Talk:History of Earth

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  1. January 2006 – April 2006

Note: Now that I've finished writing the inital drafts, I'm trying to make this article extremely well-referenced. However, I am an amateur, and am not up-to-date on the latest research in the many fields this article spans. If you have additional references, or can improve on the ones I've selected, please make the appropriate changes or leave a note on this talk page. Thanks! — Knowledge Seeker দ 07:14, 3 April 2006 (UTC)

Contents

[edit] Specific reference requests

I've had relatively good success in finding appropriate references, but there are some that have me stymied. — Knowledge Seeker দ 07:18, 3 April 2006 (UTC)

  • How about citations for when Pangaea assembled and broke up? That article states 300 Ma–180 Ma. Can anyone confirm? — Knowledge Seeker দ 04:03, 9 April 2006 (UTC)
    • Unsure if this has been addressed, but the breakup of Pangaea occurred at different times. That is, not all of the continents split apart simultaneously. The ranges given, therefore, are appropriate. I believe is not necessary to address the details here as they are covered in the article for Pangaea. — Theinsomniac4life 22:03, 27 January 2007 (UTC)

[edit] Geology & climate

In response to my request for feedback on this article, I received a helpful reply. Guettarda suggested that there is perhaps an overemphasis on biology, especially once life evolves I tend to abandon geology and such. This reflects my bias as well as my knowledge state; and I've had more trouble finding information on the geologic events. As he points out, I would like to put more information on some major geologic events and climate changes, but I know little about these areas. Perhaps others can assist me with this or at least point out areas that should be included. Some that come to mind offhand are as follows:

  • Late Heavy Bombardment
  • Snowball Earth?
  • More about ice ages
  • More about continent movements such as Gondwana and Laurasia, more if I can find references
  • How climate changes might have contributed to major evolutionary events
  • Origin of some major mountain ranges, like the Himalayas

Obviously, this is an overview article, and we cannot mention all events. What am I missing? Any other suggestions? — Knowledge Seeker দ 03:20, 16 April 2006 (UTC)

I was going to make the same suggestion. I think one good way to include geology and climate would be to structure the article around the global supercontinents, especially the last three: Rodinia, Pannotia, and Pangaea. Climate and geology are intertwined, and the supercontinents exhibit that connection to the extreme. In Earth's history, the formation and destruction of supercontinents (the supercontinent cycle) are probably some of the most significant and most salient events. Other important climatic and geologic events are related to the "big five" mass extinctions (Ordovician-Silurian , Devonian, Permian-Triassic, Triassic-Jurassic, Cretaceous-Tertiary), which is another topic you could structure around. The P-T extinction is particularly intriguing; I would at least mention the Siberian Traps. bcasterline t 04:38, 16 April 2006 (UTC)
I should also mention Christopher Scotese, who has good information for a general overview and perspective. bcasterline t 04:46, 16 April 2006 (UTC)
Thanks for the feedback. I'm not sure what you mean about re-structuring the article—those three supercontinents form only a part of Earth's history; all fall within the "Colonization of land" section unless I am misunderstanding something. I'm trying not to overemphasize any period of Earth's history; I know that I have followed the progression of life for the most part but the time from the assembly of Rodinia to the breakup of Pangaea only cover a fifth of Earth's lifetime. Still, I will try to include some more information about accompanying climate changes; it is a bit difficult for me since my grasp of those details is not as good. I did try to mention each of the extinction events, but I didn't realize that the causes for them were so well-established. I don't want to get into too much detail since that section is already quite long, but I will look to expand it. I definitely do want to include more information about climate changes; hopefully you can keep an eye on my progress and suggest any material I haven't already included. — Knowledge Seeker দ 06:08, 17 April 2006 (UTC)
You're right: the restructuring would be only that one section. I think the supercontinents and/or mass extinctions form a logical chronology to work around; but restructuring might be more work than it's worth, and the switch from biology-focused to geology-focused for one section might seem strange, anyway. Finding references could also be a problem. If I have some time, maybe I'll write an alternative version of that section, and we can compare. bcasterline t 12:31, 17 April 2006 (UTC)

[edit] Future history?

