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The article doesn't explain what caused the initial angular momentum in the pre-solar nebula. If gravity was the only force acting in the early stages of solar system formation, wouldn't material in the proto-cloud simply have flowed inward toward an expanding gravitational center? Virgil H. Soule (talk) 17:59, 21 August 2012 (UTC)
Only if the pre-solar nebula were perfectly still and collapsed directly. However, there are random motions in any star forming cloud (they're highly turbulent beasts) which means the gas has angular momentum when compared to the gravitational center. Just a little bit of random motion a large distance from the gravitational center is a lot of angular momentum. I'm not sure how or where this should go into the article, and I don't have an immediate ref, though one should be pretty easy to find. —Alex (ASHill | talk | contribs) 00:15, 22 August 2012 (UTC)
We say, "In one billion years' time, as the Sun's radiation output increases, its circumstellar habitable zone will move outwards, making the Earth's surface too hot for liquid water to exist there naturally. At this point, all life on land will become extinct. Evaporation of water, a potent greenhouse gas, from the oceans' surface could accelerate temperature increase, potentially ending all life on Earth even sooner."
From what I understand, that's not what we think will happen. In about a tenth that time, the increasing solar output will increase the height of water vapor in the atmosphere until it reaches the stratosphere, where it will dissociate and the hydrogen will be lost to space. In another 100My the oceans will be gone. Earth will thus loose its water long before surface temperatures would otherwise be too great for liquid water. — kwami (talk) 16:03, 3 October 2013 (UTC)
if that's true, a source would be really helpful. Most of the sources I have read say that the threat to life in hte next gyr is not ocean depletion, but CO2 starvation. Serendipodous 17:16, 3 October 2013 (UTC)
Isn't this statement in the article is a little off the mark: "The composition of this region with a mass just over that of the Sun was about the same as that of the Sun today..."?
A Wikipedia article on the sun says the sun in its lifetime has converted about 100 earth masses to energy. Solar nuclear reactions only convert about 0.7% of hydrogen mass to energy, so this means 14,000 earth masses worth of hydrogen have been fused to helium. The total mass of the sun is 333,000 earths, so during its 4.7 billion years as a main sequence star the sun must have converted 4.2% = (14,000/333,000) of its total mass from hydrogen to helium.
The third paragraph states that "The position of the planets often shifted, and planets have switched places". However nowhere in the reference used (Gomes et al. 2005) is planetary orbit switching mentioned. What IS mentioned is that orbital periods of Jupiter and Saturn crossed their mean mean motion resonance (MMR) ratio of 1:2. Figure 2 of Gomes et al. (2005) indicates that at no point during the period responsible for the Late Heavy Bombardment did the orbits of the four outer planets switch <2>. If the orbits were changed during this chaotic period, then the authors must cite the correct reference.