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 Jadenim wrote:
True, absence of evidence isn’t evidence of absence, but given the speed and extent at which multi-cellular life proliferated once it got going, it’s unlikely that there’d be no evidence if it had happened before.

Except how much there would be left after say 300 million years? How much of humans are left after that? Ground has changed, things been buried, things we created gone away.

There is a great book "The World Without Us" that goes through that particular thought experiment.

Our mighty works are unlikely to last that long, with apparently the Channel Tunnel being an unlikely winner as is may continue to be relatively identifiable as a non-natural object after a few million years

tneva82 wrote:

 Jadenim wrote:
True, absence of evidence isn’t evidence of absence, but given the speed and extent at which multi-cellular life proliferated once it got going, it’s unlikely that there’d be no evidence if it had happened before.

Except how much there would be left after say 300 million years? How much of humans are left after that? Ground has changed, things been buried, things we created gone away.

We have evidence of single cell life covering the ~2-billion years up until the emergence of multi-cellular life (and another billion or so until it really gets going); now admittedly it's pretty sparse samples, but that's an awful lot of time for something to have been preserved, if multi-cellular life had occured significantly earlier than our current understanding. Now I wouldn't be surprised if we push back the date a few hundred million years as we find more fossils, but I doubt you're going to be knocking it back substantially closer to the emergence of life.

Similarly, we've already found that the Cambrian "explosion", was more of a "fairly rapid expansion" (i.e. a whoomph, rather than a boom), as a lot of species now also start to appear in Edicarian and I expect we'll continue to flatten that curve into the past.

The really fun one is if we'll ever find any evidence of previous technological species; our current avian dinosaurs are pretty smart and possess a number of tool using species and language potential, so I think there's a non-zero chance that one of the extinct dinosaur species developed at least a stone-age level of technology (i.e. use of fire and stone tools). Again, various human species existed at that technological level (including homo sapiens, with our current intelligence) for hundreds of thousands of years before we really took off in the last 12,000 with the development of agriculture.

tneva82 wrote:

 Jadenim wrote:
True, absence of evidence isn’t evidence of absence, but given the speed and extent at which multi-cellular life proliferated once it got going, it’s unlikely that there’d be no evidence if it had happened before.

Except how much there would be left after say 300 million years? How much of humans are left after that? Ground has changed, things been buried, things we created gone away.

In terms of fossil evidence of complex life - especially if there are hard parts like skeletons, carapaces or shells - there would be a LOT of evidence.

We do have fossil evidence of structures called stromatolites going back billions of years. They were made by bacteria and they still exist in places.

Not to mention that fossil evidence isn't the only kind of evidence we have - IIRC ground-penetrating radar has been used to uncover the foundations of older structures (though that's more on the order of thousands rather than millions of years), and there's always major landscaping projects like dams and canals and whatnot alongside them. I'm no expert, but I'd imagine that unusual patterns of compaction/erosion could point to our existence some time after the structures that made them have decayed away.

 waefre_1 wrote:
Not to mention that fossil evidence isn't the only kind of evidence we have - IIRC ground-penetrating radar has been used to uncover the foundations of older structures (though that's more on the order of thousands rather than millions of years), and there's always major landscaping projects like dams and canals and whatnot alongside them. I'm no expert, but I'd imagine that unusual patterns of compaction/erosion could point to our existence some time after the structures that made them have decayed away.

Erosion is a thing. And not just that, each ice age scrapes soil down to bedrock, to the point last one completely removed tens of thousands of years of archeological evidence of human habitation from nothern Europe, north America, and Russia. Even in areas where that wasn't a problem, like Anatolia and Levant, very little of early human construction survived due to warfare, later cultures recycling stones from earlier buildings for new ones, and weather grinding rocks to dust.

And that's where cultures were advanced enough to use stone, in what is now Poland we have very little evidence of any old city or village due to them built from abundant wood save for famous Biskupin town that only survived due to sinking into marsh (and even so so little archeological evidence survived there scientists for a long time couldn't even agree what culture exactly built despite pretty good tool and pottery descriptions from other sites - doubly so because there is often no agreement what peoples belonged to what 'culture', archeologically speaking):

https://en.wikipedia.org/wiki/Biskupin

This is site pretty close to one of the biggest cities in Poland, huge for the time period and not that old (late 700s) - yet despite that it was only discovered in 1930s. If something so significant can remain hidden for so long, I have little hope for older and more obscure sities, especially ones that were located in good spots where humans still live as millennia of construction, digs, and land reshaping would obliterate old traces pretty fast.

Amazing pics of Jupiter

James Webb: Space telescope reveals 'incredible' Jupiter views https://www.bbc.co.uk/news/science-environment-62641866

And Artemis has a test run on Monday. Very exciting

In the much happier international news about rockets, Artemis has successfully launched. 6 days to the moon this time apparently. Gonna be awesome, even just to get updated photos of the dark side.

 Flinty wrote:
In the much happier international news about rockets, Artemis has successfully launched. 6 days to the moon this time apparently. Gonna be awesome, even just to get updated photos of the dark side.

I was a little worried when they had to send the red team back to the pad, then a little annoyed when I had to stay up an extra 45 minutes but when it left the pad and turned night into day it was awe inspiring. and then the sound wave hit.....