I was wondering if a final section on the future of the earth would appropriate, such as the end of the world as the sun expands. I have not seen any real discussion of it on Wikipedia, other than perhaps end of planet Earth. --Stbalbach 03:14, 17 April 2006 (UTC)

It's a good idea, but I'm not sure how it would fit the flow of the article—it seems a bit out of place in a history article. I'm not even sure how much we could write without getting into too much speculation. Probably not more than a couple sentences: "Future: In five billion years, the Sun will likely expand into a red giant, destroying Earth or rendering it uninhabitable" or something like that. I think it's appropriate in the "See also", but I just don't think it fits here. See Talk:History of Earth/Archive 1#future. What do others think? — Knowledge Seeker দ 06:12, 17 April 2006 (UTC)
I've seen standard narratives of this nature, talking about when the oceans boil off, when life ends, etc.. laying out the general stages of how the planet will come to an end. I don't think it should discuss the future of humanity or civilization, which are covered in other articles. -- Stbalbach 13:56, 17 April 2006 (UTC)
This article is about Earth's history and should not include speculation on the future, especially since it's long already. I think Future of Earth would make an interesting article though. bcasterline t 15:53, 17 April 2006 (UTC)

[edit] Mass Extinctions and Large Igneous Provinces

KS: To head off a request for a reference on the recently inserted link between the Permo-Triassic extinction and flood basalt volcanic activity in Siberia I will put one here if you need it (Grard et al, 2005). I'd be happy to forward any pdfs to you if you think you would find them useful…the intro to the Siberian Traps paper has some well referenced data that you might like. In addition, if links between LIPs/flood basalts and extinctions are mentioned for one mass extinction, they should be mentioned for others. This should include links between Deccan Traps (India) basaltic activity and the K-T extinction, reference below (Wingall, 2001). There may be others...I'm not knowledgeable enough to know which are "good" correlations and which are not.

Grard, A., Francois, L.M., Dessert, C., Dupre, B., Godderis, Y. 2005. Basaltic volcanism and mass extinction at the Permo-Triassic boundary: Environmental impact and modeling of the global carbon cycle. Earth and Planetary Science Letters v.234 (1-2) 207-221. doi:10.1016/j.epsl.2005.02.027
Wingall, P.B. 2001. Large igneous provinces and mass extinctions. Earth-Science Reviews v.53 (1-2) 1-33. doi:10.1016/S0012-8252(00)00037-4

Rickert 04:10, 17 April 2006 (UTC)

Rickert, that's very helpful; I'll use it when I incorporate Bcasterline's suggestions above. — Knowledge Seeker দ 06:13, 17 April 2006 (UTC)

[edit] Civilisation section

Couple issues there

  • "As intelligence increased and language became more complex" - is there any evidence to suggest that human intelligence (whoever measured) has increased during the lifespan of Homo sapiens?
  • The article seems to suggest that sedentary lifestyles followed the beginnings of agriculutre - weren't the Natufians sedentary H-G? Guettarda 12:50, 17 April 2006 (UTC)
Thanks, Guettarda. I removed the offending statement—I think it's left over from a previous version of the paragraph which I subsequently rewrote. If you can think of anything to add to the statement, feel free. I'll poke a bit into the agriculture/nomadic relationship, but the Natufians article notes that they were unusual in founding permanent settlements prior to developing agriculture. Or am I misunderstanding? — Knowledge Seeker দ 07:00, 13 May 2006 (UTC)
According to Jared Diamond, many (maybe most) groups of people were sedentary before they adopted agriculture. Not all societies made the change from hunter-gatherers to farmers in the same way or at the same time (or at all), though, so generalizing is difficult. -- bcasterline • talk 22:58, 30 May 2006 (UTC)

