attributes of rocks (formation, composition) as they are in strata (sequence of sediments), and the interpretation of strata in terms of derivation and geological background. The field encompasses study and validation of stratification; the analysis in the vertical, time dimension, of a series of layers in the horizontal, space dimension. (It is often used as a relative dating technique to assess the temporal sequence of artefact deposition.) The field is strongly interrelated to other fields like anthropology, archaeology and paleobotany. and defined by stratigraphic paleontology. Both fields draw their definitions from the other. Systems (layers of rock) are laid down during periods (time-span).

Examples here from the Geological Society of London (which is now about 200 years old I think):

  • Stratigraphy: the study of the ordering of rock units.
  • Stratum (pl. strata): unit of sedimentary rock, bounded by bedding planes and having reasonable lateral persistence. A layer of rock.
  • Formation: a unit of rocks which is. consistently recognizable over wide areas and which is therefore useful in mapping.
  • Period: the time-span over which a geological system was laid down. The time-unit corresponding to a known body of rock defined by stratigraphic palaeontology.
  • System: the rocks laid down during a Period (Carboniferous, Jurassic, etc.) The Cretaceous System was created during the Cretaceous *Period. Defined by stratigraphic palaeontology.

Source: Geological Society of London [1]

Getting into geochronology gets even more technical. An article is surely necessary but will have to branch off into sub-articles given the complexity of the field. Most folks can relate to sinking a metal tube into the ground and pulling out a long column of mud and stones, noting the differences in colour, composition, fossils etc—these are evident to anyone who has walked past an outcropping thrust up by seismic activity of worn through by erosion. But geochronology is really very involved and employs very arcane definitions and technical jargon that is beyond the reach of the average reader (e.g. laser ablation) At this point, it seems to me to simply note the differences and go into the technical side of it in depth as we have the time is an efficient strategy. --Thomas Simmons 18:06, 25 April 2007 (CDT) +17 hours