Methods and the sea foam of doom!

Last weekend, Curtis Marean (the archeologist in charge of Mossel Bay and Pinnacle Point) took us on a five hour tour of the caves so we could get the bigger picture and some context for the work we are doing.

Curtis has been working in these caves for over ten years, and he is most famous for the cave labeled PP 13B. This cave shows some of the earliest evidence for humans exploiting shellfish and for the mining of ochre, which is used for making pigments. But Curtis believes that these caves will also have some of the earliest fossils from Homo sapiens dating back to around 191,000 years ago, a period classified in archeology as Marine Isotope Stage (MIS) 6. MIS is a dating technique that uses oxygen levels from core samples to distinguish between different glacial periods in earths’ history.

Along with my general love of caves and spending time in them, the part of the tour I found most interesting was Curtis’ explanation about why he chose these particular sites for excavation. He took us into each one and pointed out the geological features he noticed when he first saw them, and what he deduced from those features about why there may have been valuable archaeology in them.

One of the first things we learned is that during MIS 11, about 424,000  years ago, basically all of the ice on earth had melted and the oceans were about 20 meters (65 ft.!) higher than they are today. This is the highest they have ever been, or ever could be. At MIS 4, or about 71,000 years ago, we had another mini warming event in which the oceans rose about 12-13 meters. This means that any caves lower than 12-13 meters above sea level would have been washed clean of any artifacts dating to before 71,000.

To demonstrate this, Curtis showed us this cave, and asked us what we though the white stuff cemented onto the walls were.

These walls were roughly 30 ft. high, and the white blobs were rock hard with a bumpy, coney texture to them. He told us that when he first saw them, he had no idea what they were either. He asked six of the best geologists he knew and got six completely different answers. So they sent a sample off to a lab and got the results back a few weeks later: it was petrified coral. The entire cave had once been the bottom of the ocean long enough for coral to start forming. On top of that, the coney texture was caused by a particular kind of sea worm the burrows into living coral. Furthermore, this worm only lives in very tropical, temperate waters; much more tropical and mellow than the current sea of Pinnacle Point, which are pretty rough and fairly cold. These gross, white blobs tell us a lot about the life history of this cave.

So the caves had to be high. But they have to have features that made them attractive to hunter-gatherers for shelter, such as availability of food, easy access, and size. The sites also needed a high probability of being preserved and not succumbing to thousands of years of erosion. Curtis pointed out to us a whitish, nearly vertical line near the mouth of the cave and told us that this was actually a cemented sand dune.

They had dated it to 90,000 years old, when the ocean was much farther away than it is right now. Pinnacle Point is a cliff face right now, but when the ocean receded it freed up sediments and sand that are usually on the sea floor to become beach. The wind picked up these sediments and blew them up the cliff face, creating dunes that actually blocked the caves off at the mouths. Over time and with the slow drip of water, these dunes became hard and were cemented to the walls of the caves, and then eroded away. So for a good chunk of time, these caves were completely inaccessible from the outside world.

Combined with the location of these caves on the southern coast of Africa and what Curtis knew of paleoclimate and early, modern man, he decided to ask the National Science Foundation for what is called a High Risk grant. Not only did it pay off, but it became Curtis’ career defining project (I hope he wouldn’t mind me saying that) in which he, in combination with many other skilled people from all different fields, has actually created one of the longest running sequences of geological and archaeological recorded processes in all the world. Right now their timeline runs from around 160,000 years ago to 50,000 years ago, and they are looking to go even older once we are done excavating at PP56.

If you are still with me, congratulations. I recognize that a ton of this stuff will only be interesting to people who are interested in how this work is done, and I hope I didn’t bore you too much. We also got the chance to hike around on the rocks and over the ocean, which was a good time.

This week the Colorado crew was on kitchen duty. This means we got up at 5:30 am to make the group breakfast, cleaned up the breakfast at 6:20, out the door with everyone at 6:45, back home at 5 pm, washed out everyone’s lunch boxes, dinner with everyone at 6:45, back home at 8, and we washed everyone’s dishes at 9. It’s a long ass day that makes for a long ass week, and while I didn’t mind doing it, I’m glad it’s over.

It also rained like crazy all week, to the point that the people at Vleesbaii were actually rained out of the site for two days. They sat in the hostel for 8 hours sticking our plotted finds bags while we trudged around under a tarp in the rain. On Thursday, we kept watching the ocean building up a nice, frothy foam throughout the day. The storm had made the waves big and rough, and they pounded against the rocks pretty hard all afternoon.

Come time to walk back up, I noticed early on that one part of the path that the surf never reaches was wet, and had foam in the cracks of the rocks. The next part of the path had actual foam on the dirt. No big deal, I thought. Just get past this one part and then smooth sailing. I was wrong, as it turns out, because the sea foam was EVERYWHERE. 

It crawled up the beach and over our usual path into the foliage. At first we trudged through the bramble bushes, getting snagged by two inch long spines and trying to keep an eye out for snakes, in order to avoid the foam, but we just ended up tripping and falling into it sideways anyway, so we gave into our fate.

It was difficult because you were taking steps on uneven ground that you couldn’t see, and every time the tide came in or out the foam jiggled and undulated in this really creepy way all around us. It was one of the weirdest things I’ve ever seen.

When we got up top we found that only about six of us actually went through the foam. Curtis had called everyone else back to take the short cut, determining that it was too dangerous. He told us he had never seen the ocean like that before and that it was a result of the storm, spring tide, and high tide. Whatever it was, it was awesome.

More blog posts possibly in the week, defiantly by next Sunday. We’re doing Cango Caves next weekend and we’ve heard some amazing things, so I should have more amazing things to share. I don’t have time to struggle with homesickness, but I do miss you all terribly and I can’t wait to spend the end of the summer with you.