[edit] History of life on earth

This article seems to be more about the subset "history of life on earth", rather than the history of the planet itself. I would have expected more than a paragraph or two on the geological development of the planet. Think about moving the title to History of life on Earth, or even History of evolution on Earth, and creating an article more focused on the history of Earth related to the physical sciences (including geology, oceanography, history of the atmosphere, near-earth environment (origin of moon from earth), etc. from the scattered articles on these topics) for the History of Earth title. . --Blainster 21:59, 23 May 2006 (UTC)

Earth is used both in a literal and metonymical sense. (For instance, History of Europe does not mention its separation from Laurasia, not to mention its prior incorporation in Pangaea, and so on.) I have tried to weave together themes from all periods of Earth's history; the origin of the moon and the oceans and such occurred relatively early in Earth's history and I have been trying my best not to let the article become too unbalanced. I'd be happy to add (or have added) information on the geological development, particularly if good references are available, and as you can see above, I'm working to add more information on climate and geological change. In my opinion, "history of life on Earth" or "history of evolution on Earth" would be poor titles for the article—the formation of Earth, origin of the moon, formation of the oceans, and so on, have little to do with the history of evolution on Earth—though I welcome others' opinions as well. — Knowledge Seeker দ 22:40, 23 May 2006 (UTC)
Consolidating all information into one article is the easiest for readers, and the title "History of Earth" makes the most sense. But, it's also true that, after "The Hadean", this article focuses on biology and mentions geology and climate only marginally. (As has been mentioned before.) One solution would be to add more information on geology and climate, but the article is long already. So, creating three separate articles would also work: History of Earth for geology, History of climate for climate, and History of life on Earth for life. Note, however, that there is already a History of life without prose. -- bcasterline • talk 23:11, 23 May 2006 (UTC)
In writing this article, my explicit aim has been to try to synthesize a narrative from numerous disciplines. I would be quite pleased if someone were to write subarticles for specific disciplines and I would be especially pleased if anyone is able to offer assistance in integrating climate and geological information into the article, but I would prefer this article to remain an overview, and to have articles with a narrower scope written separately. — Knowledge Seeker দ 02:50, 24 May 2006 (UTC)
OK, I thought it over, and will withdraw the suggestion for a title change which (in my opinion) better fits the present state of the article, and propose expansion instead. I agree that the subject History of Earth is so broad that it must be a survey article with links to other main articles. The current article is nicely written. It just seems that it is too heavily oriented towards History of Life. This seems like the right title to bring several more topics together. Part of the problem is that some of the missing pieces are only sections of articles, and others are not written yet. By adding appropriate links to the topics I mentioned in the first post, you can see some examples. Bcaster points out the importance of climate history, and I should have mentioned glaciation as well. With this in mind, I will start a new talk section to discuss suggested organization and expansion. --Blainster 05:00, 24 May 2006 (UTC)

Mentioning that one theory is supported by the majority of scientists really gives no information at all (other than sociological) and seems to serve here to deprecate a minority theory. As hindsight shows us that nearly every dearly held conviction is eventually proven wrong, I would like to see wikipedia avoid this type of rhetoric and simply provide evidence (if there is any) and arguments to contrast theories. Brallan 09:01, 16 November 2006 (UTC)

[edit] Proposed expansion/organization of the article

The article Earth science offers an outline summarized in Earth's spheres, that could be a model for expansion of History of Earth, that is, to provide sections for each of the four spheres, beginning with the lithosphere following the cooling of the earth's crust. It looks like most of this would fit between the sections on the Hadean period and the Origin of Life (even though a good share of it is contemporaneous).

Hopefully this will inspire ideas for creating stub sections that link to other fields of Earth history not yet included. I am not necessarily suggesting that the "spheres" be used in section titles, just that the topics be covered. --Blainster 05:00, 24 May 2006 (UTC)

How about mentioning supervolcanic eruptions at Lake Toba and Yellowstone, formation of Hawaii islands, Himalayas, Great Rift Valley, Grand Canyon, Berring Straits and Arizona's impact crater, Tunguska incident, formation of fossil fuel, historical record of temperature and sea levels, earth's magnetic fields, precession( Milankovitch cycles) and rate of spin, change of vegetation in Sahara and Ethiopia? —The preceding unsigned comment was added by 203.116.34.138 (talk • contribs) 20:03, May 28, 2006 (UTC)

