Earth is Probably Unique

[laklak]

Nobody will remember Microsoft in the new iUniverse.

[mistermack]

Now, to be fair, it has been suggested that it is possible that life could have originated many times on the early Earth, but only one start-up was successful, and drove the other, different biochemistries to extinction by resource competition. One would not expect to easily discover evidence for such failed biochemistries.

That's what I thought, immediately, when I first heard it claimed that life only evolved once on the planet. How could they know that? It could have evolved lots of times, and just got eaten, or driven to extinction, by the life that was already there.
But I've only ever heard the "life evolved once" claim on the various documentaries I've seen on the origin of life.

I've not seen or read to the contrary, but I doubt it myself. But maybe they have their reasons.

Of course, we don't know that life originated even ONCE on Earth.
It could have happened on Mars, and got transferred on a chunk of Mars rock that travelled to Earth. That's why they are looking so hard for signs of life on Mars.
Since Mars had oceans, billions of years ago, you would expect life to have bump-started there too, if it was a likely occurrence.

The signs so far are that there wasn't any life there. But that could easily change.

[JimC]

Now, to be fair, it has been suggested that it is possible that life could have originated many times on the early Earth, but only one start-up was successful, and drove the other, different biochemistries to extinction by resource competition. One would not expect to easily discover evidence for such failed biochemistries.

That's what I thought, immediately, when I first heard it claimed that life only evolved once on the planet. How could they know that? It could have evolved lots of times, and just got eaten, or driven to extinction, by the life that was already there.
But I've only ever heard the "life evolved once" claim on the various documentaries I've seen on the origin of life.

I've not seen or read to the contrary, but I doubt it myself. But maybe they have their reasons.

Of course, we don't know that life originated even ONCE on Earth.
It could have happened on Mars, and got transferred on a chunk of Mars rock that travelled to Earth. That's why they are looking so hard for signs of life on Mars.
Since Mars had oceans, billions of years ago, you would expect life to have bump-started there too, if it was a likely occurrence.

The signs so far are that there wasn't any life there. But that could easily change.

The real point is not whether life evolved only once, or whether there were several failed start-ups we will never know about, but the indisputable fact that the current tree of life on Earth had a single starting point, and that the underlying but somewhat arbitrary biochemistry of that founding event underlies all life on Earth at the present.

[Rum]

I thought there had been some recent discussion about the possibility that life might have started independently of our particular evolutionary tree at deep underwater volcanic plumes and the like.

[rainbow]

I'm not here to do your thinking for you.
Think of monkeys and typewriters.

I do.

Yet you think that an exceedingly rare event such as the origin of life would follow the exact same sequence even on a different planet.

Did you forget to put on your thinking hat?

I think it's you that needs a new hat.
Rare events are usually rare, because there are very few ways they can happen.

Rubbish. A particular sequence on a roulette wheel is rare, but there are many possible sequences.

If there were millions of ways for something to happen, it's not likely to be rare.

And on Earth, life only happened once, in 4.5 billion years, according to the geneticists.
That's mega rare. And that doesn't point to lots of ways it can happen.

So here is how it works.

Your monkeys type away and eventually they replicate a line out of the entire works of of Shakespeare.

Give them more time. Do you believe that they will next type out the same line, or a different one from the Collected Works?

[rainbow]

Now, to be fair, it has been suggested that it is possible that life could have originated many times on the early Earth, but only one start-up was successful, and drove the other, different biochemistries to extinction by resource competition. One would not expect to easily discover evidence for such failed biochemistries.

Yet different life forms exist in the same environment. Parrots exist in the jungle but so do snakes, trees, bugs, fungi, etc.
Why can't different biochemistries coexist?

[JimC]

Now, to be fair, it has been suggested that it is possible that life could have originated many times on the early Earth, but only one start-up was successful, and drove the other, different biochemistries to extinction by resource competition. One would not expect to easily discover evidence for such failed biochemistries.

Yet different life forms exist in the same environment. Parrots exist in the jungle but so do snakes, trees, bugs, fungi, etc.
Why can't different biochemistries coexist?

I'm not certain whether there would be automatic competitive displacement or not, although in the simplified pre-biotic world, there would not exist the complex niche differentiation of today's biome. I suspect, therefore, there would be only one winner.

In fact, of course, there is only one winner, from which we are all descended. The question of whether there once were others, or whether the existing biochemistry was a once-off remains an unknown, as does the possibility (remote I suspect) that if the tape of life on Earth were to be played again, we might see two or more clearly distinct biochemistries co-existing.

[mistermack]

I think it's you that needs a new hat.
Rare events are usually rare, because there are very few ways they can happen.

Rubbish. A particular sequence on a roulette wheel is rare, but there are many possible sequences.

Yes, there's only one way a particular sequence can happen. Among millions of other possible sequences.
That matches what I said. Why does that make it rubbish, in your judgement?

[Brian Peacock]

I'm not here to do your thinking for you.
Think of monkeys and typewriters.

I do.

Yet you think that an exceedingly rare event such as the origin of life would follow the exact same sequence even on a different planet.

Did you forget to put on your thinking hat?

I think it's you that needs a new hat.
Rare events are usually rare, because there are very few ways they can happen.
If there were millions of ways for something to happen, it's not likely to be rare.

