Talk:Hadean

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What does "after they were dep" mean? -phma

According to the author(s) of the current entry: "The term Hadean seldom occurs. W. B. Harland has coined an almost synonymous term: the "Priscoan period"." I have encountered the term 'Hadean' many times, and never 'Priscoan'. An informal Google check shows 'Hadean' (23,100) being used 25 times more often than 'Priscoan' (923). Seems the author of that sentence is pushing a terminology agenda for some reason. In other words, exaggerating or outright lying.

Let's assume good intentions and not make hasty accusations. If you check this link you will find neither of those terms, rather the new term Eoarchean for the earliest era. The International Commission on Stratigraphy is changing the rules or the names. The link above is the current status of the officially accepted nomenclature. Popular searches such as Google won't return many hits for the newly proposed official version. Vsmith 23:33, 25 July 2005 (UTC)
From my experience most astrobiologists use the term "Hadean". I personally never heard of the term "Priscoan" and I do research directly applicable to the Hadean ocean (though I guess it shows a good deal of ignorance on my side). --Asmirnov 07:44, 24 February 2006 (UTC)

The link shows a timeline starting at 3600 Ma. Hadean has traditionally referred to the period of time starting at ~4500 Ma or whenever the Earth actually formed. Regardless, synonymizing 'Eoarchean' with 'Hadean' is inconsistent with the geologic charts provided on Wikipedia with the definition of Hadean and even Eoarchean itself, and the associated 'followed by' / 'preceded by' links and notes. Even if it is the 'correct' terminology the charts should be made consistent with the text before Eoarchean is defined in the text to cover the same period, unless it is clarified that this is not the same thing as a synonym (Eoarchean has 'no defined start', but in a chronology where both terms coexist Hadean would be defined to end before Eoarchean begins). I do believe from experience that the usage of Hadean is current, regardless of the wishes of any commissions.


Contents

[edit] intersting info someone might like to check out

anu research It is evidence for a major rethink of the Hadean era. Have fun kids The bellman 09:07, 30 November 2005 (UTC)

  • Mark Harrison, and others, in the above research studied hafnium isotopes derived from lutetium radioactive decay and found indications of a continent within 100 million years of the formation of the Earth (4.25-4 Ga). A molten Earth should not have cooled that quickly, which implies a cool planetary formation.
  • Harrison and Bruce Watson also studied titanium in zircons and also found an age of 4.25-4 Ga, and the implication of a water ocean, which requires rather cool temperatures and an atmosphere.[1]
  • John W. Valley, and others, found zircons of age 4.4-2.5 Ga with oxygen isotopes indicating a cool Earth and liquid water.[2]
  • Other planetary formation work calculates that water molecules would have escaped Earth's gravity until a radius of about 40% of the current size, and water (and other volatiles) would have been retained after that point.[3]
  • The giant impact hypothesis assumes a lot of melting during the creation of the Moon, but much of the Moon may be from the impactor.[4] Also present composition does not match complete melting and it is hard to completely melt and mix huge rock masses.[5]
So it appears either the Hadean is misnamed or it happened very early in the planet's formation. (SEWilco 04:53, 22 August 2006 (UTC))

[edit] Azoic

I've suggested a merge of the currently-minimal Azoic Age article to here. However, I'm not sure whether it's strictly appropriate. It's my understanding that "Azoic" was used, up until the 1950's, to refer to the entire period of time now encompassed by the Hadean, Archaean, and a large part of the Proterozoic. Does someone have a definitive reference from that era (the 1950's, that is) that could be cited? Tevildo 02:56, 20 December 2006 (UTC)

There is no "Azoic" article in the 1911 EB, but there was a lot of geology science discovered/created by the 1960s. I'll see what other sources I have handy. One comes to mind and I think I know its location. (SEWilco 05:49, 20 December 2006 (UTC))
  • I would suggest extreme caution in any such merger, for the very reason you state, namely the Azoic and the Hadean are not co-extensive. In fact by some definitions of the Azoic and the Hadean they don't even overlap. Originally the Cambrian was thought to be the beginning of life, and all Pre-cambrian rocks were Azoic. Since Hadean can be read as "before the earliest known rocks", you can see the problem. Now that the term Tertiary has been depreciated, it is not appropriate to confuse the current nomenclature with the previous. Just like Tertiary needs its own article, so does Azoic. It should be an article in the history of geo-science, and focus on that. The Hadean article should focus as it does on its place in the current geologic time scale. I will look in my old textbooks for a prevalent definition of the Azoic. --Bejnar 21:34, 27 December 2006 (UTC)