These are some good ideas, and I'll work to try to include some when I get a chance; I'm a bit busy right now. What would especially help would be referenced material—I really want this article to be well-referenced. Peer-reviewed journals, major books, or even authoritative web pages would be useful. — Knowledge Seeker দ 04:22, 15 June 2006 (UTC)

[edit] Clock analogy confusing

The analogy of the formation of Earth between geologic time and a 24 hour clock face is very confusing. Understanding large amounts of time is no more difficult than this analogy is. Should we remove it? Astrobayes 02:48, 8 July 2006 (UTC)

Well, since I incorporated the analogy when I wrote this article, I obviously think it's a good idea. Having the day analogy helps me to see just how recent in Earth's history the 380-million-year-ago emergence of the tetrapods or the couple-hundred-millennia-ago evolution of Homo sapiens is. But perhaps I am alone in perceiving this benefit. Also, I guess I don't understand how the clock analogy is confusing. Perhaps if you explain, I could clarify the article. — Knowledge Seeker দ 02:58, 8 July 2006 (UTC)
What makes the clock analogy confusing is that I have taken the time to understand and become quite comfortable with all scales of times and numbers - it isn't easy but it is definately worth doing since you can really appreciate the physical processes taking place in physical systems when such scales are involved. So, having become very comfortable with billions, millions, etc. it is quite unnatural to compare geologic time with clock time and in fact is a detriment to the education of individuals on such a subject. For example, when you're in chemistry class, calculating the number of moles in a volume of some sample the instructor does not dilute the concepts by making such numbers as 10^23 more palatable through an analogy to something "more familiar" to a general audience. Since Wikipedia aims to be encyclopedic it is therefore wiser to present the geologic time as a scientist would, and let the readers take the time to understand and appreciate such timescales rather than using an analogy that a scientist would not (in fact, a length analogy would work better here, using the length of a meter stick to represent the time from the beginning of the Earth's formation until today - and I would happily do the calculations for this article using this particular analogy). That's my professional opinion. Finally, I commented on this article because I'm a physicist in the Wiki:Physics project and this article was listed for request of peer-review. So, I'm offering to the editors of this article my professional peer-review: the clock analogy is confusing, not used by scientists, and so therefore should not be included in this encyclopedic article. Cheers, Astrobayes 03:13, 8 July 2006 (UTC)
I also disagree. The clock is an aid -- it's not used in stead of geologic time (so many years ago), it's used in addition to it. I think the clock analogy is fairly common and, to me, makes a lot more sense than comparing time to length, or anything else. I don't see how it hurts those familiar with geologic time (myself included), but I see how it could help someone who's not. -- bcasterline • talk 03:40, 8 July 2006 (UTC)
I know this was a little while ago, but I think the clock analogy is a good idea. As I was recently reminded by one kind Wikipedian, not every one has recieved higher education and for many people concepts which are simple and obvious to us are confusing or simply meaningless. I, also, am used to thinking in time-scales of millions and billions of years, but for many people such massive numbers are meaningless, in the same way that the size of this planet is meaningless when you never see it from above- see how vast the world is and how tiny we are. Wikipedia is as much for newcomers to subjects as for proffessionals, and the analogy does neatly put things into perspective. Weenerbunny 09:42, 12 August 2006 (UTC)
But there is another analogy which accomplishes the same goal, just as neatly, and doesn't use a scale of the same physical dimension (i.e. using seconds to represent billions of years - which is just completely awkward). I propose that we use a simple meter stick rather than a clock - in fact this is how many students first learn to deal with geologic time. In this case, we're dealing with small segments of the meter stick representing billions of years, and not seconds representing billions of years. And as geologic time progresses, we trace the meter stick from left to right. here's an example, and here's another, and another. In fact, the article on Geologic Time does just this. So why would the present article use a completely different analogy than the main article on the topic uses? That's a bit inconsistent isn't it?
And one final note, has anyone actually sat down and done the calculation for the time conversion in this article to see if the original author's scale is consistent? My guess is probably not. My guess is that everyone just reads the article and nods their head, taking all the numbers for granted when in fact the numbers are not consistent with a constant time conversion. And if the conversion is inconsistent then isn't using "clock time" as an analogy for geologic time rather a poor choice? My concern is simply that in a desire to present something "easy" or "digestible" we've accepted something that doesn't consistently represent the process. I'd like to go with the meter stick analogy, but if we keep the clock analogy we need to verify the math - no source for the calculations is cited. Your thoughts? Astrobayes 01:45, 19 August 2006 (UTC)
The clock analogy is the same as it appears on the National Geographic Channel on several programs on the history of the earth, which I would assume is reliable. Also I find the analogy to be excellent when explaining these things to people. It's easy to realize scales when you know the universe took 3 days to be created and human beings have been on earth for less than a second and dinosaurs lasted half a minute. Sabar 10:56, 21 August 2006 (UTC)

