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Saturday, September 20, 2014

It’s Interesting, But It’s Probably Not a Footprint

Posted by jlwile on June 5, 2013

A student sent me the video you see above. In it, a man highlights a South African geological curiosity. He says it is a giant footprint in rock that is somewhere between 200 million and 3 billion years old. He goes on to say that it is so amazing it should be drawing 20 million tourists to South Africa every year, but no one knows about it. He then takes you up a hill to the geological formation, and he shows you what appears to be a huge footprint in a wall of rock. The man points out the features of the “footprint,” and he ends the video with the statement, “There were giants on earth.”

I had the privilege of visiting South Africa in 2004. It is an amazing country, and the people there are simply marvelous. I would strongly recommend it as a vacation destination. However, I wouldn’t put this site on my “top 20″ list of things you should see. While it is an interesting geological formation, it is almost certainly not a footprint.

The first problem with the idea that it is a footprint comes from the type of rock in which it is found. The man in the video says that the rock is granite. Now, I am not a geologist, so I can’t be sure that the man is right, but the rock’s appearance is consistent with it being granite. Well, granite is an intrusive, igneous rock.1 What does that mean? An intrusive rock is one that is formed underground. An igneous rock is one that is formed from molten rock, such as magma. So if this rock is granite, there is no way it could harbor a footprint. The only time a foot could have sunk into it was when its temperature was several hundred degrees, and it was below the surface of the earth!

Even if the rock isn’t granite, there are other features that indicate this formation is probably not a footprint. The man in the video makes much of a shelf of rock that is found at the “toes” of the “footprint.” In his mind, this was caused by the giant pulling his foot out of the “mud” into which it sank. This pulled up some of the “mud,” piling it at the “toes.” However, if you look at the size of the rock shelf, it seems almost as tall as the footprint is deep. Try making a footprint that piles mud in front of your toes as high as your footprint is deep. It’s difficult, to say the least. At minimum, I can say I haven’t seen such a structure on any human footprint that I have found on the beach or in the mud. I also haven’t seen one in any fossilized human footprints (see here, here, and here, for example).

In addition, consider the size of the person needed to make the footprint. The man says the footprint is about 4 feet high. Well, a person’s foot length is about 15 percent of his or her height,2 so the person who left this footprint would have been about 27 feet tall! The Bible mentions giants, but it never mentions any that are close to 27 feet tall. The largest giant referenced in the Bible is probably Og, the king of Bashan (Deuteronomy 3:11). According to the Scripture, his bed was 9 cubits (13.5 feet) in length. Most beds are larger than their occupant, but only by a couple of feet. Thus, Og might have been as tall as 12 feet or so. The tallest giant whose actual height is mentioned is Goliath, and he was 6 cubits and a span, or about 9.7 feet tall (1 Samuel 17:4). In the end, the size of the person needed to make such a footprint seems to rule out the possibility that it is really a footprint.

So what is this thing that is being interpreted as a giant footprint? It is most likely a strange shape that formed as a result of erosion. If you look throughout creation, you will find many examples of this, such as Roccia Dell’Orso (the bear rock). This granite formation is a tourist attraction in the Republic of Palau:

Roccia Dell'Orso in the Republic of Palau, a remarkable granite formation (click for credit)

It is famous for being shaped a bit like a bear. However, it also demonstrates a common feature of granite that is exposed to erosion – cavernous holes that are technically called tafoni.

Most likely, that’s what this “giant footprint” is. It is probably a tafone (singular of tafoni) that just happens to be shaped a lot like a human foot.

REFERENCES

1. Joanne Mattern, Igneous Rocks And The Rock Cycle, Rosen Publishing Group 2006, p. 20
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2. Esther Beck, Cool Physical Evidence: What’s Left Behind, ABDO Publishing 2009, p. 18
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Comments

8 Responses to “It’s Interesting, But It’s Probably Not a Footprint”
  1. Evan Arcadi says:

    Wishful thinking and prejudice, the mother of all bad science and scientific fraud. On another note, this was a very interesting article.

  2. Kevin N says:

    It sort of looks like granite, but it is hard to tell with confidence. It would be an amazing feat (I almost spelled it “feet”) for the giant to implant his foot in molten rock as the granite was crystallizing perhaps thousands of feet underground.

    I’d put this in the same category as the rat on Mars:
    http://www.foxnews.com/science/2013/06/06/curiosity-rover-leaving-mars-rat-behind/

  3. jlwile says:

    Thanks for lending your expertise, Kevin. I had seen the “Mars rat” photo on Facebook, but I had assumed it was a joke.

  4. S.J. says:

    Here is a really interesting website with everything you might want to know about tafoni: http://www.tafoni.com/Welcome.html

    What I find most fascinating is the page about weathering rates: http://www.tafoni.com/Rates.html. It has a chart of historically observed weathering rates and rates that are inferred from the presumed time of exposure of the rocks, in other words, based on their geologic ages.

    I did some quick calculations, and maybe you can tell me if I’m off base here, but when I divided the average of the mean historically observed weathering rates (derived from the lower six values in the last column, and equaling .334) by the average of the ranges of the mean inferred rates based upon geologic dating (derived from the upper five values of the last column, and equaling .0011), the result was 296. In other words, observed historical rates of weathering are almost 30,000 percent higher than rates inferred from the time span calculated from geologic dating.

    If these calculations are correct, it seems to me that there are two possible explanations: 1) tafoni weathering rates reach a maximum almost instantaneously in terms of geologic time and then slow down a whole lot, or 2) there’s a problem with either the observed historical rate or the inferred rate based upon geologic dating.

    To me, the first possibility doesn’t seem likely because everything I’ve read about tafoni suggests that weathering is controlled by the atmospheric conditions and the type of rock, neither of which should drastically change over the span of geologic time.

  5. S.J. says:

    I need to clarify that last statement. Obviously, atmospheric conditions can change over the course of geologic time, but if the observed historical rates are the preferred benchmark, then they are so rapid compared to those derived from geologic dating, that the time span during which those presumed older rocks were exposed to tafoni-producing conditions must have been very short, geologically speaking.

    For example, the fastest mean rate inferred from conventional geological dating is .0002 mm/yr, and the slowest mean rate derived from historical observation is .15 mm/yr, which still gives a ratio of 7500%.

    To look at it another way, if we project the slowest historically observed weathering rate (.15 mm/yr) over the shortest period of time inferred from conventional geologic dating (50,000 yrs), 7500 mm of rock, or 7.5 m (about 23 feet), must have been weathered away. That seems way too much for the observed tafoni patterns to have been preserved.

    So it still seems to me that either tafoni weathering rates over long periods of time are much slower than observed weathering rates, or that the time period for old rocks to be exposed to tafoni-producing conditions must have been essentially instantaneous, geologically speaking. Assuming my math is correct, of course!

  6. jlwile says:

    Thanks for your analysis, S.J. There has been a lot of discussion about erosion rates in the YEC literature, and they do seem to present problems in an old-earth framework. Your analysis adds to that.

  7. Nathanael says:

    How do they know it was made naturally and not by man? Wouldn’t that be the most likely?

  8. jlwile says:

    Nathanael, if a person carved it into the rock, there would be signs. There would be chisel marks, sharp edges, or file impressions. I would have to visit the site to be sure, of course, but based on the video, I don’t see any evidence of it being carved into the rock.

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