I have rewritten the Azoic Age article, correcting a misapprehension, and providing references. I do not think that merger is warranted. --Bejnar 22:47, 27 December 2006 (UTC)

There was a renaming of igneous rocks in 1902.[6] Might Azoic have become entangled in this? (SEWilco 07:21, 29 December 2006 (UTC))

I did find one brief mention in 1911 EB. The Geology article at the end of Part VII says "The stratified formations of the earth's crust, or geological record, are classified into five main divisions, which in their order of antiguity are as follows: (1) Archean or Pre-Cambrian, called also sometimes Azoic (lifeless) or Eozoic (dawn of life); …". So Archean seemed more common (and is used elsewhere in the article), while Azoic was less commonly used in this book. It might be a label for the start of the Paleozoic, as earlier fossils are hard to identify and thus life seemed to begin then (during much of the early 20th century). (SEWilco 08:07, 29 December 2006 (UTC))
Do read the rewrite on the Azoic Age, and check out the footnotes which will take you into books electronically on Google Book. The term Archean replaced the term Azoic, in part because of the evolution debate. The Archean was then limited at the early end by the Hadean, and the later end by the Proterozoic. Archeozoic is another old term that you will see tossed about for (part of) this same early time. (begin smile) There remains some doubt whether there was life in the early 20th century. (end smile) --Bejnar 20:55, 29 December 2006 (UTC)
OK, I think Azoic Age can stand on its own as an article now, and I'm no longer supporting the merge - the templates can be removed after the stautory two weeks unless anyone has a different opinion. Just one point - we'll need a definite source that the renaming was "because of the evolution debate". Was there really a _debate_ in 1900? I know that the relative roles of genetics and natural selection were a matter of scientific discussion, but I didn't think that the fundamentalist opposition to evolution per se started until the 1920's. Tevildo 21:10, 29 December 2006 (UTC)
Take a look at the cartoons in Punch, the British humor magazine, at the time of Huxley's defense of Darwin. --Bejnar 02:58, 16 January 2007 (UTC)
Yes, but that was in 1860. Was there a debate in _1900_? Louis Agassiz, the last serious creationist scientist, died in 1873 - the fundamentalist movement was founded in 1910. In any case, we'll need to substantiate the claim that "the evolution debate" (rather than the normal progress of the geological sciences) influenced the renaming. Tevildo 12:27, 16 January 2007 (UTC)

I see that the merge has been proposed again. I would Oppose the merge for the reasons stated above last year. Tevildo (talk) 16:13, 11 May 2008 (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 03:36, 17 January 2007 (UTC)


131.111.243.37It is the International Commission for Stratigraphy that does not recognise the Hadean; however since there are no sedimentary rocks of this age it is not really covered by them...

[edit] What existed before.

Is there an attempt to explain what existed before the Hadean ?

At least we can work back from this period to the present but what was before the hadean ? Kendirangu 10:24, 25 May 2007 (UTC)

The point is that the Hadean is the earliest era at which it makes sense to talk about the planet Earth. Before the Hadean, there was a protoplanet that would eventually become the Earth. Before that, it was a planetesimal (or possibly a variety of different ones that together made up the protoplanet). Before that, it was a discrete ring of dust. Before that, it was an undifferentiated part of the protoplanetary disk. These phases together are probably only a few dozen million years long.
Prior to that, the Earth was part of the even more undifferentiated solar nebula, which may have lasted for a very long time until a nearby supernova caused a shock wave that sped its rotation, flattening it into a disk and jump-starting the Sun.
See History of Earth and solar nebula for details. --216.15.6.87 12:29, 19 September 2007 (UTC)