I don't particularly like the clock analogy either; it feels like I'm being talked down to, and it intrudes in a lots of places. It also is a little weird to encounter it when you jump to a specific section; not everyone is going to be reading the entire article from start to finish. It is worthwhile to try to give people a sense of scale and an overall picture of events. Why not simply have a pie chart showing the various periods? I think much of the problem of comprehension is that some people have a harder time digesting numbers - whether that's millions of years or seconds on a clock. A graphic would be much more intuitive, I think. -- Beland 21:06, 4 September 2006 (UTC)

I agree that it is a bit intrusive, especially if you don't read the article from top to bottom - most people do not do this with most articles they come across, while a larger number of people *do* sit through an entire television program, which is why the clock analogy works so well on the Nat'l. Geographic channel, but is at the same time so cumbersome in what could be a great article like this. It is human nature to skim something for the most salient points, and it bears considering this when improving this article. I had not thought of the pie chart idea but that is a really good one, and one I would support. I also am a fan of the old classic "meter stick" idea. As Beland states, some people have trouble with numbers, whether or not they are large or small, but everyone has an intuition with a "pie chart" or a "meter stick." Just something to consider. Cheers, Astrobayes 18:35, 5 September 2006 (UTC)
    • I agree with Beland, I think the clock analogy is very bad. It's confusing mainly because no conversion factor is given, and it collapses the time period too much. "Our clock"? ON my clock, the earth formed 4.5 billion years ago, and no 12am is going to cut it. --Lucifer arma 05:30, 23 March 2007 (UTC)

8 8 8 8 8 8 8

I think the clock analogy is perfectly clear: it is used extensively in many general texts, and employed by science journals like Scientific American all the time. Are they all guilty of being "confusing"? I can't understand Astrobayes' reasoning. On the one hand, it is "confusing" to break down unthinkable eons of time into segments of something we all experience - a day - but then he does not feel any need to make material easier for non-experts - it's up to them to buckle down and digest the technical stuff. An encyclopedia is a GENERAL reference book, not a text for specialists. Let's remember who is looking up Wikipedia, and write for them, instead of showing off for our peers. There is just far too much of this in Wikipedia. The expert or would-be expert has a mountain of scholarly articles available to them, and they know where to find it. The average person is not so lucky. To write cogently and clearly for the non-specialist is much more of a challenge than just spraying technical material everywhere, most of which a lay person does not require in order to understand a subject. Please consider why it is that professional writers for journals like Scientific American and New Scientist can provide information on cutting edge science that is accessible by ordinary readers, while the "People's Encyclopedia" is riddled with obscurantist tracts that presume that the reader has a college degree in a subject, or at least should be aiming for one if they have the temerity to be reading about it. I have spent 20 years writing and editing technical material intended for non-professional users. Frankly, the biggest headache I had were "experts" on board trying to preserve the cachet of their subject by insisting on the inclusion of technical minutiae by the score. They would have been exactly the sort of people who fought tooth and nail to keep academic writings in Latin during the Middle Ages, and I would have paid good money to have them off any project I was on. abzorba 10:16, 2 October 2006 (UTC)

