We have DNA evidence that seems to point to the origins of modern humans to be in Africa. Is there any thinking about where on the planet life first arose?
The ocean.
We don’t even know how. Or if.
The origin of life is so ancient - before 3.6 to 3.8 billion years ago, the date of the earliest fossil evidence - that we have no possible way of knowing in what geographical area it might have arisen. In any case, the continents are of vastly different size, configuration and position now than they were then, and any of the ocean floor that existed then is long gone.
Some of the most ancient branches of life, groups of the Archaea, are extreme thermophiles, capable of surviving at extremely high temperatures. For this reason, some scientists have postulated that life originated at deep-sea hydrothermal vents, but this is essentially speculation.
The entire crust gets recycled every few billion years, so there’s no meaningful way to make this an answerable question.
There are lots of plausable theories for abiogenesis, but it seems unlikely we’ll ever know how and where life got started.
To summarize abiogenesis, essentially the idea is that you have a set of molecules that keep building up and becoming more complex until – eventually – they become life. Ideally, for that to happen you need an environment that has enough chemical reactions to provide sufficient variation without being so completely tempestuous that any complex molecule that is formed is quickly broken back down. But that’s simply a recipe for the environment that’s most likely to produce sufficiently complex structures. And even then, it may still take billions of years to get the perfect happenstance of reactions to create life, if ever.
There’s also the issue that some materials probably have qualities more conducive to creating a life form. So you don’t just need random chemical reactions, you need the presence of the sorts of atoms and molecules that would be ideal to be in those reactions.
Of course, it’s entirely possible that we aren’t made out of the ideal materials (even for Earth’s environment), but for the purposes of tracking back our heritage, if we look at the makeup of the oldest creatures and where the materials they are made up from are often part and parcel of various chemical reactions, and if we know the right tempestuousness of reactions that is ideal to the creation of life, we can infer the most likely origin. Where the actual point of genesis was would likely remain a mystery – we would just know the general sort of environment it would most likely have occurred in.
Potentially we can’t know what the ideal tempestuousness is, though. There’s no way to test it beyond setting up some test environments and waiting to see what happens. If it’s truly something where even with the ideal situation it might take billions of years to happen once…well, that’s not a science project you’re going to be around to see the result of.
There are people trying to replicate abiogenesis, mind, but I believe that their studies are more on the level of creating specific, potential predecessors of life and seeing if they have properties that could likely lead to forming into more complex creatures. If the steps to create those predecessors rely on simple chemistry and one can reasonably assert that such chemistry happens in nature on the random occasion, then even though you’ve used non-random reactions to create the creature, it still proves that abiogenesis is theoretically possible and, again, shows what situations would be ideal for creating life.
There’s a few major types of evidence that tell us when and where early humans came from. Most significant is the fossil record – we find bones in a particular region, and we can date those bones and other material buried in the same layer. For human evolution, there are enough good data points to tell us quite a bit.
Unfortunately, the earliest life forms are probably something very much like bacteria, and wouldn’t fossilize well. The best unambiguous fossils of early bacterial life are stromalites – a particular type of rocky formation created by layers of growing bacteria. They’ve been found in rock formations that date back 2 billion years. There are some other potential fossils from 3.5 billion years ago, but it’s hard to say if those are really microfossils of bacteria or just bacteria-shaped minerals created by geological processes.
And as other posters have mentioned, there aren’t many rock formations that have lasted that long, so even if there were more fossils formed billions of years ago the vast majority are lost to us.
DNA evidence can provide more detailed information about populations and migrations. For example, it can tell us when two geographically isolated groups shared a common ancestor, and this has helped our understanding of human origins and migration. But it’s not very useful on its own – good molecular clock data is calibrated against the fossil record and known rates of mutation. That’s something we can do with extant or recently extinct species, but we really can’t use DNA to get a decent estimate of the origin of life.
I always rather liked the (fictional(?)) idea Kurt Vonnegut put forth in The Sirens Of Titan, that there is something called a Universal Will To Become (UWTB) that is responsible for the very existence of a material Universe in the first place, and that makes life, or “systematic temporary local reversals of entropy”, happen.
Even this isn’t an open-and-shut case. In Guns, Germs, and Steel the author mentions the theory that humans may have evolved simultaneously in several parts of the world - for example there is evidence from fossils in China from over 100,000 years ago (prior to the supposed African genesis) that bear resemblance to modern Chinese. It’s still officially unresolved.
Just a nit, carry on.
Not entirely true. The continents have gradually accreted over a period of four billion years or so, so there are parts of them that have survived without being recycled for that long.
That’s called the Multiregional Hypothesis, and is an extreme minority view among paleoanthropologists. And I think you are mistaken about the Chinese fossils.
There is some recent genetic evidence that modern East Asian populations may have interbred to a small degree with extant, non-sapiens populations in Asia when modern humans first entered that region. But that is not the same thing as the Multiregional Hypothesis.
Life may not have originated on this planet. While there doesn’t seem to be confirmable evidence that there is an extraterrestrial source of life, it’s not impossible. The earliest evidence of life comes from the accumulation of single cell life form, which indicates life had been established much earlier.
The fossil record strongly points to humans arising in Africa, but the fossil record is limited, so conclusive proof may never be available. As far as I can tell, theories about modern humans developing outside of Africa are simply speculation.
It was really the genetic data that clinched things for the Out of Africa Hypothesis.
Negative (I know because I just read this recently). Page 40 of my cite:
It may very well be a minority view; I was just pointing out the African origin isn’t universally agreed-upon.
I don’t think that can be considered absolute proof, but a very high level of proof. For instance, pre-humans may have left Africa, developed into modern humans and returned. Genetic information may not be sufficient to detect that. But there isn’t any other evidence to support that either, it is simply speculation. And seems unlikely that they could have moved very far away and returned without leaving genetic or fossil evidence anyway.
I haven’t seen the book cited by Rigamarole, but if physical anthropology is the basis for that theory, it would be extremely weak without a more complete fossil record.
Jared Diamond isn’t an anthropologist. The interpretation of those fossils as having modern racial features is also an extreme minority view. Note how even Diamond has to say “if true”. I’m going by memory here, so I may be off by a few thousand years, but we don’t even see recognizably modern looking racial features in fossils of H. sapiens until about 20k years ago.
I don’t think it’s accurate to call this “unresolved” until every single living paleoanthropologist is convinced. In that case, the issue of Global Warming is “unresolved”. It’s about as resolved as it gets in this field.
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