What Determines the Differences in Life Across Different Planets?

[awestruck]

Newbie...first post...apologies in advance.

How soon after the big bang could intelligent, technological life evolve?

 

[jackmell]

Newbie...first post...apologies in advance.

How soon after the big bang could intelligent, technological life evolve?

Gotta' reference: "The World Within The World" by John Barrow. It's a great book in my opinion. Tons of stuff:

Quote:

"most biochemists believe that the element carbon, . . . , is the only viable foundation from which chemical life can arise spontaneously.

"At least 10 billion years of stellar burning are required to produce essential elements like carbon"

Didnt' stars begin to form shortly after the Big Bang? Think so. Then keep in mind life appeared on the Earth very soon after it cooled to a decent temperature, and then another 4 billion years to evolve man and if we take that as about average which I don't think is unreasonable, then on the order of about 14 billion years I would think and since the visible Universe is about 13 billion light years (maybe 16? another not sure) and expanding, that gives credence for the fact the Universe is so large: a smaller one would not have had time to evolve intelligent life to ponder the question.

 

[Freeman Dyson]

Gotta' reference: "The World Within The World" by John Barrow. It's a great book in my opinion. Tons of stuff:

Quote:

"most biochemists believe that the element carbon, . . . , is the only viable foundation from which chemical life can arise spontaneously.

"At least 10 billion years of stellar burning are required to produce essential elements like carbon"

Didnt' stars begin to form shortly after the Big Bang? Think so. Then keep in mind life appeared on the Earth very soon after it cooled to a decent temperature, and then another 4 billion years to evolve man and if we take that as about average which I don't think is unreasonable, then on the order of about 14 billion years I would think and since the visible Universe is about 13 billion light years (maybe 16? another not sure) and expanding, that gives credence for the fact the Universe is so large: a smaller one would not have had time to evolve intelligent life to ponder the question.

Ya, I've read Barrow and seen him bring up that point many times. It takes a lot of time and space for the universe to support a single outpost of life. I'm not sure we can use life here as an average though. Who knows what other forms life could take. I agree that we have to at least wait for the first stars to release heavier elements but it is hard to estimate life and evolution on other worlds. We only have one point of reference. Unlike most other things in astronomy which we can compare.

 

[awestruck]

Thanks for the responses, interesting. I hadn't heard of John Barrow, I'll check his book out.

 

[Nabeshin]

"At least 10 billion years of stellar burning are required to produce essential elements like carbon"

This seems very wrong. First generation stars, which were extremely massive and went through their lifetimes quickly, would fuse all elements up to iron and beyond when they go supernova at the end of their lifetime. I think the first stars are hypothesized to have formed a few hundred million years after the BB, so any second generation star formed after these supernova has a fighting chance of forming a metallic protoplanetary disk for planets and hence life.

However... Since massive stars don't convect, it's possible that they simply don't produce enough of the heavy elements to make a difference. It might just be a question of scale, but there certainly would be some carbon well before 1Gyr.

 

[TimBowe]

Gould expressed the opinion that intelligence may have been an improbable event because are evolution consists of a staggeringly improbable series of events, and anyone of these events could have occurred differently. Many of us are tempted to see the present biota of the Earth as in some way necessary but the reality is that humans may be an improbable end point on the evolutionary tree. We are only here because of a staggeringly improbable series of events that just so happened to occur in precisely the required sequence.

Even if we were to start a million times again, it still is improbable that beings like humans would emerge again. Gould takes his point of departure in the beginning of the cambium, a geological period when life had already become multicellular. In a particular formation of rocks in Canada, the Burgess Shale, fossils from this period, some 530 million years ago, have been found. Among them Gould claims to discern twenty-five different forms of life, each of which could have resulted in a particular kind of animals, such as the insects or the vertebrates. Only four of those twenty-five still have descendants. If some others had survived, life would be quite different now.

Darwinian selection is utterly blind, there is no directionality in evolution, no progress, no ladder, merely a random walk through possibilities.

"Alter any early event, ever so slightly and without apparent importance at the time, and evolution cascades into a radically different channel"

Stephen Jay Gould

Even if conditions were right there is no way to know how frequently life would evolve or what portion of living creatures would develop intelligence. Experts on evolution such as Gould viewed the evolution of human beings as exceedingly improbable "the accidental result of an enormous concatenation of improbabilities."

 

[jackmell]

Nice points you guys make. I guess the 10 billion years does seem a bit long to me but I suspect Barrow would have an explanation for that figure. Regarding Gould, I got the phrase "massively contingent" from him and have used it often in other discussions about life. Lately though I'm starting to think the evolution of life in the Universe may not be so different as what we find on earth. For one thing, when we observe the heavens, we find in general, basically the same thing in any direction that we look: stars and galaxies with only variation about the same "body plan". Galaxies are "clusters" of stars more or less spherical in shape, and stars are basically also shaped the same and they all follow basically the same dynamics of motion and evolution with slight variation about those general plans such as retrograde orbits, barred and spiral. For example, every star in the Universe (most at least) follow Hertzsprung-Russell. Why then would we expect life to be so qualitatively different on other planets? Perhaps life too follows the same "body plans" with only variation about those general shapes. I'm starting to suspect it might.

I don't wish to challenge Gould. He was the expert and I'm not but I believe had he been both a Biologist and Mathematician, he might have had a different opinion about the evolution of life.

 

[Nabeshin]

Why then would we expect life to be so qualitatively different on other planets?

Many reasons. One could imagine life based on an element other than carbon, for example silicon. Also, all life on Earth shares the basic DNA structure. I imagine that to reproduce this exact molecule elsewhere would be a fat chance indeed! Anything based on some fundamental molecule other than DNA is bound to be very different. These are two big ones I can think of, and then there are tons of smaller ones like planet composition, host star radiation, surface gravity, etc. that come together to make (even carbon, DNA based) life probably look significantly different on other worlds.

All just idle speculation, though. I don't think anyone can give informed answers on these topics.