Back in October, I commented on the fairly amazing find of human footprints at Lake Otero in New Mexico, which Bennett et al (2021) argue are 23k years old. As I said at the time, whether the footprints are 23k, or 15k, or 12k years old, it is still an amazing find. However, if they do turn out to be 23k years old, it would not only be amazing, it would be redefining for the archaeology of the Americas.

Now Madsen et al (2021), who have their own contested early date of 16k at Cooper’s Ferry, Idaho, have published a short but pointed critique of the original Lake Otero claim in Science, to which Pigati et al (2022) have replied. Not surprisingly, Madsen et al focus on the carbon dating of the Ruppia cirrhosa seeds on which Bennett et al primarily rely for their conclusion that there were people at Lake Otero 23k years ago.

Madsen et al. worry that Ruppia cirrhosa, an aquatic plant, “use dissolved inorganic carbon (DIC) in their photosynthesis and can date thousands of years older than their true age”, and that there is “ancient Ruppia seeds from shallow lakes, 1 to 3 m deep, dating thousands of years too old.” This would create a site-wide systematic bias in the carbon dates, and the footprints would therefore be much younger than 23k years, perhaps by as much as 5-10k years, which would put them comfortably in the range of ages for well dated early sites in the Americas.

To this, Pigati et al respond that “the distinct seed layers we sampled were positioned in gypsum-rich alluvial sediments that overlie the lake sediments”, and paint a scenario in which lake margins are periodically exposed by varying lake levels, and in which people and animals walk in much shallower water, perhaps a few centimetres, trampling Ruppia plants and seeds in the process.

In other words, they suggest that the seeds were deposited when the water was much shallower, and that those conditions would not have favoured a reservoir effect that would lead the seeds to give deceptively older ages. They rely again on the fact that some of the seeds are found in some of the human footprints to place the creation of the footprints and the deposition of the seeds as part of the same event. Incidentally, they still don’t categorically state that some of the seeds found in the footprints are among the ones actually dated. Still a minor problem, but still an irritant.

One of the other possible explanations that should be ruled out of course, is that the footprints were formed and preserved in a shallow water period, and that the seeds were deposited in and around them much later, in a deeper water period, during one of the periodic inundations of the lake margin. The seeds could then give dates that are too old.

Pigati et al. sort of address that indirectly by pointing to “discontinuous, thin (<1 cm) lenses of clay interbedded with gypsum-rich silt and sand” left by the periodic inundations, which we suppose would then lie between the footprints and any seeds found directly above them. But there are a number of scenarios that would still accord with the evidence, which involve erosion events in between inundations.  In pre-emptively ruling this out as unlikely, Pigati et al. seem to have more confidence in the fine grained nature of the paleo record than I do, whether archaeological or environmental.

To the broader critique that “paleogenetic estimates suggest that the Americas south of the ice sheets were not occupied by humans until after ~20 ka” (in support of which Madsen et al. not surprisingly cite their own contested date of 16k at Cooper’s Ferry), Pigati et al. reasonably reply that the new findings at Lake Otero “must be judged on their own scientific merit rather than whether they agree with prior findings.” To which I say, fair enough.

In general, Pigati et al. don’t really address Madsen et al.s critique, beyond saying, that they already accounted for all that in their original paper. I am still left with some definite questions. The risk of site-wide systematic bias in carbon ages is still there, as far as I can tell. Madsen et al. do a good job of articulating it, and Pigati et al. do no more than they did in the original paper to lay it to rest.

Regardless, a fantastic find from which we can learn a great deal, and which will be significant to many for many different reasons. But as far as I am concerned, the age of the footprints at Lake Otero is still uncertain.


M. R. Bennett, D. Bustos, J. S. Pigati, K. B. Springer, T. M. Urban, V. T. Holliday, S. C. Reynolds, M. Budka, J. S. Honke, A. M. Hudson, B. Fenerty, C. Connelly, P. J. Martinez, V. L. Santucci, D. Odess, Evidence of humans in North America during the Last Glacial Maximum. Science 373, 1528–1531 (2021).

J. S. Pigati, K. B. Springer, M. R. Bennett, D. Bustos, T. M. Urban, V. T. Holliday, S. C. Reynolds, D. Odess, Response to Comment on “Evidence of humans in North America during the Last Glacial Maximum”. Science 375 (2022).

D. B. Madsen, L. G. Davis, D. Rhode, C. G. Oviatt, Comment on “Evidence of humans in North America during the Last Glacial Maximum”. Science 374 (2021).

7 thoughts on “23 k year old footprints at Lake Otero, New Mexico, Round 2

  1. I understand the comments, but I would like to know what difference it means to the average guy. Whether the footprints are 5,000 or 150,000 years old is insignificant when you are struggling to put food on the table, or getting shot because of your skin color, or dying of covid beaue you co-worker does not want a covid shot. I think we have more realistic day to day life issues to deal with than how old some footprints are. We will survive no matter how old the footprints are, but we may not because of the other issues.


  2. I don’t disagree with anything you said. Just like you, I am doing my job. I do think it is work that matters. How we see the past organizes how we behave in the present, how we treat each other, who has land rights, etc. This is worth a longer post. Let’s see what I come up with.


  3. The search for truth ends with partisan politics which blinds its participants accordingly. If your commentators wish to engage in it, you should charge them for ad space. Political hyperbole does not belong on an academic site and allowing it not only discredits your endeavors with perceived bias, but over time would also turn your board into a cesspool of bickering combatants. On the bright side, you’ll get more clicks though…


  4. Not sure that anything I said was a “partisan political statement” It was a scientific statement based on facts. I understand that your field requires (or desires) answers about where we came from. I have no qualms about that. But to pick an opinion apart for some vague reason when we could be spending that effort in trying to fix where we are and not where we came from seems a bit more important. That is my opinion and this site does allow opinions (which is where this whole conversation started).


  5. Who are you quoting Bruce? Do you understand how quotations work? Let me show you…

    You basically come onto an academic board pertaining to archeological issues and write: “I think we have more realistic day to day life issues to deal with than how old some footprints are.” So given that statement, it is apparent that you did not come here to discuss Archeology. No, you wish to go on about “more important” things, deeming your political hyperbole to be “scientific” and “based on facts”.

    Science is a method of finding truth Bruce. It is not truth itself and cannot be used as a principle to convert your opinions into facts. As for those opinions… well Bruce, you are certainly welcome to them, however off topic within this venue. As such, can you not see that it is completely out of place for you to request that our host give up his interests in favor of your politics?

    Now let us not become bickering combatants. Please.


    1. I apologize for intruding on your dusty, private, little world. I always thought that academics included asking questions, which is what I did. As you recall, my basic question was “why is this so important considering the mess this world and his country is in right now”. Hope I met your approval with my quotations. What I got was verbal abuse, never got an answer to my question. You must not have an answer. I hope to God that the real world does not catch up with you, does not sound like you will be able to handle it. Bye!


  6. “Hope I met your approval with my quotations.”

    Sorry Bruce. Once again, you’re quoting something that wasn’t written within this discussion. What you are seeking to do is in fact known as paraphrasing, which does not involve quotation marks. Please also note that this is not my “dusty, private, little world”. I’m not the host of this site. Our host has been very kind to you, and perhaps we can both learn from him should your goodbye not be long lasting.


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