So all the water on earth came from comets?
Not
all of it necessarily, but likely most of it. Notice that the inner planets (Mercury, Venus, Earth and Mars) are rocky, while the outer solar system mostly consists of gas giants. Outside of Neptune's orbit, we have the Kuiper belt, which is a massive cloud of dwarf planets like Pluto, and lots and lots of comets. Most never wind up entering the inner solar system - but all it takes is a massive object (another comet, a large asteroid, etc) to knock a comet or three or twenty into a new trajectory that may bring them into the inner solar system.
Remember also that we're talking about
billions of years, a length of time that's difficult for the human mind to really grasp. The solar system
today looks much different from the solar system of a billion or two years ago - the massive bodies of Jupiter and the other gas giants do a great job of capturing any smaller stray objects. Those icy moons I spoke about were very likely Kuiper belt objects themselves, which became trapped by the gravitational pull of Jupiter or Saturn, etc, and happened to arrive in a stable orbit (this is the case with most of the moons of gas giants).
Imagine, then, if a Kuiper object the size of
Europa collided with Earth.
It seems slightly more reasonable than suggesting god did it.
It's more than that: "goddidit" is not a useful explanation. It doesn't actually
explain anything; it proposes no mechanism whatsoever for
how the water arrived, it simply assigns responsibility to the deity of your choice. That's not scientific. Science attempts to describe the mechanisms by which the universe works, as observable by our senses. Instead of saying "magic," scientists say "we don't know - yet" and proceed to try to find an actual, plausible mechanism supported by observable evidence to explain the unknown phenomenon.
In this case, Kuiper belt objects are observably real, we have evidence that comets do impact planets, and evidence suggests that impacts were far more common in the past (geologically and atmospherically inert bodies like the the moon show us how common impacts used to be, since their craters never disappear - and even Earth bears the signs of some very large impacts despite the fact that our geological and atmospheric activity mean that any impacts we can see on Earth today are relatively
young). It's a plausible mechanism supported by evidence that actually offers an
explanation rather than an assignment of credit. That makes it a
far more reasonable solution than "goddidit."
Do you suggest anything I should read rather than Wiki? Just seems like a lot of comets to me is all. So massive too. I dunno?
Take a look at the
Wiki entry on Europa:
quote:
it is predicted that the outer crust of solid ice is approximately 10—30 km (6—19 mi) thick, including a ductile "warm ice" layer, which could mean that the liquid ocean underneath may be about 100 km (60 mi) deep.[25] This leads to a volume of Europa's oceans of 3 1018 m3, slightly more than two times the volume of Earth's oceans.
Compared to this moon, we don't have much water at all. "A lot of comets" is a relative judgment - "a lot" compared to what? "Massive" compared to what? Remember, Earth itself isn't all that large compared to most of the planets in the solar system, and it's absolutely tiny compared to most of the planets we've discovered in other solar systems. Our human sense of scale becomes meaningless when we talk about astronomy. This is why "it seems to me" and other subjective personal feelings are rather meaningless in science - this case is a perfect example of something that normal human experience (and thus "common sense" reactions) simply doesn't cover.
quote:
Why would you ever be surprised that Earth has water?
I am not surprised. I just want to know where the heck it all came from. I mean I am overwhelmed by the amount of water at theme parks(water parks). This is not a grain of sand compared to the vast amount of water on the earth. The amazing size of the comets that carried water to earth. Only 1-3 of them could have fit into one of these water parks. If something this massive crashed into the earth several hundred times wouldn't it be like 1000 nuclear bombs? I just pulled that number out of a hat.
If a single object with the entire mass of the oceans crashed into Earth, yes - the kinetic energy would be equivalent to (insert obscenely large number of nuclear warheads here). The same amount of energy would be released with multiple, smaller objects as well - it would just be spread out over the multiple impacts.
But the Earth has suffered such massive collisions before. The moon is thought to have been the result of a massive body impacting Earth and fragmenting the planet; gravitational accretion eventually resulted in a much changed Earth with the moon orbiting it. There was a time when the entire Earth was a molten ball of slag. Accretion and collision is how the planet formed in the first place, after all.
It had to be awesome! Now I agree the fact I am unable to visualize in my mind that this is how it happened has no impact on reality. I don't think I am spinning at 1,000 mph ATM. So, is this really how it happened? Comets the length of 5-6-7-8 school buses long weighing what millions of pounds crashed into earth with the explosive force of bombs then melted?
Rather than saying "that's how it happened," I'd rather say "that's the explanation that best fits the evidence we have currently." Remember, science doesn't tend to make claims of absolutes. Rather, we use a sliding scale of sorts where our degree of certainty in the accuracy of a given theory increases as additional evidence supports it; theories supported by lots of evidence with very accurately verified predictions are counted as extremely accurate (ie, General Relativity, the Theory of Evolution, etc), but absolute proof is the realm of mathematics.
Also, I'd lose the specifics regarding the size of the objects colliding with Earth. Yes, the current model states that Earth's water is the result of watery objects impacting the planet, but we can't say exactly how large or how many - any evidence of those sorts of specifics have long since been destroyed by ongoing geological processes. We know that there was plenty of time over the formation of the solar system for many, many impacts to have occurred, and we know that icy bodies are pretty common. That's really all we need to know.