Last year I wrote about the strange rubbing boulders of the Atacama desert. In that post I relayed the story of these strange large boulders that are found scattered in a high valley in the Atacama desert. That desert is one of the driest places on earth with the area that these particular boulders lie experiencing an average of only 3mm of rain per year. The research on these boulders clearly demonstrated that these boulders were not washed into place nor blown to their present locations. In addition they have these funny girdled erosion pattern on their sides. One providential event led the researchers to the probable explanation for all the odd features of these boulders. While investigating a group of these boulders there was a magnitude 5 earthquake centered not far away. The researchers report that the boulders suddenly started to rock back and forth and some of them started to slowly turn on the desert floor and a very loud sound of rocks bumping into each other could be heard. Suddenly a plausible and observed mechanism to explain the presence of these rocks became clear. All of this I reported before and I use now as a backdrop for exploring some of the further ramifications of these rocks to the age of the earth.
A press release summarizing the publication resulting from the work of several researchers (Quade et al (Geology, 2012, see reference below) included the following:
“The whole story appears to be that the boulders tumbled down from the hills above — probably dislodged by earthquakes. They accumulated on the sand flat, with no place else to go. Quade compares the situation to a train station where people are crowded together closely, rubbing shoulders as they waiting for a train. In this case the boulders have been stuck at the station for hundreds of millennia and the train never comes. So they just get more crowded and rub shoulders more over time.
Analyses of the boulder top surfaces suggest that they have been there one to two million years. That age, combined with the fact that seismic activity in the area generates a quake like that Quade witnessed on the average of once every four months, suggests that the average boulder has experienced 50,000 to 100,000 hours of bumping and grinding while waiting for that nonexistent train.”
So apparently this is a case of the one the worlds largest natural rock tumbler, albeit a rock tumbler working at slow speed over a long period of time. From the picture above you can see that some of these boulders are many yards away from the next closest boulder. It may takes hundreds or thousands of years for them to move by vibration over to another rock and come into contact it, much less have enough contact to produce appreciable erosion.
Atacama Boulders in the Context of a Young Earth?
I am not sure how creation scientists would try to explain these boulders but I do know that flood geology models would require that the boulders have been formed after a global Flood and thus be less than 6000 years (or 4000 for the extra-literal young earth creationists). Why after the noahic flood? Because these rocks are granodioritic rocks which is a fancy way of saying they are igneous and in this case volcanic rocks. And these volcanic mountains are extruded out on top of tens of thousands of feet of fossil-bearing sedimentary rock. The young earth creationist then would expect that the sedimentary rock were laid down by the flood followed by the extrusion of volcanic material to form the mountains and then cooling and erosion of the mountains to form these high elevation flat bottom valleys. So the solidification into rock, fracturing and then falling of rocks into the valley must have taken place after the waters of the flood receded. The conventional geological explanation for these rocks finds that these boulders have been shaking and moving down this mountain out into the valley below for at least a million years. How can a YEC compress this action into just 4000 years? I really don’t know because there is no evidence of water being in this area for a LONG time and although there is wind it doesn’t explain the distribution. I expect that they may try to use the earthquake explanation for these boulders as well but I’m not sure. This story has been out for almost a year but I’ve yet to hear a young earth creationist comment on it yet.
The physics and chemistry of erosive processes tells us that it would take a lot of jostling/bumping to cause this much erosion so I expect that the explanation might be that some time after the flood this area must have experienced 100s of times higher rates of earthquakes and possibly larger ones such that there was nearly constant vibration of the ground for several hundred years followed by reduced earthquake activity to the point we see today. Here we have another example of assumptions about rates that separates the conventional geologist from the young earth geologist. In this case the assumption of long term consistency of earthquake rates is not unreasonable while vastly different earthquake frequencies in the past is not obvious from any of the evidence (here or elsewhere). Only a belief that these rocks could not have existed prior to 4000 years ago because of a global flood would cause anyone suggest, or even look for, another solution to how these rocks came to appear as they do. The formation of these rocks in this pattern with these girdled erosion patterns is very difficult to explain without the availability of large amounts of time as part of the equation. YECs are fond of saying that not only is the Earth is young but the evidence actually points to a young earth not just can be interpreted in a young earth worldview. This example shows just the opposite, no-one would look at these rocks and say that they speak of a young earth, rather they can only be forced into a young earth worldview which is no easy task.
