43 replies to this topic

[catfishyeah]

I see, but since it has a gravitational pull on everything then wouldn't what I said be true? (yea thanks for pointing out my mistake in system)

[bison]

We don't know that life came into being only once on this planet, or that it could only do so during a short window of opportunity. It is considered entirely possible that life existed as long ago as 4.5  billion years, was totally destroyed in the Late Heavy Bombardment at 3.9 billion years ago, and began again from scratch, perhaps as late as 3.5 billion years ago. This raises the possibility of a rather broad 'window' of up to a billion years, during which life conceivably formed, and very possibly did so repeatedly, and under a variety of conditions. Of course these are possibilities, not certainties, which is all that can be reliably said about such remote times.

[psyche101]

bison, on 13 December 2011 - 02:56 AM, said:

We don't know that life came into being only once on this planet, or that it could only do so during a short window of opportunity. It is considered entirely possible that life existed as long ago as 4.5  billion years, was totally destroyed in the Late Heavy Bombardment at 3.9 billion years ago, and began again from scratch, perhaps as late as 3.5 billion years ago. This raises the possibility of a rather broad 'window' of up to a billion years, during which life conceivably formed, and very possibly did so repeatedly, and under a variety of conditions. Of course these are possibilities, not certainties, which is all that can be reliably said about such remote times.

The fossil record does not agree, it shows life as just beginning 3.5 to 4 billion years ago. The only forms of life that date back 4 billion years are procaryotic cells.

[lost_shaman]

scowl, on 12 December 2011 - 05:07 PM, said:

No, it's 100% supported. Early life formed in conditions that are considered inhabitable to us, therefore the pleasant conditions we enjoy on Earth today are not the conditions that form life.

I know I've said that same thing.

scowl, on 12 December 2011 - 05:07 PM, said:

Yes, we don't know a lot of things but we do know every point that I made. We know that the conditions on Earth have changed dramatically in the three billion years since life was created on it and no other forms of life have been created and survived (except parasitic viruses). The formation of life seems to have happened very quickly under extremely fortunate conditions that only existed briefly. That was followed by even more extremely fortunate conditions that didn't destroy that life and allowed it to evolve to survive further climatic changes.

Look, I think you are making some strange statements. We know life evolved after it formed. What is your point? 30,000 years ago Homo Erectus, Neanderthals, and Homo Sapiens all three inhabited the Earth. Note this is about 40,000 years after Toba which is considered the major stressor of Homo Sapiens.

scowl, on 12 December 2011 - 05:07 PM, said:

Yes, on Earth. We really don't know what early life was and we don't know how close it was to being destroyed. It's possible that most life in the universe never advances beyond primitive stages before it's wiped out forever. We know that Earth was an extremely lucky set of unlikely circumstances.

For some reason many people think that every planet that might have something close to Earth conditions has just gotta have life on it because it would be like so cool! When you look at the history of the Earth, you really appreciate how improbable life is.

I disagree with you. Life formed early and Thrived not simply survived. It transformed the planet into what we know today. i.e. a comfortable planet.

[bison]

psyche101, on 13 December 2011 - 03:02 AM, said:

The fossil record does not agree, it shows life as just beginning 3.5 to 4 billion years ago. The only forms of life that date back 4 billion years are procaryotic cells.

The known fossil record is scarcely the last word here. Is it probable that we have just happened to find the remains of the very oldest life on Earth?  Can we even be certain that the earliest life left fossils that still exist today? Even if the date is 4 billion years, this is early enough to have been completely destroyed in the Late Heavy Bombardment, ~ 100 million years later. If so, life would have had to start again, under different conditions than before, and probably several hundred million years after its original inception.

Edited by bison, 13 December 2011 - 05:00 PM.

[scowl]

lost_shaman, on 13 December 2011 - 07:11 AM, said:

Look, I think you are making some strange statements. We know life evolved after it formed. What is your point?

At some point life was able to not just expand but evolve. Evolution and diversity are two requirements for the long-term survival of life. Strange statement? Maybe if you haven't heard it before.

Quote

I disagree with you. Life formed early and Thrived not simply survived. It transformed the planet into what we know today. i.e. a comfortable planet.

I can't find any evidence that it thrived (why did you capitalize that?). We don't know how long it took before it covered the planet or when it started to evolve. The evolution is what prevented it from being destroyed the planet started to change. It's possible that life on other planets was no so lucky and altered conditions to where it killed itself.

The point is that there are a lot of variables that worked out for life on Earth. Any one of those could have prevented it or wiped it out before high forms could evolve.

[psyche101]

bison, on 13 December 2011 - 04:59 PM, said:

The known fossil record is scarcely the last word here.

I disagree. It shows us the development of life, as well as the progression life took.

bison, on 13 December 2011 - 04:59 PM, said:

Is it probable that we have just happened to find the remains of the very oldest life on Earth?  

Well, yes, we have seen the remains of the oldest life on earth, and it is microbial. And with the model of life that we have today, that progression makes perfect sense.

bison, on 13 December 2011 - 04:59 PM, said:

Can we even be certain that the earliest life left fossils that still exist today?

Yes, we have a record of them, and the transitions made to the many complex forms we see today.

bison, on 13 December 2011 - 04:59 PM, said:

Even if the date is 4 billion years, this is early enough to have been completely destroyed in the Late Heavy Bombardment, ~ 100 million years later. If so, life would have had to start again, under different conditions than before, and probably several hundred million years after its original inception.

