About 120,000 years in the past, two or three folks walked alongside the shore of a shallow lake in what’s now northern Saudi Arabia. They left behind not less than seven footprints within the mud, and as we speak these tracks are the oldest identified proof of our species’ presence in Arabia.
A Pleistocene stroll by the lake
Think about that you simply’re a hunter-gatherer about 120,000 years in the past, and also you’re strolling out of jap Africa into Eurasia. Paleoanthropologists are nonetheless debating precisely why you’ve determined to do such a factor, and also you virtually definitely don’t have a vacation spot in thoughts, however for now we’ll take it with no consideration that you simply simply need to take a very, actually lengthy stroll. Virtually inevitably, you’ll come to the Levant, on the jap finish of the Mediterranean. From that essential geographical crossroads, you’ve bought some choices: you can head north by way of Syria and Turkey, then veer east into Asia or west into Europe. You could possibly additionally strike out east, throughout the northern finish of the Arabian Peninsula.
That was a greater choice then than it sounds now. On and off throughout the Pleistocene, the Arabian Peninsula had a wetter local weather than it does as we speak. Proof from historic sediments, pollen, and animal fossils all counsel that as we speak’s deserts had been as soon as grasslands and woods, crossed by rivers and dotted with lakes just like the one at Alathar within the western Nefud Desert.
Consequently, the Arabian Peninsula has been an essential route for hominins’ enlargement past Africa, which began with Homo erectus and ultimately ended with Homo sapiens. 300,000-year-old stone instruments at one web site within the Nefud most likely mark the presence of an early wave of hominins, most likely Homo erectus. And final yr, archaeologists discovered an 85,000-year-old fossil finger bone within the Nefud—the oldest instantly dated Homo sapiens fossil wherever outdoors Africa or the Levant. The footprints at Alathar counsel that our species had reached Arabia even earlier.
How can we make sure? Neanderthals had wider, heavier ft with shallower arches in comparison with most Homo sapiens, and the proportions of the prints at Alathar look extra like Homo sapiens ft. There’s additionally no hint of anybody else within the area at the moment (up to now), so our species seems to be extra doubtless. And based mostly on the completely different sizes of the tracks, the group most likely included not less than two or three folks.
Utilizing a way known as optically stimulated luminescence, paleoecologist Mathew Stewart of the Max Planck Institute for Chemical Ecology and his colleagues dated the layer of sediment simply above the layer with the footprints, in addition to the layer slightly below them. Over tens of 1000’s of years or extra, quartz grains lure electrons of their crystal construction (the electrons find yourself trapped as a result of pure radiation excites them into bouncing round till they get caught). When scientists come alongside and zap a sediment pattern with mild, these electrons get launched, giving off photons within the course of. By measuring the photons, scientists can inform how way back a rock or layer of sediment final noticed the sunshine of day. That offered a useful set of brackets on the attainable age of the footprints: someplace between 112,000 and 121,000 years outdated.
Simply passing by way of
Again then, Alathar was a shallow lake in a low spot between dunes. The silica fossils of single-celled algae within the footprint layer counsel that when the small group of individuals visited, the lake was within the technique of drying up because the local weather shifted. But it surely nonetheless held sufficient freshwater to supply an interesting cease within the arid panorama for people and for a menagerie of different Pleistocene wildlife.
The bottom across the lake deposit is “closely trampled,” with not less than 376 tracks from varied animals. Lots of the tracks had been muddled by erosion and trampling, however the 177 that Stewart and his colleagues might determine offered a snapshot of the ecosystems early people had been a part of as they expanded into southwest Asia.
At Alathar, folks crossed paths with complete herds of elephants and camels, together with not less than one large buffalo and a wild ass. It’s doubtless that every one of these animals visited Alathar inside days and even hours of one another, as a result of footprints in mud are inclined to fade away shortly except they’re preserved in some way. (In case you’re an ichnology fanatic, it’s price noting that experiments in a mudflat present that human footprints lose their positive particulars inside about two days and turn into completely unrecognizable in 4.)
“Motion and panorama use by people and mammals in Arabia had been inextricably linked,” wrote Stewart and his colleagues.
Though each folks and animals walked in all instructions at Alathar—alongside the shore, to and from the lake, and on different paths—the tracks all ultimately make their approach from north to south. Stewart and his colleagues counsel that the big herbivores like elephants, camel, and buffalo might have been shifting south to comply with a seasonal shift in rainfall. Trendy elephants in east Africa do the identical factor as we speak, they usually comply with chains of lakes just like the chain Alathar was part of 120,000 years in the past.
The small group of people that handed by the lake at Alathar might have been following the water, the herds, or each, however they didn’t keep lengthy, in any case. There’s no hint of stone instruments, animal butchery, fireplace fires, or the rest that may point out folks really lived and labored right here. At different historic lakes within the Nefud, archaeologists have discovered stone instruments and different proof that individuals caught round for some time, however not at Alathar.
“It seems that Alathar Lake was solely briefly visited by people,” wrote Stewart and his colleagues. “It could have served as a stopping level and a spot to drink and forage throughout long-distance journey, maybe initiated by the arrival of dry situations and dwindling water assets.”
Science Advances, 2020 DOI: 10.1126/sciadv.aba8940 (About DOIs).