History of Earth and the Solar System
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A Former User last edited by
Who has interest in astrophysics, palaeogeology and palaeobiology, this thread is for you:)
Geologists have organised the history of the Earth into a timescale on which large chunks of time are called periods and smaller ones called epochs. Each period is separated by a major geological or palaeontological event, such as the mass extinction of the dinosaurs which occurred at the boundary between the Cretaceous period and the Paleocene epoch.
Archean era: 3.8 billion–2.5 billion years agoCryogenian period: 850 million–635 million years ago
Ediacaran period: 635 million–545 million years ago
Cambrian period: 545 million–495 million years ago
Ordovician period: 495 million–443 million years ago
Silurian period: 443 million–417 million years ago
Devonian period: 417 million–354 million years ago
Carboniferous period: 354 million–290 million years ago
Permian period: 290 million–248 million years ago
Triassic period: 248 million–205 million years ago
Jurassic period: 205 million–142 million years ago
Cretaceous period: 142 million–65 million years ago
At this point of the Earth's history we have the extinction of dinosaurs, after which mammals begin to evolve rapidly.
The page linked to doesn't cite the period started at 65Ma ("megaanni" means 'million yrs ago'), instead it cites the epochs of this contemporary period -- including the last but one "Pleistocene epoch", where palaeobiology places the emergence of humans.
The last one (we live in) is the most clearly observable. It starts with the end of the last glacial period - about 11.7 thousand years ago.
Glacial periods are not Ice Ages -- strictly speaking, the last (current) Ice Age has never ended yet: so long as Earth has permanent ice-sheets (in the polar regions that is), we live in an ice age.
(One American politician claims that humankind is on the verge of ending the Age, and does seemingly oppose that;)In my next postreply, I'm thinking of delving into the very first Era. Actually, the first one above was not the very first: I'll recollect the name of that first "fire" Age and dig about some info.
So long!
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A Former User last edited by
BBC obviously suck.
Those largest periods are properly called aeons. The first Aeon (presumably before life) is called Hadean Eon. -
A Former User last edited by
From that site:
Hadean time (4.6 to 4 billion years ago)* is not a geological period as such. No rocks on the Earth are this old, except for meteorites.
I quite oppose that. Despite Earth had "no rocks" and geology is thought by many as a "rock science" (Science rocks! :haia:),
- in physical terms, rock existed at any time - literally with the first moments of that orbiting stuff clumping together, then being molten is just another state of the same substance,
- the word itself literally means "study of Earth" - not "study of rocks".
(Myself, I like Rock to listen to - not to study;)
During Hadean time, the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The relative abundance of heavier elements in the Solar System suggests that this gas and dust was derived from a supernova, or supernovas — the explosion of an old, massive star. Etc.
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A Former User last edited by
And anyway, science is not a thing that builds forever to never change.
It's like with the planets: in 2008, it was agreed that Pluto is not among the planet - belonging to the next, further orbital layer of bodies.
So, Wiki citesIn the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada, and Western Australia. Rock formations in Greenland comprise sediments dated around 3,800 million years ago and...
http://en.wikipedia.org/wiki/Hadean#Hadean_rocks -
A Former User last edited by
In my next postreply, I'm thinking of delving into the very first Era. Actually, the first one above was not the very first: I'll recollect the name of that first "fire" Age and dig about some info.
Moreover,
All Earth's geology depends on the composition and structure of the planet. This, in turn, depends on how the Earth formed in the violent beginning of our solar system. <...> To describe the early Earth, we must bring trhe processes of formation into the same framework as its subsequent geological evolution. To this end, we propose the Chaotian Eon for the time of planet formation.
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20100036717.pdf -
A Former User last edited by
And anyway, science is not a thing that builds forever to never change.
It's like with the planets: in 2008, it was agreed that Pluto is not among the planets - belonging to the next, further orbital layer of bodies.Interesting, EGU cites that "Pluto bids to get back to planetary status. "
With at least five moons and an atmosphere to its name, Pluto has some impressive stats for something that isn't a planet. A new analysis has also determined its diameter is bigger than its outer solar system rival, Eris! http://bit.ly/1ntJjvs
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A Former User last edited by
From here:
Of particular interest, Manfred Schidlowski argued in 1979 that the carbon isotopic ratios of some sedimentary rocks found in Greenland were a relic of organic matter. There was much debate over the precise dating of the rocks, with Schidlowski suggesting they were about 3800 Ma old, and others suggesting a more "modest" 3600 Ma. In either case it was a very short time for abiogenesis to have taken place, and if Schidlowski was correct, arguably too short a time. The Late Heavy Bombardment and the "re-melting" of the crust that it suggests provides a timeline under which this would be possible; life either formed immediately after the Late Heavy Bombardment, or more likely survived it, having arisen earlier during the Hadean. Recent studies suggest that the rocks Schidlowski found are indeed from the older end of the possible age range at about 3850 Ma, suggesting the latter possibility is the most likely answer.<sup>17</sup>
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A Former User last edited by
The "superscript" formatting tool seems not to work.
