The "super cold" of the Sinian Period! Was the Earth "frozen" 700 million years ago?

The coldest period on Earth must be the glacial event of the Neoproterozoic Era. The super cold occurred 710-585 million years ago, which is called the Varangian Glacial Period, and in China it is called the Sinian Glacial Period. At that time, the Earth was truly extremely cold, and almost all the oceans were frozen, including near the equator at low latitudes. The continents were covered with ice and snow, and only a small amount of liquid water melted by geothermal heat existed in some parts under the 2km deep ice layer of the ocean. The surface of the Earth was covered with ice and snow, and the cold wind was howling. The sunlight seemed so weak and powerless among the snow particles blown up by the strong wind, without a trace of warmth, as if it was frozen into cold light. The Earth turned into an ice ball - a snowball in the low temperature. Joseph Kirschvinck, a professor of geology at the California Institute of Technology, was the first to call this glacial event the "Snowball Earth" in 1992.

Snowball Earth concept map

Geologists have conducted extensive research on the Snowball Earth event, proposed many hypotheses about its formation and evolution, and found a lot of evidence.

What force has caused the world to become so cold and hot? A representative theory is that as early as 1 billion years ago in the Neoproterozoic Era, the land near the earth's equator gathered together to form the Rodinia supercontinent. 750 million years ago, this supercontinent was split by the stretching of the lithosphere, forming multiple small landmasses, which caused a sudden increase in the land coastline, resulting in an increase in biological photosynthesis and a large amount of weathering of continental silicate rocks. The combined effect of the two is the intensification of CO2 absorption, which causes it to decrease in the atmosphere, the greenhouse effect continues to weaken, and the global temperature drops. As the earth's ice surface increases, the albedo of the ground is enhanced, the earth becomes colder, and the "icehouse effect" dominates the earth. A pure and cold earth wanders in the universe.

Soon after the runaway freeze began, the average global temperature dropped to -50°C. The average thickness of the ice in the frozen oceans exceeded 1 km. Most marine life, invisible to the naked eye, died. How did the cold Earth return to warmth? Volcanic activity helped. After 10 million years of normal volcanic activity, the concentration of carbon dioxide in the atmosphere slowly increased, and the greenhouse effect replaced the icehouse effect again.

Schematic diagram of the formation of Snowball Earth

The red lines are the glacial products of the Snowball period, and above and below are limestone layers formed in the warm ocean.

The greenhouse effect raises the temperature at the equator to the melting point, and the nearby seawater sublimates to produce water vapor, which refreezes at higher altitudes and becomes part of the land glaciers. Finally, the unfrozen water formed in the tropics absorbs more solar energy and begins to increase the global temperature faster. After about 130 million years of ice and snow, the earth has returned to a warm and humid environment.

Eukaryotic organisms - Fungi

The study of Snowball Earth is very important for understanding the evolution of life in the Late Precambrian. Because it was after the Snowball Earth that the evolution of life on Earth achieved a big leap, evolving from simple eukaryotes to metazoans, and multicellular animals appeared for the first time. Perhaps it was the suppression of the evolution of life by Snowball Earth that led to the birth of the Ediacaran fauna and the Cambrian explosion of life, allowing life to achieve a rebound rise of dominant groups.

Author: Biological Evolution and Geohistory Team of the Geological Society of China