It is of course a matter of preference. I have stated my case for using a meter stick rather than a clock but if the marjority of readers find the clock analogy works well, I am certainly in favor of keeping it the way it is. The accessibility of this article is a huge concern, and the clock analogy doesn't change the content or science in the article itself, so if it works... it works :) Cheers, Astrobayes 23:20, 2 October 2006 (UTC)

A timeline would be more appropriate for this article. If you add a timeline as a graphic aid the flow of the text won't be interrupted with this analogy and you won't be confusing readers who haven't read the introductory paragraph. When I first read this I thought the page had been vandalized and someone had put exact times next to the pre-historic dates as a joke. Please explain how this confusion is better than simply providing a timeline. Jagget mcfew 04:39, 9 November 2006 (UTC)

There are several reasons I selected the clock analogy over a timeline. It is difficult to portray the entire range of events on a single timeline; many events happen during the last few million years. It is not possible to show them all. The way this is usually circumvented is by either showing a logarithmic scale, or by using a series of timelines with successively narrower ranges. Both are useful approaches, but what my intent is in this article is to really give people a feel for the time spacing of these events. I have no objections to someone creating and adding a timeline, and perhaps that will help some people see this better. But for people like me, and those I consulted when I began writing this article, changing the scale of time to reduce it to an interval the brain can easily grasp lets us see the temporal relationships in a way that timelines can't. There are several timelines on Wikipedia, and if you like, I can place notices to them at the beginning of the article. But I feel that this scale reduction helps make this material accessible for people who perhaps are not as well-versed in mathematics and the sciences as many Wikipedia are, and that's why I wish it to stay. — Knowledge Seeker দ 05:40, 23 March 2007 (UTC)

[edit] This is an outstanding article

This is one of the best articles I've ever read on Wikipedia - kudos to the writers. The analogy is absolutely fantastic, and the tone of the article is perfect for understanding. — Deckiller 06:08, 20 September 2006 (UTC)

[edit] Edit suggestions for History of World

[Hello, Knowledge Seeker, Myles325 (abzorba) here. I am a medically-retired writer of manuals, with extensive experience in both creating and editing work of an essentially educational nature. Since discovering Wikipedia, I have become very interested in it, both for what it offers educationally, and for the concept in general. I read your comment on my note in the talk section of Timelines for Biological Evolution, where you suggested I look up this article. I must say that I am very impressed with both articles and would like to do some work on them. Because "History of the World" is quite long, I thought that a good way to proceed would be to post my corrections here, for by yourself and interested parties, prior to going any further. I am going to do this now. My comments on the text are in square brackets]

8888888888888

[The changes in the first couple of sections are mainly stylistic, except for the deletion of the word “impossible”, used once in a way that I cannot recognise.

The History of the Earth covers approximately 4,567 billion years (4,567,000,000 years), from Earth's formation out of the solar nebula to the present. This article presents a broad overview of this period, with summaries of leading scientific theories where they pertain to the events described. Large intervals of time can be difficult to comprehend so the analogy of a single 24-hour period has been employed, beginning 4.567 billion years ago, with the formation of the Earth, and concluding in the present time . Each second of this period represents about 53,000 years. On this scale, the origin of the Universe, which occurred about 13.7 billion years ago with the Big Bang event, took place almost three days ago—two whole days before our clock began to tick. Origin of the Earth

Artist’s impression of a protoplanetary disc forming around a star, as seen from a distant planet.

[I do not think you should make mention of binary stars. There is are sufficient terms here for the novice to absorb without pressing unnecessary ones upon him].


Earth formed as part of the birth of the solar system: what eventually became the solar system initially existed as a large, rotating cloud of dust and gas. It was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements produced by stars long gone. Then, about 4.6 billion years ago (fifteen to thirty minutes before our imaginary clock started), this vast cloud of dilute gas began to contract, possibly because a nearby star exploded, becoming a supernova and radiating shock waves into the gas. This contracting cloud became the solar nebula: its centre would become the sun. As the cloud continued to rotate, gravity and intertia caused the roughly spherical shape of the gas cloud to flatten into a shape more like a rotating discus, the proto-planetary disc. Gas and dust falling inward toward the centre of the disc became hotter as friction between the particles increased, until the matter at the centre was sufficiently concentrated for nuclear fusion to begin, igniting the fire that would create a new T Tauri star, our early Sun. The Sun's internal heat source came through its conversion of hydrogen into helium, the process of converting one element to another called nucleosynthesis, which releases vast amounts of energy.

