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Homo naledi was a hominid that has recently made the news, in part because the discovery of a large number of fossils appears to suggest ritual "burials" by a species from 2.5 million years ago, significantly predating those of H. sapiens.

The "burial chamber" was found in a cave system at a depth of approximately 30 meters. Given that there should be zero ambient light at that kind of depth, it seems to me that either H. naledi was very strongly motivated to bury their dead in that particular location (which makes the burials even more amazing), or the chamber has changed it's depth and become significantly deeper than it would likely have been 2.5 million years ago.

Is it likely that a cave chamber can change it's depth significantly over 2.5 million years?

EDIT Added a view of the layout of the burial location cribbed from the New Scientist article... just because it shows how motivated H. naledi must have been to put their dead where they did.

enter image description here

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  • $\begingroup$ Interesting question. If the cave hasn't changed in 2.5 Ma it then begs the question, "did H naledi use fire sticks, or similar to illuminate the cave & chamber during burials?". From a long section I've seen of the cave there's a convoluted path to get to the chamber where the bones were found. $\endgroup$ – Fred Sep 15 '15 at 8:07
  • $\begingroup$ The latest New Scientist has a more indepth write-up than the typical news media ( newscientist.com/article/… ). Basically, the date is currently unknown - it could be as young as 100ka. Also some researchers (not the authors of the paper) think they may have bones from two different species. $\endgroup$ – winwaed Sep 15 '15 at 13:11
  • $\begingroup$ I don't see the vertical scale here, but another entrance that has been sealed since sounds more plausible - and this is pure hypothesis on my side. $\endgroup$ – Jan Doggen Sep 15 '15 at 18:59
  • $\begingroup$ @Jan Doggen - Using the 12m vertical shaft as a guide it appears to me that the vertical scale is the same as the horizontal scale. Assuming that is the case the top of the vertical shaft is itself about 15m underground. $\endgroup$ – Doug B Sep 15 '15 at 19:06
  • $\begingroup$ Just a comment on South Africa in general: that most of the landscape is pretty old, so erosion has been minimal over the last few million years in most places. I will try dig up some of the cosmogenic dating that has been done, but short answer: probably not. $\endgroup$ – mtb-za Sep 16 '15 at 14:25
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2.5 million years is more than enough time for things to change drastically some places, in New Zealand there are mountains whose sediments were seafloor ooze a million years ago, but Africa is not usually one of them. Africa's geology is normally far too stable to show major changes on that short a timescale. In the normal course of things a given position in a cave system becomes shallower as time goes on due to surface erosion. What I can find on the Monte Christo Formation that holds the Rising Star Cave and the surface survey here suggests that there have been no major deposition events since the caves were formed, this would suggest that in fact the fossils were even deeper under ground when they were deposited.

It is however possible that there was a transient hole in the roof of the cave that has since filled with redeposited minerals and is no longer evident, such are not unheard of in karst terrain and would have supplied light to great depths. The bones may also have originated closer to the cave entrance and been swept deeper into the system by flooding at a later date.

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From the Wikipedia article about the cave:

"A portion of the cave, used by the excavation team en route to the Dinaledi Chamber, is called "Superman's Crawl" because most people can fit through only by holding one arm tightly against the body and extending the other above the head, in the manner of Superman in flight.[2][5]

The Superman Crawl opens into the "Dragon's Back Chamber," which includes an approximately 15 m (49 foot) exposed climb up a ridge of a sharp-edged dolomite block that fell from the roof sometime in the distant past. This block is the so-called Dragon's Back, so named because the climbing route appears to progress from the tail to the head along the spiked spine of a mythical beast."

So probably the last two obstacles, the dragon's back crawl and the last steep section, weren't there. Likely they could have just walked across those before the ceiling fell in. And possibly there might have been an easier route into the cave that's now hidden under the rockpile.

This isn't an actual answer, but the quote was too long to fit into a comment.

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