Andy's Blog: Abdur, Eritrea

Coral Reef Foraging Off the Red Sea (125,000 years ago)

For today’s 100,000 year old site, we’re traveling to the coast of the Red Sea in what is today Eritrea. The coast by the site of Abdur was lined with ancient coral reefs. Towards the beginning of the Eemian Interglacial (a period in between glacial periods much like what we’re experiencing right now), 125,000 years ago, these reefs were abundant with large rock oysters. These would almost be cemented to the coral reefs. They made visible and tempting targets for humans, who were able to see them during low tide. In order to harvest these oysters, they would take humanity’s most trusty heavy duty tool, the Acheulean Handaxe, and chip them off to separate them from the coral. They then used smaller, more modern “Middle Stone Age” stone blades to get at the insides. At least that’s what some scientists think might have happened, since they basically found these tools embedded in old coral reefs, which are easy to date.

One of the remarkable things about this event are that it was for a time, the oldest known instance of humans harvesting marine life. It’s also one of the last known uses of the Acheulean hand axe, which was first used over a million and a half years ago. Its position is also near a land bridge some scientists think used to exist during the low sea levels of the ice age that allowed humans to migrate from Africa to Asia towards the southern tip of the Red Sea, so scientists are interested in seeing if the tools found here are similar to those found in Asia at the time. The site is also important because it gives us a glimpse into the last time the Earth was as warm as it is today (in between glacial periods), which scientists try to study to predict what might happen today.

The Acheulean hand axe was first created at the time human hands had first evolved sufficient grasping strength to create them, by Homo Erectus 1.7 million years ago. They were the first stone tool created with sculpted symmetry. They were tear-drop or pear-shaped with a sharp point at one end. They were molded to fit into the hand and were a real all purpose tool. Often compared to the swiss army knife, they could slice through hides, cut through wood, or bash things good. I like to think of them like the smart phone of the day. I wonder if everyone had one and if they always carried them around with them? Near the fossilised reefs at Abdur, volcanic rock that was laid down my an eruption 0.7 to 0.9 million years ago in what is called the Buri Sequence. Here they found fossil remains of Homo Erectus, dating from that period and during the height of Acheulean Axe use. I wouldn’t be surprised if they found hand axes with the skeletons. By about 200,000 years ago, the hand axe had largely been replaced by more modern “Middle Stone Age” tools. You could do neat stuff with the new tools, such as fasten them to wood to make spears. The old handaxes still had some use however. Maybe it just wasn’t as frail as the newer more sophisticated tools. Good for wedging in betwen oysters and applying force to separate them from the surfaces they clinged to. As the Eemian period moved on though, the oysters were gone, likely due to climate change. They were replaced by smaller clams and other seafood could still be harvested, such as scallops, crabs, and sea snails, but with no need for a chipping tool. Then there was maybe no need for the hand axe anymore. It hasn’t been found in the geologic record since. Thus the longest used tool in human history was forgotten, and they had a new tool for any other use an old hand axe would be needed for.

We don’t actually know if the people who harvest oysters there were modern day humans. There we no human bones found. As far as I know, the only modern humans who used Acheulean Hand Axes were a population in Ethiopia 160,000 years ago. These were different enough from today’s humans to be considered by some to be a subspecies of modern humans. I wonder if the people at these reefs were related to them? We also don’t know for sure if they were harvesting the oysters, they could have just dropped their tools there, but it makes for a compelling theory. They likely got most of their meat from land animals, such as hippos and bovids, and maybe crocodile, based on some bones they found near some other tools.

At the time of its discovery in 2000, this was the oldest known good evidence of marine exploitation by early humans, 10,000 years earlier than the previous older at the Klaises River delta on South Africa’s coast. While these were found to be from a time of warmer weather, the discoverers speculated though that the adaptation to utilize marine resources was developed thousands of years earlier as a way to cope with the desert conditions that existed in the interior of Africa during the ice ages. Sure enough, scientists later found evidence of marine exploitation far earlier during the previous ice age 165,000 years ago near Pinnacle Point on South Africa’s coast. I’m going use my imagination a bit and imagine that the people at Pinnacle Point spread out from the southern tip of africa and spread along the whole eastern coast, spreading their new lifestyle of eating sea food all along the way, and within 40,000 years had reached the Red Sea, where they left tools in coral reefs. Wonder if they’ll ever find anything that might support that theory? It does seem likely that by 100,000 years ago though, that marine adapted lifestyles were found around the world. They have even found Neanderthals in Portugal and Italy who were harvesting sea resources. I wonder how this lifestyle compares to the spread of agriculture, with it being developed independantly in many places around the world, but also spread from culture to culture and via migrations. Note that this predates fishing as we know it. It was the shellfish around the world that could be found along the beaches that were human’s targets. They also collected the shells for tools (such as containers, scrapers, and something to hold paint in) and ornamentation in the form of beeds.

