How the Andes Mountains Were Generated

Oxygen-isotope readings have for many years been used as the main source of information regarding the speed with which the Andes Mountains of South America rose. Many experts still believe that the mountain range rose quickly from the surrounding land, due to cataclysmic events caused by the tectonic plates nearby. But a new investigation appears to paint a different picture. According to the study, the mountains lifted themselves up over a much longer time than initially estimated.

The research group that arrived at this conclusion believes that the misunderstanding that was perpetuated for the past decades is not intentional. Rather, it stems from the fact that previous works failed to account for the effects of ancient rainwater, which may have skewed the results of the oxygen-isotope readings. Usually, the age of mountains can be assessed by using rain records that get stored inside the rocks themselves. However, finding these records and interpreting them correctly are two entirely different things, the group says, quoted by Nature News.

According to the new paper, it would appear that the Andes did not rise to 4,000 meters in just 4 million years, as stated by researchers in 2006. Rather, it's more likely that it took tens of millions of years for the range to grow this big. The study was conducted by University of Michigan in Ann Arbor climate scientist Cristopher Poulsen. Together with his team, the investigator conducted a more thorough analysis of the ratio of oxygen-16 and oxygen-18, the two main isotopes used to determine the age of the Andes Mountain Range. The chemicals are usually found in carbonate minerals at the bottom of dried-out, prehistoric lakes.

The expert says that previous investigation failed to account for a common phenomenon that occurs during raining. As clouds increase their altitude, they lose more water, and therefore large amounts of the most heavy oxygen isotopes are gone. They are therefore not inscribed in the records, which means that interpreting them becomes increasingly difficult. “There are other things that affect the isotopic concentration besides elevation. The more it rains, the more depleted the rainfall becomes in heavy isotopes,” the expert says.