Life came to Earth from comet?

[Bullgrit]

I often hear/read articles that mention the theory that asteroids/comets brought water or the beginnings of life to Earth in the early stages of the solar system. (I heard one just this morning on NPR, which prompted this post.) Why are there so many theories about water/life coming to Earth from elsewhere? What's wrong with the idea that water/life started on Earth without being imported from space? And if it did have to be imported, what was wrong with Earth that it couldn't form water/life without an asteroid/comet coming in? And what was right with whereever that asteroid/comet came from that it *could* form water/life? Or did water/life start on the asteroid/comet, itself?

Bullgrit

 

[delericho]

Well, how else do you explain that all the aliens look like humans with funny noses?

 

[delericho]

But for a serious answer: no idea, sorry.

 

[Janx]

I saw one of those articles the other day.

While I wouldn't want science to limit its thinking to presume the earth is the center of the solar stsrem or the source of all life, in the case of life itself, it seems earth is more hospitable than anywhere else in our solar system.

It seems less probable that life evolved off-planet on a pretty crappy rock, when it has oodles of water and other stuff right here on Earth. Even allowing for our present day earth wasn't as awesome back when life first evolved, it seems it still couldn't have sucked as much as being frozen in the vaccum of space all the time.

It almost seems like wishful oppositional defiance thinking that since "everybody" assumes life began on earth, they must be proven wrong.

 

[Kramodlog]

Comets are important because when Earth was young and a big ball of magma, the core was forming itself drawing in all the elements toward the center. At that point Earth was devoid of most elements on it's surface.

When the surfaced cooled it prevented elements from sinking to the core, so comets with elements in them, like gold, seeded the surface.

Sounds ridiculus? Remember, when the universe and Earth were young, there was a lot more asteroid hurling in space and planets, moons, were constantly bombarded.

This is why life might come from the stars, elements needed for life came from the stars.

 

[WayneLigon]

I often hear/read articles that mention the theory that asteroids/comets brought water or the beginnings of life to Earth in the early stages of the solar system. (I heard one just this morning on NPR, which prompted this post.) Why are there so many theories about water/life coming to Earth from elsewhere? What's wrong with the idea that water/life started on Earth without being imported from space? And if it did have to be imported, what was wrong with Earth that it couldn't form water/life without an asteroid/comet coming in? And what was right with whereever that asteroid/comet came from that it *could* form water/life? Or did water/life start on the asteroid/comet, itself?

Bullgrit

There are some contending theories that even a billion years or so was not enough time for the primordial molecules to assemble and make that move from inorganic to organic; these basically try to plot Moore's Law to biological systems by regressing from current complexity to the primordial state, and come up with a time-of-origin of something like 9 billion years. A problem, since our solar system is something like 4-5 billion years old at most.

Most of the theories are not really saying 'life' but 'organic primordial molecules', kind of 'pre-life'. These can form in space itself and be propagated by the solar wind, or be hardy enough to somehow survive the 'exit-travel through space-survive re-entry' cycle of a grazing collision elsewhere.

Earth's water seems to be a balance of stuff it produced naturally, and stuff it accumulated as icy bodies were drawn in. Without knowing the composition of most Kuiper Belt objects, it's difficult to say how much may have come from the solar system leftovers.

One of the reasons that panspermia has been given an uptick in recent years is the discovery that some of our old suppositions about the formation of life - it must have sunlight, it must have water, it can only form in x-y temperatures - all that is pretty much crap due to discovering several forms of life that require none of those things and that can exist and evolve in conditions we previously thought impossible.

 

[Umbran]

Why are there so many theories about water/life coming to Earth from elsewhere? What's wrong with the idea that water/life started on Earth without being imported from space?

Well, the entire planet is imported from space, now isn't it? We're only quibbling over what part of space the water came from, and when.

The thing is, water isn't just water. Hydrogen and oxygen have isotopes. You can look at the water on Earth, and measure the ratio of isotopes in our water, and compare it to water seen in asteroids, and that seen in comets. If the isotope ratios match one or the other, one is apt to think there's a bit of a link.

It was only in the 1980s that we started getting an idea of the isotope ratios in the water of comets. And the results seemed to indicate that comets had notably different ratios than seen in our oceans, while water in asteroids looked a lot more like our water. But more recent measurements (of comet Hartley 2, for example) have shown comets with rather Earthlike water.

The basic reason folks sometimes wonder if our water came from asteroids or comets is simple: heat. The early Earth was molten - what water we had on the surface would be forced to vapor - hot vapor. And hot vapor has a tendency to escape into space. So, many figure that any water we had would have boiled off, and would have needed to be replaced.

As far as I know, there's no consensus, though. Some think our water came from comets and/or asteroids, others think it was outgassed or created (by burning hydrogen) on Earth after it had cooled enough to hold onto liquid water. Others think there's a mix of sources.

And if it did have to be imported, what was wrong with Earth that it couldn't form water/life without an asteroid/comet coming in? And what was right with whereever that asteroid/comet came from that it *could* form water/life? Or did water/life start on the asteroid/comet, itself?

Water is pretty common stuff - there's lots of it out in the Universe that we can see. Life is less obvious...

There's a basic tenet that runs through all of science - one place in the universe is pretty much the same as any other. We are not the center of the universe, the galaxy, or the solar system. We aren't the center of *anything*. Earth is not really special. So, if you think that the origin of life is an unlikely event, you have to ask if or why it happened here, specifically.

 

[Tonguez]

The thing is Earth is special, not because of water but because of fire. It has the right conditions for stable (non-explosive) ignition of fire. Further more the confluence of the iniquely large Moon and Jupiters gravity well help maintain the stability that allowed the ignition of the primordial goo that necame life.

All praise Father Jupiter and Mother Earth, and of course Sister Moon and Grandfather Sun

 

[Umbran]

The thing is Earth is special, not because of water but because of fire. It has the right conditions for stable (non-explosive) ignition of fire.

Maybe you're using the word "fire" in new and interesting ways.

But, by standard definition, no, that cannot be why we have life - we have the conditions for stable, non-explosive fire (like a burning log) because we have an oxygen atmosphere. That atmosphere was generated by living things, which began when we had a reducing atmosphere, not an oxidative one.

 

[Jeremy E Grenemyer]

Ooh, I'm reading about this in my brand new copy of Cosmos by Carl Sagan.

Everybody stop talking so I can catch up and then contribute something worthwhile.