Talk:Hadean
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[edit] New Hadean Page
My fingers itches very hard to rewrite the Hadean page, so I'm starting it on the Hadean Outline page. rursus 04:20, 18 October 2006 (PDT)
[edit] Initial Tellus Formation
The section The Dynamics of the Hadean should be split into parts.
- 1. Defining or describing The Hadean as a "transformation of earth from gaseous cloud state to solid state" is like explaining that "king Gustavus Adolphus of Sweden died from mist" - which is kind of true but very misleading.
- 2. But Hadean is not entirely Pregeologic. If it be, there would be a great risk that Hadean would shrink to nil-nada as geologists discover older strata. Rather Hadean, being an informal not stratographically defined eon, could (?) be informally referred to as "the eon when astronomical creation processes had an immense impact on the creation and formation of Earth". My wager is that humankind will end up with a Hadean defined like:
- from the creation of Earth, to the end of the LHB (Late Heavy Bombardment)
I believe the event scheme of Prehadean/Hadean is as follows:
- 1. 4567 Ma Supernova "Germinator" exploded causing a gravito-thermal collapse in the Sun Nebula;
- 2. ???? Ma The planetesimal system formed, soon giving rise to
- a. a number of protoplanets in the inner solar system, out to and including the current asteroid belt distance from Sun,
- b. the jovians Jupiter, Saturn, Neptune and Uranus, and
- c. the outer solar system icy planets (like Pluto).
- in this era there were some 10-20 heavy FUor eruptions from Sun in its T Tauri stage, rising temperatures by 700? Kelvin;
- 3. For 10-30 Ma the inner solar system was characterized by protoplanet collisions and terrestrial planet formation: Mercury, Venus, Protogaia (protoearth), Theia and Mars. I've read one dating of Protogaia's formation to be 4557 Ma, which might be after Sun's T Tauri eruptions (??) - this would then be one possible starting point of Hadean; most certainly Protogaia evolved some atmosphere soon after it's creation.
- 4. 4533 Ma For a time after formation Protogaia was moonless, until Theia had grown to the size of current Mars. It is believed Theia was in Lagrange 4 coorbit (preceeding Troian = same orbit but 30° forth) with Protogaia, but that position became unstable as Theia grew. Then Theia collided with Protogaia, and the major part became Earth, while some debris came in orbit around earth and assembled to Moon in some 10 years. It's very unclear whether this collision removed the atmosphere or not, I've read some simulation numbers indicating that it's a 50:50 whether removed or not removed. In either case the impact created a silicate atmosphere that is supposed to have cooled very fast (decades);
- 5. XXXX Ma Earth outgassing and cooling now permitted liquid water.
- note that at high atmospheric pressures water is liquid at high temperatures, f.ex. at 2.7 bar water boils at 130°C,
- note that LUCA often are believed to be near termophiles,
- note that the closeness of Moon would create massive crustal tides - which would affect plate tectonics.
- 6. very approximately 4100-3950 Ma Some orbital instability of the jovians started the Late Heavy Bombardment (LHB). One (simulation supported) scenario says Jupiter and Saturn (slowly) migrated into a mutual 1:2 resonance which made a formerly stable jovian system chaotically unstable. The chances that Uranus and Neptune would change places with each other would according to similar theories be 50%. This jovian system disruption would cause
- a. Jupiter cleaning up the zone of the current asteroid main belt, inner planets being heavily bombarded by asteroids,
- b. Neptune running straight into the zone of outer solar system icy planets, there wreaking havoc, creating a similar but much more intense bombardment within the jovian system, including of course the jovian icy moons. Neptune captured the former icy planet Triton in a retrograde orbit at that time.
- 7. the LHB declines inversely exponentially, so that by c:a 3800 Ma the impact levels reaches "normal" - whatever that is supposed to mean...
rursus 04:39, 13 October 2006 (PDT)
[edit] The Primordial Atmosphere
The Primordial Atmosphere is not a majority concept of current solar system theories. It is in a way presuming a gas accretion theory, which is most often considered obsolete and wrong for the terrestrial planets, f.ex. Earth, where solid planetesimal accretion is favoured nowadays. rursus 04:40, 13 October 2006 (PDT)
[edit] Virtually no cometary water
The text (3rd para) says: "An initial steam atmosphere formed of water from comets and hydrated minerals...". The comet source is disproven, isotope composition of water implies virtually all must have been from hydrated minerals. rursus 13:46, 13 October 2006 (PDT)
[edit] Several alternative options
Okay first of all the Hadean isnt a subject I know much about, so I'm not really qualified to comment authoritatively one way or another. However several alternatives might be suggested:
One option would be to have the main Hadean page as a short non-controversial page, with links from there to the two different accounts (Rursus' page and the original Palaeos com page), with a notice on each that the subject is controversial, and to see the other page for the alternative point of view.
Another option is to have Rursus' page as the main Hadean page, and the original page as another page which it links to.
Still another option would be to combine the two accounts in one page, or better a numbre of Hadean pages, according to subject, giving each position and then the counter-view in each section to provide a wikipedia-style NPOV
What does everyone else think? M alan kazlev 02:31, 19 October 2006 (PDT)
[edit] No such thing as "basin groups", "Imbrian" or "Nectaran" eras for Earth.
- I've revomed the table containing referenced to "basin groups", "Imbrian", etc. These time periods do not exist for the Earth! Mark Wieczorek : 10:03, 15 January 2007 User:82.230.60.81
- I have restored it. For Earth geology, these period names may be unofficial, but they are used: see for example http://en.wikipedia.org/wiki/Acasta_Gneiss . Anthony Appleyard 22:27, 20 April 2008 (PDT)