The "nobbc" one doesn't works either!
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A Former User last edited by
The collision ... was enough to vaporize some of the Earth's outer layers and melt both bodies. A portion of the mantle material was ejected into orbit around the Earth. ... The ejecta in orbit around the Earth could have condensed into a single body within a couple of weeks. Under the influence of its own gravity, the ejected material became a more spherical body: the Moon.
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A Former User last edited by
Are you using the forum as a personal note?!
I'm educating you
Formation of the Moon:
The collision ... was enough to vaporize some of the Earth's outer layers and melt both bodies. A portion of the mantle material was ejected into orbit around the Earth. ... The ejecta in orbit around the Earth could have condensed into a single body within a couple of weeks. Under the influence of its own gravity, the ejected material became a more spherical body: the Moon.
, in another article,This impact vaporized a large amount of the crust, and sent material into orbit around Earth, which lingered as rings for a few million years, until these rings condensed into the Moon.
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sgunhouse Moderator Volunteer last edited by
Josh is somewhat more interested in science generally than the typical forum-goer would be. Perhaps that's why they didn't like him at the DnD Sanctuary?
As far as that last post ... it's hard to imagine anything astronomical happening "within a couple of weeks". Well, when it comes to condensing anyway. If the material was ejected as a single molten blob (already "a single body") then I suppose - but it is hard to imagine that scenario. I've never seen any sort of impact produce a single large piece of ejecta; more often you see hundreds of pieces of varying sizes.
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A Former User last edited by
The collision ... was enough to vaporize some of the Earth's outer layers and melt both bodies. A portion of the mantle material was ejected into orbit around the Earth. ... The ejecta in orbit around the Earth could have condensed into a single body within a couple of weeks. Under the influence of its own gravity, the ejected material became a more spherical body: the Moon.
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blackbird71 last edited byFormation of the Moon:
The collision ... was enough to vaporize some of the Earth's outer layers and melt both bodies. A portion of the mantle material was ejected into orbit around the Earth. ... The ejecta in orbit around the Earth could have condensed into a single body within a couple of weeks. Under the influence of its own gravity, the ejected material became a more spherical body: the Moon.
One key problem with the lunar collision theory is the appearance of over 1000 lunar transient events noted during the last 350 years since the invention of the telescope. These events include observed bright spots, red spots, streaks of light, misty-looking areas, and colored glows on the moon's surface, each event covering areas smaller than several miles and lasting for but a few hours. The collision theory for the moon's origin assumes a consolidation of displaced earth crust and dust in the cold of space, perhaps causing a temporary period of radioactive-induced compressive volcanism, but one which would have died out long ago if the moon came into being 1 to 3 billion years ago. Current terrestrial geological evidence and understanding prohibits a more recent time for such a lunar-creating collision to have occurred. In other words, the necessary time-frame of the collision theory posits that the moon must currently be geologically inactive or dead, especially near its middle and upper strata regions, with residual lunar volcanism (if any) hopelessly locked deep within the innermost core of the body because of heat radiating into outer space over a billion or more years.
Yet in 1971, Apollo 15 detected high concentrations of radon-222 near Archistarchus Crater. That gas has a half-life of less than 4 days, so it had to come as a gaseous discharge from deep within the moon - implying volcanic transport activity. NASA, in its Technical Report R-277, indicates 11 sites on the moon where transient lunar events have been concentrated, particularly near Aristarchus and Alphonsus craters. In 1992, French astronomers observed a haze-like brightening near the central peak of Langrenus crater. Lunar heat flow measurements made during the Apollo missions demonstrated instances of unexpectedly high lunar heat flow. The lunar collision theory notwithstanding, something akin to volcanic activity is still occurring on the moon.
The net effect of that evidence is that, because the current collision theory for the moon's origin cannot explain the surface or near-surface volcanism on the moon, it implies such a moon-origin theory is problematic at best and incorrect at worst.
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Or perhaps I should say, talking back to to your sources?
