Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

Many people agree that the Himalayas are so high because of the violent collision between the Eurasian plate and the Indian plate. But new research shows that the Himalayas were already quite high before the collision. In other words, in the period of geohistory before the collision, the Himalayas were higher than we expected. This is based on the oxygen isotope fractionation caused by climatic factors. at the same time, the proposal of this new view is bound to affect our understanding of paleoclimate.

(Noa Leach / tr. by Phil Newell)

Editor | Wen Jing

The Himalayas are known as the "roof of the world", with an average elevation of about 6000 meters. The main peak, Mount Qomolangma, is 8848.86 meters above sea level and is the highest peak in the world. Until now, we don't know much about the Himalayas, even those scientists at the forefront of the field. This majestic "roof of the world" has not reached its current height in the form we once thought, according to new research.

The study, published in the academic journal Natural Geosciences (Nature Geoscience), was signed by a joint team of scientists from China University of Geosciences and Stanford University in the United States.

The Himalayas were already high before the collision. It was previously believed that 45 million to 5900 years ago, the Indian plate collided with the Eurasian plate and the ocean part of the Indian plate subducted, resulting in a sharp increase in the height of the mountain range. In the new study, scientists believe that although plate collisions have contributed to the elevation of the Himalayas, the Himalayas were already high before the collision. The mountain began to rise much earlier than previously thought, about 61 million to 63 million years ago.

"experts have long believed that large-scale tectonic collisions, such as plate-to-plate collisions, are needed to produce an uplift with enough energy to form mountains the size of the Himalayas," said Daniel E. Ibarra, co-lead author of the study. "this study refutes this and pushes the field in some interesting new directions."

In the new study, scientists found that the Himalayas, located at the edge of the tectonic plates, were already high, about 3500 meters high, before the collision. This is much higher than the height once recognized by the scientific community, and the overall height has exceeded 60% now.

This initial uplift may have been caused by the marine part of the Indian plate, which was subducted at a low angle below the Eurasian plate, forcing the upper plate to uplift upward. These "small frictions" may have provided considerable energy and material before the two plates collided, allowing the Himalayas to rise to 60% of their current heights.

"the new study will rewrite all theories about climate and biodiversity in the past." Ibarra said.

The joint team that has discovered or will rewrite the history of the earth has adopted a new method to determine the ancient height of the mountains. The new method is inspired by oxygen isotope analysis, an existing technique for analyzing meteorites. The researchers used a new method to reconstruct the paleoclimate around the Himalayas and to determine the paleo-elevation of the mountains.

Warm and moist air climbs on the windward slopes of the mountains and cools and condenses into rain and snow. With the rise of warm air, the chemical composition of Rain Water will change. Heavier oxygen isotopes (containing more neutrons) will first fall from the cloud. At the same time, Rain Water, who landed near the top of the mountain, contained more lighter oxygen isotopes. This is called oxygen isotope fractionation, which results in a different proportion of oxygen isotopes in a substance.

Such isotopic differences are recorded in sedimentary rocks: the team measured the isotopic ratios of oxygen in sedimentary rocks in the Himalayas to deduce the paleo-height of the rocks.

The reassessment of the height of the mountains will "involve" the study of the entire paleoclimate, because the weather at that time, as well as the animals and plants living there at that time, will change according to the height and shape of the mountains. This is bound to attract the attention of scientists engaged in climate modeling. They will need to recalibrate the paleoclimate models around the Himalayas-which may lead to a new theory of paleoclimate in the south of Xizang.

"there are eight laboratories in the world that have the conditions for this kind of analysis." Peggy Chamberlain (Page Chamberlain), professor of Earth and planetary science and senior author of the study. More research can be carried out in the future to reassess the ancient heights of more mountains, such as the Andes and the Sierra Nevada.

References:

Https://www.sciencefocus.com/news/scientists-dont-know-how-himalayas-got-so-tall

Https://www.nature.com/articles/s41561-023-01243-x

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