TIL From the article “To determine the age of the tools, the researchers took advantage of the planet’s changing magnetic field.

From time to time, Earth’s magnetic field flips, turning north to south. Magnetic minerals in the soil and ocean are pushed into alignment with the field; when they are trapped in rocks, they still point in the telltale direction.

Geophysicists have precisely determined the timing of these magnetic flips, which have taken place at the same time all around the world. It’s a useful way to date the material found in layers of rock.”

These flips happen quickly on a geologic timescale but are not quick on a human timescale. It takes around 1-10 thousand years for the field to flip. The last one happened around 780k years ago. More often the magnetic field gets quite weak for awhile, like the field is going to flip, but then the magnetic field returns to the same strength and direction. These are called excursions and the last one of these was likely the Laschamp excursion about 40k years ago.

Huh, interesting. Do you know if anyone has looked at whether the rate of genetic mutations increases during those 10k year periods of weakened magnetic field? Seems like that would cause the magnetosphere to become less effective at deflecting cosmic radiation.

Many people have looked into if these reversals can cause extinction events and they don't appear to. Determining a change in average mutation rates seems like something that would not be possible from the rock record. The last reversal was so long ago that DNA does not survive well enough to do a good study even if one had the right kind of samples to work with.

Yeah, makes sense. I was thinking that you could look for an uptick in biodiversity or something from the fossil record, but I'm sure it would be tricky to separate the reasons for that.

Super interesting, thanks for posting about the Laschamp Event

Funfact: key evidence for the theory of tectonic plates was the changing magnetic field direction in rocks with distance from their magma source.

Always seemed like one fantastical theory being supported by another fantastical theory. (Don't worry, I'm not a tectonic skeptic.)

As I understand it there's a strong belief amongst Chinese nationalists that the Chinese diverged early from other humans. It makes me suspicious of this announcement, as it may be playing to those beliefs. However, I'm not sure it is untrue, doesn't bother me either way.

Well, to that end the very first sentence of this article is wrong. These weren't carved by ancestors of anyone living today. This was homo erectus, a distant cousin.

Well, many Chinese scholars claim the Chinese are descendants from Homo Erectus.

It's even shown on a BBC documentary, they get disappointed when DNA analysis disproves their skull-shape "evidence".

https://en.wikipedia.org/wiki/The_Incredible_Human_Journey#2...

The fact that I have healthy half-chinese kids puts the nail in the coffin of that idea... among many other things. It's about as serious an idea as a flat earth or "intelligent design".

I don't think even the strongest Chinese nationalist would claim that the Chinese diverged from everyone else 2 million years ago!

Actually there was a very significant amount of money ploughed into researching that exact topic in the PRC.

With significant and predictable sadness when the results didn't go their (the CCP and Chinese nationalists) way.

A google search gives a good paper on the topic:

https://core.ac.uk/download/pdf/28941533.pdf

TLDR: CCP, seeking to shore up ethno-nationalism (not an especially rare occurance in Chinese history) spent a LOT of time and research trying to prove that Han Chinese are in fact originally descended from Homo erectus Pekinensis rather than the African Homo Sapiens. (EDIT: Spelling)

Homo erectus pekinensis isn't 2 million years old.

Go back 2.1 million years, like these stone tools, and it's not even clear that there is a genus Homo.

what's wrong with trying to prove something? As long as it is research, I can see nothing wrong with it. Especially if they want to understand where they are from.

So, if we looked at all of the "oldest yet found" discoveries (that held up to later scrutiny), and plotted their date vs. the date they were found, would we see it asymptotically approaching some (presumably actual true) value? A job for an enterprising data scientist/archaeologist out there.

What would that show?

Perhaps, what the actual value could be expected to be. So, for example, you don't do a lot of work on top of the current estimates for oldest tool-using humans outside of Africa, that is likely to be overturned in ten or twenty years.

It wouldn't be convergent.

Interesting if true. I could easily believe what you say, but do we know that? I don't know the field well enough to say.

Yes it is rather trivially true. The age is getting exponentially further while discoveries are happening faster.

But that reflects improvements in technology, not anything about what’s being measured.

The original Nature article published July 11[1].

[1]https://www.nature.com/articles/s41586-018-0299-4

The 'out of africa' story gets more and more hard to sustain the longer people look around for other stories in the emergence of modern humans. Yes, the apes is out of africa. And then? it gets really complicated really fast.

Also, reminded of the endless jokes about who is more advanced from what archeologists find in their own country: Americans find copper wire: invented primitive networks. Russians find Glass threads: invented optical networks. Irish dig up a bog and find nothing: invented wifi!

“Out of Africa” refers to the theory that Homo sapiens (our direct ancestors) came out of Africa. This article is referring to tools made by Homo erectus or another homonid group. So, not our direct ancestors, more distant cousins.