How did the Snowball Earth hypothesis get started?
This theory was originally based on paleomagnetic studies. It was thought that the entirety of the Earth was frozen over from pole to pole, all the way solid to the equator. The indications for a Snowball Earth were that tropical glacial deposits have been found in equatorial paleoaltitudes along with "dropstones" carried by glaciers, discovered in various places. There has been some debate about whether the Earth was entirely locked in ice or if there were intermittent patches of open water, or maybe even something more akin to a "slush-ball."
So, when did Snowball Earth occur and were there others? The oldest and first discovered Snowball Earth dates back to ~2200 Ga, about nearly half the age of the Earth. It is believed to represent a Snowball Earth because paleomagnetic evidence of Earth's past magnetic field had been "fossilized" in rock and suggests that these glacial indicators were deposited close to the equator. It came to be known as the Makganyene Snowball Earth and afterwards, has been broadly associated in time with the rise of "free" oxygen, molecular O2, the most profound revolution of the Earth's surface (atmosphere, oceans, crust and life) in the entirety of it's history. We would not be here had it not occurred.
The second Snowball Earth occurred around 710 Ma and like the Marinoan it's sedimentary deposits have been found on virtually every continent. It is commonly referred to as "Sturtian Snowball Earth," after the Sturtian glacial sediments in South Australia, first described in 1908 by the geologist Walter Howchin. Great attention has been drawn to these deposits because they contain large sedimentary iron deposits ("banded iron formation", or BIF) in different areas. Neither the initiation nor termination of the Sturtian Snowball Earth has been conclusively dated, although some evidence suggests that it lasted for millions of years.
The last and third Snowball Earth ended 635 million years ago (Ma), near the end of the Proterozoic Eon. For reference, the oldest bilaterian animal fossils (555 Ma in Arctic Russia) are 80 million years younger. This Snowball Earth is often referred to as "Marinoan Snowball Earth," after glacial sediments in South Australia described in 1949 by the geologist and famed Antarctic explorer, Sir Douglas Mawson. Sedimentary deposits from this glaciation are found on virtually all continents, and were recognized in Arctic Norway as long ago as 1891 by the geologist Hans Reusch. It has been estimated in different ways that the Marinoan snowball earth could have lasted for 6-12 million years, but scientists aren't completely sure. Intense weathering leads to the development of cap carbonates, a characteristic layer of rocks that form when calcium carbonate – chalk – falls out of solution in water. Chemical analysis of some of these rocks in southern China act as direct evidence for the intense chemical weathering that could have brought an end to this snowball earth. Similar deposits on the island of Newfoundland, Canada, have been dated near 580 Ma, 55 million years after the Marinoan snowball earth ended. Note that the Ediacaran Period 635–541 million years ago the first fossils beds of Ediacara evolved.
It has been thought that a build-up of carbon dioxide and other greenhouse gases from volcanic activity drove the period of melting, and in essence saved our planet from many icy grips. As our young sun developed, it had a growing ability for heating our planet as well. High levels of carbon dioxide in the atmosphere led to very acidic rain. This would have washed over the continents in storms and left chemical signatures in the surface rocks.
About the specimen: This specimen was recovered among the glacial till in the Espanola Formation, a part of the Huronian Supergroup of Canada, and is dated to a period from 2.2 Ga to 2.21 Ga. This supergroup contains capstone carbonates. Capstone carbonates can form in deep methane sinks and can also be found in warm oceans. Being that both glacial till and cap carbonates were found together lends credibility to the theory that during this time the Earth was entirely covered in ice, especially with dating associated to the time of the very first known Snowball Earth.
Specimen size: 68mm H X 48mm W X 12mm D
This is a very unique opportunity to obtain an extremely rare and interesting specimen from one of Earth's major geological events.
Ships in a specimen display box with information, tag, tag stand and Certificate of Authenticity. Acrylic base and cube not included.
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