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Posts Tagged ‘Andes mountains’

We believe that the Andes Mountains are 25 -30 million years old, or at least that is their start date, based on a variety of dating techniques. They took a long time to rise. But for a while, they were believed to be much younger, perhaps 7-8 million years old. The younger date is interesting because it provides a study in how easy it is to draw a mistaken conclusion from data that are good, but don’t quite cover all the bases.

The younger year date was based on the steep rise in the near-pure 16O in the sediments east of the Andes or in lake-bottom sediments in the area. Since such sediments come from the mountains, they represent chemical processes on the mountaintops; and since the proportion of 16O remaining in a cloud is greater the higher the cloud rises before dropping all its rain, the sudden increase in 16O  sediments seemed to suggest a sudden rise in the mountains, — 4,000 feet in 4 million years.

This was not an unreasonable inference, though it was an awfully fast uplift.

However, in due time, someone pointed out that a simple increase in rainfall will pull the 18O out of a cloud leaving a higher proportion of 16O, and thus an increase in rainfall can change the isotopes available on the mountaintop just the same way as an increase in height. Was there an increase in rainfall during the rise of the Andes?

There was, and they did not spurt up in 4 million years, but took perhaps four times that long. All this just to say that there’s always a new twist, always something new to learn, always an unexpected turn of events in the sciences. You really want several converging lines of argument, not just one, no matter how carefully researched.

On the other hand, none of these events could have prepared anyone for the image of our Lady in the rocks of Las Lajas, at the back of a cave near Ipiales Columbia. And this brings me to an entirely different topic, a topic that is not specially related to any particular science, but to the philosophy of science. It is a topic that I would like to explore with this minor discussion of the Andes Mountains, the miraculous image they house, and the possibility of scientific error and correction all in the background.

What is a miracle?

How can it be defined?

 

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Geology of Colombia South America

After reading about Our Lady of Las Lajas, (our Lady of the Rocks) I decided to learn something about the geology of Colombia, particularly around Ipiales. What sort of stones might there be in Colombia, I wondered, and are any of them deep blue shales? Here is the Las Lajas image, composed entirely of stone, except for the crowns, added later and seeming somewhat adrift on the glorious heads of the mother and child. (The other two figures are St. Francis and St. Dominic.)

Our Lady of Las Lajas 02

Lying as it does at the foot of the Isthmus of Panama. Colombia has the distinction being formed at the intersection of at least three tectonic plates: the Nazca Plate under the Pacific Ocean, the Caribbean Plate on the eastern side of the isthmus, and the South American plate to the south. The Nazca plate apparently first pushed against the South American plate in the deeps of time, over 500 million years ago, which is about when the supercontinent of Pangaea formed and before it broke up into the northern semi-supercontinent of Laurasia and its southern counterpart, Gondwana.

Laurasia included North America, and Gondwana included South America. Both of them had to break apart along a north-south seam, releasing Eurasia and Africa westwards, whilst also coming together from north to south, thus creating the double continent of the Americas, with Panama at their juncture.

Panama, therefore, is at the junction of several tectonic plates whose collisions belong to various episodes of tectonic shift over half a billion years. Looking today from above, one may think of it as a delicate strand that connects two continents; in fact it is probably not much more delicate than Italy which also lies at a junction of three tectonic plates a fact which accounts for its world reputation in beautiful marble.

The Andes mountains are the most striking feature of Colombia and also the location of most of her cities. The west coast is jungly and wet; the eastern plains range from something like savannah in the north, to the upper reaches of the Amazon jungle in the south; but even the drier regions have annual flooding that makes farming difficult. So the mountains are the location of Colombia’s cities and it is rugged going from place to place.

The city of Ipiales is on the western side of the Andes Mountains, just above the jungles of the Pacific coast, and just over the border from Ecuador. The little town of Potosi is six miles east. Perhaps both towns were small in 1754.

Blue shales

I still do not know anything about blue shales. Somerset England has a lovely formation from the early Jurassic, called the Lias. The stone is very blue.

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