Re: alpha christians
Not-That-Bright said:
Why are the sun's rays even dangerous to us? God's such a jerk.
great answer
ok, to explain everything up to the formation of the earth (i'm astrophysics, not biology, so i'll leave that part to someone else)
we started off with hydrogen gas (90+%), primarily, with some helium, deuterium, and a little lithium (very little)
thanks to gravity, the gas condensed in some areas of space. in some areas, it would condense with a large enough mass that the pressure at the center of it was enough to allow fusion to occur, first making helium from hydrogen, and from there progressing up through higher and higher element masses. when something has enough mass to have fusion take place, we call it a star.
for smaller elements, fusion releases energy. in other words, putting two hydrogen atoms together causes energy to be released. This is directly related to Einstein's E=mc^2. When a significant amount of helium has been made, the star will then move up to the next element....i believe generally going to Berylium, Carbon, Nitrogen, Oxygen, etc. The heaviest element that can be formed this way is Iron, because energy is needed to make anything heavier than Iron.
At this point, two things happen. A smaller star, such as the Sun, will start to release the outer layers, releasing elements up to iron back out into the universe and then shrink down itno a white dwarf. Significantly larger stars explode in what is called a supernova. The extraordinarily high energies involved in a star's explosion are the source for the energy to create all elements heavier than iron.
Now, the first generation of stars couldn't have had planets like the earth because at that time, the universe didn't contain anything to make a terrestrial planet with. However, we're in approximately the 3rd generation of stars now, and so by now there has been time for the elements that the earth needs to have been made by the two processes discussed above.
As for the formation of the earth itself, a cloud of gas and particles will, in time, develop a spin to it, leading to the material forming a disk. at the center is where the mass density is greatest, and here is where the star forms. further out on the disk, small particles continuously collide and clump together over time, leading to the formation of planets. so its not "two rocks hit together" but many many many small particles all accumulating over time.
In the inner solar system, the solar wind from the sun was able to blow away most of lighter elements, such as hydrogen and helium, so we're left with primarily heavier elements, nitrogen, carbon, oxygen, etc. In the outer solar system, the solar wind is weaker and so gases remained there long enough that masses could form that would be big enough that they could hold the light gasses in their gravity, and so the gas giants were formed.
Further out yet are the most distant elements, which include the Oort Cloud and the Kuiper Belt (of which Pluto is a member). these objects were formed at the birth of the solar system, and tend to be rock and ices (both water ice, and other ices, such as carbon dioxide). A good example of these objects are comets.
At this point in the solar system's lifespan, comets are relativly rare, as are other objects that cross the paths of the planets. However, in the early solar system, there were a great many and impacts were common, and an early earth would have been constantly bombarded. From these numerous impacts of comets and other objects from the outer portions of the solar system came the water that the earth now has, as those objects are a good source of water.
as for why the earth is the only planet in our solar system we know of that can support life....if the sun were less luminous, Venus could, and if Mars was the size of the earth, it feasibly could as well. To say "well, why's the earth the place that has life" is the same as to say "why are my keys in the last place i looked?"
we're on the earth because it IS the life-supporting one...but had it been mars instead we'd be there going "why is mars the only planet that has life?