Very different conditions, earth had no atmosphere. It has been replaced three times. The first atmosphere was primarily H & He, which was blasted away before the planet established magnetic fields. Once they were established, the atmosphere filled with sulfurous, nitrogenous and carbon compounds. This is when life began to take hold, and anaerobic organisms stared to produce oxygen, which was the catalyst for life, even though it was a poisonous byproduct to any life at the time. Are you taking into account coalescence, the formation of the moon, the formation of the atmosphere, and the cool down period after that? How much time does that leave you to sterilize earth, and then start all over again, without a trace of previous forms after all that has taken place?

This is what the world is proposed to have looked like during heavy bombardment




Do you have any reason to believe life sprung forth during this turbulent period?

Edited by psyche101, 13 December 2011 - 10:28 PM.

[scowl]

bison, on 13 December 2011 - 02:56 AM, said:

We don't know that life came into being only once on this planet, or that it could only do so during a short window of opportunity.

That's true. We only know that we haven't found any traces of this other life but the odds of that are extremely small in any case.

Quote

It is considered entirely possible that life existed as long ago as 4.5  billion years, was totally destroyed in the Late Heavy Bombardment at 3.9 billion years ago, and began again from scratch, perhaps as late as 3.5 billion years ago. This raises the possibility of a rather broad 'window' of up to a billion years, during which life conceivably formed, and very possibly did so repeatedly, and under a variety of conditions.

That is certainly possible, but then you have to ask, "Why were these ancient conditions prime for the repeated formation of life but the four billion years after it were not?" I think that holds the key to the formation of life (on any planet) but we don't know what it is.

Quote

Of course these are possibilities, not certainties, which is all that can be reliably said about such remote times.

Yes, they're not even probabilities. We know so very little about the formation of life on Earth that it's hard to speculate how it would happen on other planets.

[psyche101]

lost_shaman, on 13 December 2011 - 07:11 AM, said:

I disagree with you. Life formed early and Thrived not simply survived. It transformed the planet into what we know today. i.e. a comfortable planet.

I suspect in these early years there was still quite some bombardment, it strikes me that once life took hold, it would be hard to end life as billions and billions of tiny organisms. We know all water bodies on early earth were loaded with Coacervates, so you would have to near destroy the planet, or at least everything on it to wipe life out once it takes hold. It would be easy to destroy one big thing, but much harder to destroy billions of tiny things.

[lost_shaman]

bison, on 13 December 2011 - 04:59 PM, said:

The known fossil record is scarcely the last word here. Is it probable that we have just happened to find the remains of the very oldest life on Earth?  Can we even be certain that the earliest life left fossils that still exist today? Even if the date is 4 billion years, this is early enough to have been completely destroyed in the Late Heavy Bombardment, ~ 100 million years later. If so, life would have had to start again, under different conditions than before, and probably several hundred million years after its original inception.

Genetic evidence suggests life was present by 4.29 Ga, therefore life on Earth survived the Late Heavy Bombardment.

http://www.evolbiol....es/sheridan.pdf

[psyche101]

lost_shaman, on 13 December 2011 - 10:40 PM, said:

Genetic evidence suggests life was present by 4.29 Ga, therefore life on Earth survived the Late Heavy Bombardment.

http://www.evolbiol....es/sheridan.pdf

Top link mate

We propose a date of 4.29 Ga for the Last Common Ancestor of the Bacterial and Archaeal Domains and a date of 3.46 Ga for the Bacterial and Archaeal Domain individual radiations. These divergence times do not conflict with geological evidence but call into question the interpretation of early Archean (»3.5 Ga) microfossils as evidence of cyanobacterial lineages

Dated 2003! I Must keep up, I had only heard about the 4 billion threshold about 6 months ago I was still looking for a link. Thanks for that

Edited by psyche101, 13 December 2011 - 10:51 PM.

[bison]

Interesting article. It suggests the possibility that forms of life arose completely independently of ours, and persist to this day. Since most organisms remain genetically uncharacterized, we can scarcely rule this out. We wouldn't know if, or when they began.  http://www.guardian.co.uk/science/2009/feb/15/microbes-earth-tree-of-life

Edited by bison, 14 December 2011 - 12:39 AM.

[psyche101]

bison, on 14 December 2011 - 12:39 AM, said:

Interesting article. It suggests the possibility that forms of life arose completely independently of ours, and persist to this day. Since most organisms remain genetically uncharacterized, we can scarcely rule this out. We wouldn't know if, or when they began.  http://www.guardian.co.uk/science/2009/feb/15/microbes-earth-tree-of-life

Is there any traces of anything that give rise to such reasoning? Or is it pie in the sky stuff?

[psyche101]

bison, on 14 December 2011 - 12:39 AM, said:

Interesting article. It suggests the possibility that forms of life arose completely independently of ours, and persist to this day. Since most organisms remain genetically uncharacterized, we can scarcely rule this out. We wouldn't know if, or when they began.  http://www.guardian.co.uk/science/2009/feb/15/microbes-earth-tree-of-life

It sort of reminds me of the ideal of life on Europa. Even if we find life there, is it Alien? Not really if it carries the same signatures that life on earth does. We might have seeded life through panspermia. Even should we find life on another planet, there are still real hurdles to overcome before it can be considered as truly Alien.