Meanwhile, as gravity caused matter to contract, the remainder of the disc started to break up into rings. Small fragments collided and fused into larger ones..[2] One such agglomeration was approximately 150 million kilometers from the center: Earth. Others became the planets. As the Sun continued to contract and heat, fusion began, and the resulting solar wind radiating outward swept away most of the material in the disc that had not already condensed into larger bodies.

On the origin of the Moon there is still some uncertainty, although there is considerable evidence for the giant impact hypothesis. Earth may not have been the only planet forming 150 million kilometers from the Sun. It is hypothesized that another agglomeration of dust occurred 150 million kilometers from both the Sun and the Earth. This planet, named Theia, is thought to have been smaller than the current Earth, probably about the size and mass of Mars. Its orbit may at first have been stable but destabilized as Earth increased its mass by the accretion of more and more material. Eventually, Theia collided with Earth at a low, oblique angle.,,[3] about 4.533 billion years ago (perhaps 12:05 a.m. on our clock). The low speed and angle were not enough to destroy Earth, but a large portion of its crust was ejected. Heavier elements from Theia sank to Earth’s core, while the remaining material and ejecta condensed into a single body within a couple of weeks.Under the influence of its own gravity, and probably within a year, this became a more spherical body: the Moon.[4] The impact is also thought to have changed Earth's axis to produce the large 23.5° axial tilt that is responsible for Earth's seasons. (A simple, ideal model of the planets’origins would have axial tilts of 0° with no recognizable seasons.) It may also have sped up Earth's rotation and initiated the planet's plate tectonics. [Suggest deletion of refs to Langrian points, and precise mechanics of collision. Not necessary here. Link to Moon should suffice]

The Hadean eon The early Earth, during the very early Hadean eon, was very different from the world we know today. Oceans did not yet exist, and there was no oxygen in the atmosphere. The surface was bombarded by planetoids and other material left over from the formation of the solar system. This bombardment, combined with heat from radioactive breakdown, residual heat, and heat from the pressure of contraction, caused the planet to be fully molten. Heavier elements sank to the center while lighter ones rose to the surface, producing Earth's various layers (see "Structure of the Earth"). Initially, Earth's atmosphere would have been composed of surrounding material from the solar nebula, especially light gases such as hydrogen and helium, but the solar wind and Earth's own heat would have driven off this first atmosphere.

A new atmosphere began to develop as the Earth increased in mass to about 40% of its present radius, with the stronger gravity better able to retain an atmosphere which included water. As the high temperatures attending the birth of Earth declined, a solid crust began to accumulate on the surface, re-melted in places by impacts from the bombardment of asteroids, much more prevalent in the early Solar System than now. Large impacts would have caused localized melting and partial differentiation, with some lighter elements being brought to the surface or released to the moist atmosphere. [5]

The surface continued to cool quickly, forming a solid crust within 150 million years (around 12:45 a.m. on our clock).[6] From 4 to 3.8 billion years ago (around 3 to 4 a.m.), Earth underwent a period of heavy asteroidal bombardment.[7] Steam escaped from the crust while more gases were released by volcanoes, completing the second atmosphere. Additional water, later to become the sea, came via bolide collisions, probably from asteroids ejected from the outer asteroid belt under the influence of Jupiter's gravity. The planet cooled. Clouds formed. Rain gave rise to the oceans within 750 million years (3.8 billion years ago, around 4:00 a.m. on our clock), but probably earlier. (Recent evidence suggests the oceans may have begun forming by 4.2 billion years ago-1:50 a.m. on our clock.)[8] The new atmosphere probably contained ammonia, methane, water vapor, carbon dioxide, and nitrogen, as well as smaller amounts of other gases. Any free oxygen would have been bound by hydrogen or minerals on the surface. Volcanic activity was intense and, without an ozone layer to hinder its entry, ultraviolet radiation flooded the surface.