Another thing about this site that interests scientists is that it’s close to where modern humans would have gone through during an early migration from Africa to the southern areas of Asia that happened between 130 and 100 thousand years ago. We’ve known for a while by studying the dna of our own maternal and paternal lines that our ancestors left Africa into Asia about 60,000 years ago, but newer fossil finds and fossil dna analysis have shown that there was an earlier migration of modern humans 130 thousand years ago. There are two basic routes into Asia scientists think humans may have taken. The Northern Route is over the land at the northern reaches of the Red Sea on the Sinai Peninsula and through Israel, while the Southern Route is on the southern tip of the Red Sea across the narrow Straight of Bab-el-Mandeb, across which is Yemen and the Arabian Peninsula. Stone tools found here and in the Asfet site across the Gulf of Zura, about a kilometer away, are similar to those found in eastern africa. These are similar to those found on the Arabian Peninsula here. Since it seems that humans were adapted to the coast, they could have gone south from Abdur and crossed the Bab-el-Mandeb into the Arabian Peninsula and then continued along the southern coast of Asia all the way to southern China. Some scientists think that the whole “Out of Africa” thing is a bit bogus though, with humans evolving across all of Afro-Eurasia, crossing the continents relatively regularly, so that you can’t really say modern humans originated in Africa.

Lastly, one of the other reasons scientists are trying to study this site is because coral reefs are indicators for past sea levels. The world was in an the Penultimate Glacial Period from 195,000 ago to 135,000 years ago. The Eemian Interglacial then began, and lasted for 15 thousand years, until the Last Glacial Glacial Period began. We then entered the current Holocene Interglacial, about 12,000 years ago. Well, we’d be in an interglacial if man made global warming doesn’t prevent the next glacial period from starting, which if the Eemian is any indicator, could be in 3000 years. The Eemian was about 1-2C hotter than it is today. Since some scientists are predicting that within a hundred years our temperatures will also be 1-2C hotter than it is now due to climate change, looking at the sea level that existed during the Eemian could give us a preview at what the sea level might reach when we get hot. The sea levels were definitely higher in the Eemian than they are now. The fact that the fossilised coral that they are now studying at this site is now on dry land is a testament to this fact. Since certain types of coral are near the surface of the water, scientists use them to estimate the sea levels of the past. Estimates using coral indicates the sea levels were about 6-9 meters above current level. These give rather crude estimates though, since the coral can compress over time and you don’t know exactly how close the top was to the surface of the water. More recent studies done by studying the remains of microorganism that live at the surface of water found along the walls of caves in Greece found that the highest the sea got was the lower estimate of 6 meters above today. Basically, if you find a micro-organism that lives at a the surface of the water against a rock wall and are able to carbon date it, you can then look to see how high up the wall it was to estimate the sea level at that time. Studies from Antarctica show that the West Antarctic Ice Sheet collapsed at the very beginning of the Eemian Interglacial, which caused the sea level to jump 6 meters above today’s value. The sea level then gradually lowered to 2 meters above today’s value for most of the rest of the Eemian, after which it dropped again. This kind of gives us an idea what might happen if the West Antartic Ice Sheet collapsed today. Guess we gotta hope it doesn’t any time soon. That’s a lot of beach side property lost. They’re still working out the kinks and cross checking all their results and doing new studies, so we’ll see what they ultimately conclude about how much, how fast, and when the seas rose and what that might mean for today.

Sources:

News Stories -

Earliest known sea food (May 2000)

https://www.esci.umn.edu/orgs/mil/Publications/49-Walter-Nature.pdf

https://news.utexas.edu/2000/05/02/humanitys-first-oyster-bar-eritrean-stone-tools-push-back-dates-of-earliest-use-of-marine-resources/

https://www.sciencedaily.com/releases/2000/05/000531070849.htm

Eritrea Coast Results (Jan 2002)

https://academia.edu/resource/work/4614330

Acheulean Hand Axes Found (Jan 2004)

https://www.researchgate.net/profile/Robert_Walter2/publication/222022767_Stratigraphy_palaeoenvironments_and_model_for_the_deposition_of_the_Abdur_Reef_Limestone_Context_for_an_important_archaeological_site_from_the_last_interglacial_on_the_Red_Sea_coast_of_Eritrea/links/5d23930c299bf1547ca4de5e/Stratigraphy-palaeoenvironments-and-model-for-the-deposition-of-the-Abdur-Reef-Limestone-Context-for-an-important-archaeological-site-from-the-last-interglacial-on-the-Red-Sea-coast-of-Eritrea.pdf

Reconnaissance (Aug 2007)

https://academia.edu/resource/work/530867