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

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

Before the Marino ice age, there was the evolution of life on earth, and eukaryotes such as cyanobacteria dominated the earth. So, during this "snowball Earth" incident, is the earth really in a state of global ice, and how do living things survive and evolve in the long cold?

Wen Jing | Wen Jing

The team of Professor Tong Jinnan of China University of Geosciences (Wuhan) published their research results in the journal Nature Communication, introducing a new "snowball earth" model, that is, 635 million years ago, open seas existed in both middle and low latitudes. This model provides a new understanding of how organisms survive and evolve in the "Snowball Earth" period, and modifies the evolution map of life in that period.

In the 600-700 million years ago, two extremely long and severe extreme cold events occurred on the earth, namely the Sturtian ice age and the Marino ice age in the Neoproterozoic. In these two events, the earth's surface ice sheet rapidly expanded to the equator at low latitudes, forming a global ice situation that lasted for tens of millions of years. This is the famous "Snowball Earth" period.

Photo Source: unsplash at present, there is still a lot of controversy about the model and cause of formation of Snowball Earth in academic circles, and there are mainly two mainstream academic viewpoints: one is that during the period of Snowball Earth, there may be ice cones or ice holes on the surface of the low-latitude ice sheet; the other is that "Snowball Earth" is not global ice, and there are open waters in low-latitude equatorial regions, that is, the "Snow Ball Earth" theory.

"however, neither of these hypotheses can well explain the key scientific issue of how organisms survived and evolved during the Snowball Earth period." Tong Jinnan said.

By studying the "Songluo biota" of the Nantuo formation in the Songluo section of the Songluo section in Shennongjia area, South China, Tong Jinnan team provided a great deal of paleontological and geochemical evidence and inferred that the livable open sea area at that time was more extensive than previously thought. extended to the mid-latitude coastal oceans and provided refuge for eukaryotes during the biomass decline phase of the Marino Ice Age.

There is a "snowball earth" model of open sea in both middle and low latitudes. Photo source: how did the ice age occur on Nature Communication's official website? Some studies believe that the occurrence of many ice ages in geological history is due to exuberant photosynthesis. At first, the amount of carbon dioxide in the atmosphere decreased only slightly, but with the reduction of greenhouse gases in the atmosphere, the heat preservation effect of the atmosphere on the earth's surface decreased. At the same time, the area of the ice sheet expands and the reflection of sunlight is enhanced, which further accelerates the decline of temperature.

Under this positive feedback mechanism, the surface is finally unable to obtain and utilize the energy of the sun, and there is a "snowball earth" period that lasts for tens of millions of years. The elimination of this positive feedback usually requires the release of heat and greenhouse gases such as carbon dioxide from the interior of the earth, that is, volcanic eruptions, earthquakes and so on.

Photo Source: pixabay, corresponding to this, there are many "extreme heat events" in history. For example, a rise in greenhouse gases such as carbon dioxide in the atmosphere will lead to a rise in temperature, and once this incentive breaks through a critical value and triggers a positive feedback mechanism, it will bring disaster to life on Earth. The recovery of the "extreme thermal event" is also the result of the coupling of the carbon cycle and climate. For example, Azolla, a floating plant with "cooling and carbon sequestration", led the earth to recover from the "Paleocene-Eocene extreme thermal event".

The study of "extreme heat events" in history can provide guidance for alleviating the current climate problems faced by mankind, because the earth is now in an "interglacial period" with rising temperatures.

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