Francevillian biota - evidence for *ancient* multicellular life.

On Thursday, January 21st, 2016 at 2:27 am, Nitrocosm said:

As I said, it would much more conveniently, and plausibly, explain the long aeon of Earth's prehistory during which seemingly "nothing" happens.

Well, birds are technically dinosaurs: they are descended from a very specific group of dinosaurs (which were all feathered). Crocodiles on the other hand are the closest living relatives of dinosaurs (including birds).

It makes me wonder what else we were wrong about all this time. Feathered dinosaurs is a pretty big leap from what I saw in the textbooks...

Not a geologist so perhaps this is a stupid question but is it possible that some of the fossil record was lost to the Earth's mantle via tectonic subduction? The thought had just crossed my mind.

What are the chances that humans (or a species similar to us) evolved prior to some total devastating cataclysm in distant prehistoric times? The Earth's old enough to allow room for that, I think. The wrench in the theory would be that there's no traces of advanced civilizations but if was something that would have destroyed everything, is there a chance?

On Friday, January 22nd, 2016 at 5:08 pm, Nitrocosm said:

That is not a stupid question at all. As a matter of fact, that certainly has happened. Every few million years or so, the oceanic crust (the seafloor below the deep ocean basins - as opposed to the shelf areas which are geologically speaking part of the continents) gets completely recylced. The oldest seafloors that we have are generally from the early Jurassic, and if you go to the mid-oceanic ridges, fresh new oceanic crust is produced there today. In contrast to this we have several billion year old 'nuclei' of continental crust in various parts of the world. We also do see remains of former seafloor accreted into mountains. But there's likely a lot that was lost into the mantle, is covered below the sea level (the above mentioned shelf areas), or covered below glaciers (especially Greenland and Antarctica). Also with time, mountains of course get eroded and their remains forms the source material for newer, younger sediments.

On Monday, January 25th, 2016 at 9:07 pm, Stratus said:

Multiple devastating cataclysms have happened in Earth's history for sure, and the extinction of the dinosaurs wasn't the last one of them, nor the biggest. In my opinion, if there had been a more advanced (read: technological) civilization on Earth at some point in the distant past, we would see that and we would know that by now. I'm simply basing that on the fact that humanity's industrial civilization is making such a tremendous, and clearly visible impact on the planet. If we're leaving aside that, and look at pre-industrial human societies, there's some room for possibilities. Especially if you consider that at the height of the ice ages, the sea level was substantially lower, and some of the areas that were exposed and certainly had both wildlife and human inhabitation during the ice ages are now submerged below tens of meters of ocean. A good example is the Doggerland which occupied what is today the North Sea (between Britain, the Low Countries, Germany and Scandinavia), the Sunda Shelf in Southeast Asia, and the Sahul Shelf between Australia and New Guinea. In my humble opinion, its actually rather likely that we do not know the full story about prehistoric human societies (which no doubt existed at exactly these places during the ice ages, I should add). Wether these were more advanced societies than hunter-gatherers, I'd be sceptical.

I take it that the probability of humans evolving from scratch (all the way up from single-celled organisms) more than once in Earth's history is extremely unlikely, then.