And on Earth, life only happened once, in 4.5 billion years, according to the geneticists.
That's mega rare. And that doesn't point to lots of ways it can happen.

I'm trying to keep it simple.

In an stahgeringly massive universe like ours even the most rarest of things, like a viable biosphere, might be relatively abundant - numerically speaking.

[pErvinalia]

Now, to be fair, it has been suggested that it is possible that life could have originated many times on the early Earth, but only one start-up was successful, and drove the other, different biochemistries to extinction by resource competition. One would not expect to easily discover evidence for such failed biochemistries.

Yet different life forms exist in the same environment. Parrots exist in the jungle but so do snakes, trees, bugs, fungi, etc.
Why can't different biochemistries coexist?

I'm not certain whether there would be automatic competitive displacement or not, although in the simplified pre-biotic world, there would not exist the complex niche differentiation of today's biome. I suspect, therefore, there would be only one winner.

Yeah, that would be my explanation as well.

[mistermack]

The essential thing about life, is the ability to reproduce and evolve.
For a complicated being to evolve from basic molecules or energy systems, it seems likely that reproduction is essential. And not perfect reproduction, because there would be no evolution. And not hugely IMPERFECT reproduction, because that wouldn't be reproduction.

You need something that reproduces, almost perfectly, with just the very rarest of errors.

Scientists have been trying to achieve that kind of thing in the lab, with no success.
So other kinds of life seem no easier to start up, than our kind.

The thing about the universe is that it might seem infinitely varied, with the vast numbers of stars and planets. But actually, it's surprisingly uniform, as all matter is composed of the same basic elements of the periodic table. And all of the solid bodies came about in the same way, from gas clouds of hydrogen and helium forming stars, exploding as supernovas, producing some of the heavier elements.

So even if the quantity of ingredients is near infinite, the number and nature of the available ingredients is limited, and likely to be very similar. And similar ingredients will probably make similar cakes.

So if we can't make a different kind of life here on Earth, it might be just as unlikely everywhere else.

I've often mused about the chances of reproduction involving massless particles, travelling at the speed of light. What if they could get together in some way, and reproduce, like our organic particles do?
You could have evolution happening at the speed of light. All of our development, that's taken nearly five billion years of evolution, could happen in a month.
You could go from mindless particles to super-intelligent aliens, in between your monthly pay-cheques.

[JimC]

mistermack wrote:

So even if the quantity of ingredients is near infinite, the number and nature of the available ingredients is limited, and likely to be very similar. And similar ingredients will probably make similar cakes.

At the level of elements, yes. At the level of potential organic building blocks, no. Even if we are talking water based, with carbon molecules containing some nitrogen and phosphorus, the potential number of small to medium sized building block molecules is very large. We have settled, quite arbitrarily, on the building blocks that appeared very, very early. Having locked that in, no more were needed. A different planet may well have amino acid analogues, perhaps even with a little overlap to ours, but the chance of it having exactly the same set is very, very low...

[mistermack]

mistermack wrote:

So even if the quantity of ingredients is near infinite, the number and nature of the available ingredients is limited, and likely to be very similar. And similar ingredients will probably make similar cakes.

At the level of elements, yes. At the level of potential organic building blocks, no. Even if we are talking water based, with carbon molecules containing some nitrogen and phosphorus, the potential number of small to medium sized building block molecules is very large. We have settled, quite arbitrarily, on the building blocks that appeared very, very early. Having locked that in, no more were needed. A different planet may well have amino acid analogues, perhaps even with a little overlap to ours, but the chance of it having exactly the same set is very, very low...

That could be right. But the closer a life form was to ours, the easier it would be for our bacteria to attack. But of course, it could work the other way too.
Aliens could bring stuff like their own bacteria that could decimate life on Earth.

I wonder what would happen, if humans, in a thousand years time, discovered an Earth-like planet with similar looking life on it?
You couldn't just blunder in, like in the movies, or you might be dead within days, from infections that you had no immunity to. But then the Earth bacteria from your own rotting corpse might colonise the whole planet and destroy what's there.
Perhaps they could send down some clones of Donald Trump, as guinea pigs, to see if they survive.
He could prove useful after all.

[rainbow]

I think it's you that needs a new hat.
Rare events are usually rare, because there are very few ways they can happen.

Rubbish. A particular sequence on a roulette wheel is rare, but there are many possible sequences.

Yes, there's only one way a particular sequence can happen. Among millions of other possible sequences.
That matches what I said.

Only if you can show that there is only one possible sequence of events that might lead to the formation of life.

Please proceed.

[rainbow]

mistermack wrote:

So even if the quantity of ingredients is near infinite, the number and nature of the available ingredients is limited, and likely to be very similar. And similar ingredients will probably make similar cakes.

At the level of elements, yes. At the level of potential organic building blocks, no. Even if we are talking water based, with carbon molecules containing some nitrogen and phosphorus, the potential number of small to medium sized building block molecules is very large. We have settled, quite arbitrarily, on the building blocks that appeared very, very early. Having locked that in, no more were needed. A different planet may well have amino acid analogues, perhaps even with a little overlap to ours, but the chance of it having exactly the same set is very, very low...

Correct.