Beginnings of Life [This material is of very high quality. It requires little further amendation.] […except that it is good practice to spell out what DNA stands for, even if you do not intend to define or describe it] [The first cell - Similarly, very good. But if you are going to talk about the history of DNA and RNA and their relationship, however briefly, then you do need to spell them out, and make a note of what they are]. [This is as far as I have progressed. At this stage, I might wait for some feedback before I go further.]abzorba 06:19, 4 October 2006 (UTC)

[edit] Peer Review Request

Was there a request for Peer Review of this article? Are editors still interested? If so, put a note on my user page and I will be glad to do it. I have a background in geology and marine biology, but currently study paleobotany and plant systematics. KP Botany 23:02, 17 December 2006 (UTC)

Why ask, instead of just looking at the article? (SEWilco 05:33, 18 December 2006 (UTC))
As I posted on your talk page, other articles requesting Peer Review had boxes on their talk page mentioning this--this page does not. If someone has already done it, there's no need for me to. Critically PRing a science article takes a lot of time. KP Botany 16:27, 18 December 2006 (UTC)

[edit] Needs MUCH more on geologic evolution

Echoing earlier comments, I think the basic material presented here is quite good and gives a nice synopsis of the origin of the planet and the subsequent evolution of life on the planet. BUT... it does not really address the guts of what most professionals think of as Earth History. Earth History includes the origin and evolution of life (after all, evolution is an observed fact of the fossil record -- Darwin just came up with an explanation for how it happens). But a great deal of earth history involves the formation of continents and their movements, the super continent cycle (eg Pannonia, Rodinia, Pangea), atmospheric evolution and its effect on geochemical cycles, the snowball earth hypothesis, global glaciations (Neoproterozoic, Permian, Pleistocene), and more.

I agree with other comments that the article is too long to go into all of these issues in detail, but the balance issue needs to be addressed -- especially since many of them relate directly to evolution of life on earth (e.g., links between early life, oxygenation of the atmosphere, and the formation of banded iron formations, or Pleistocene glaciations and the rise of modern homo sapiens). And anyone looking here for a real history of the earth will be dissappointed.

IF people do not feel that separate ariticles on Earth History (Biologic evolution) and Earth History (Geologic) are the way to go, then i suggest augmenting the current article with brief discussion of the major geologic aeons (Hadean, Proterozoic, Phanerozoic) inserted at the appropriate point in the evolution of life discussion. Thus, eariest cells after Hadean discussion, the Proterozoic discussion followed by rise of eukaryotes, the Phanerozoic discussion followed by complex life. Super continents were all mostly Proterozoic except Pangaea. Snowball earth was late Proterozoic, and the connections between impacts/large igneous provinces are all Phanerozoic. This will preserve the timeline approach that works so well in current article.

To save space, many of these issues can be alluded to briefly with link to whatever articles discuss in more detail.

I will think about this and await feedback from others. I have some other stuff i am working on now and see no need to hurry on this. Geodoc 04:04, 23 January 2007 (UTC)

This article is about past geologic events. See Earth for links to articles about the planet (including this article). See Biology for links to articles about biology (including History of biology. (SEWilco 17:28, 23 January 2007 (UTC))
Everything I discuss refers to past geologic events. Hadean = 3.8-4.5 Ga, Proterozoic 3.8-0.5 Ga, Phanerozoic 0.5-now. So this comment is puzzling. Geodoc 02:46, 24 January 2007 (UTC)
Please feel free to augment the article with additional information on Earth's geologic changes. I put in what I could when I wrote this article, but I am limited by knowledge, which is limited mostly to biological changes. As I have commented above, I would appreciate some integration of geological and climatological changes into the article. — Knowledge Seeker দ 17:42, 19 March 2007 (UTC)
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