Are there other ways to date these rocks aside from estimates of erosion from bumping into each other?
Yes! A lesser known from of nucleotide dating is Cosmogenic Nucleotide Dating (See HERE for more details). This is a form of what has been called surface exposure dating. The idea is that these rocks were at one time part of a rock wall on the mountain and not exposed to the surface (eg. more than meter of rock at least was covering them). As soon as the rock above them fell away and they became exposed to the surface they also became exposed to cosmogenic radiation (cosmic rays and eventually nuetrons). These then bombard the surface of the rock and alter the nuclear composition of those rocks. Over time rocks exposed at the surface will show more and more differences in their isotopic ratios. Therefore, measurements of the differences of the original source rock that hasn’t been exposed with rocks that have been exposed can be used to estimate how long the latter rocks have been exposed. In a study that used this method along with other methods to estimate ages (see reference to Placzek et al 2010 below) the researchers concluded that their boulder fields were a bit over 1 million years old with other boulder fields in the Atacama desert to be up to 2.6 million years old.
How confident are you in those dates for the rocks?
A young earth skeptic probably will say that these methods are just another form of radionucleotide dating and thus the methods assume constancy of rates such as cosmic rays over time. But there is independent evidence that this method is fairly reliable at giving general ages (ie. 5000 vs 500,000 vs 5 million years). In this study the age of the sediments of the hills in the Atacama were being aged to test predicted erosion rates over time. If the hills were eroding quickly then they would constantly be exposing new rocks/sediment which should give very young exposure dates. What they found is that there are sediments in the Atacama desert that appear to have been exposed for over a million years suggesting very very low erosion rates over time. What if this method were totally bogus? Maybe the desert is really young. If it were bogus then we should find that sediments in other deserts in the world should also exhibit very old ages because they should have experienced the same presumably changing rates of cosmogenic radiation but the ages of many other desert surfaces in other parts of the world are shown by the same method to be much much younger. This suggests that material has been moved around indicating the climate of that area has been different in the past. Cosmogenic dating frequently corroborates the dating of rocks by other methods and other studies that have been used to estimate how long landscapes have remained stable. In this case we have rocks that appear to have needed a long time to have eroded as they have and the dating suggests that these rocks have been lying on this desert flood exposed to the surface for a very long time. Had all these rocks simply gotten jostled off the mountain recently by a very large earthquake, they would lack the signature erosion and isotope differences from the rocks from which they originated.
The Atacam desert attests to a series of historical events that have taken place over long periods of time. Any explanation that requires a short period of time is going to need to explain all of these observations not just one of them. Earthquakes and long periods of time in a climatically stable place seem to provide a very strong explanation for the observations that have been made of rock formations in this desert.
What about wind erosion? Could that cause some of the smooth sides of these boulders?
No, the erosion on the sides of these boulders is clearly from contact with other rocks and not from sand blasting. What would we expect from wind-born sand erosion. Look at the picture below (and the featured image for this post) of another rock formation in the Atacama desert. This is one of many “tree” rocks which appear in some areas of the desert. These are rocks that are clearly shaped by wind-born sand erosion. In this case the sand is near the surface and so any rock that stands more than 6 feet tall will experience greater erosion near its base creating these odd formations.
Placzek, CJ, A. Matmon, DE Granger, J. Quade, and S. Niedermann. 2010. “Evidence for active landscape evolution in the hyperarid Atacama from multiple terrestrial cosmogenic nuclides.” Earth and Planetary Science Letters. 295: 12-20. This article provides the evidence for the age of the stones that have the funny erosion patterns. Cosmogenic nucleotide dating is reported.
Quade, J. P. Reiners, C. Placzek, A. Matmon, M. Pepper, L. Ojha, and K. Murray. 2012. “Seismicity and the strange rubbing boulders of the Atacama Desert, Northern Chile” Geology 40: 851-854.