Snowball Earth Rare Rock Specimen
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 were that tropical glacial deposits have been found in equatorial paleoaltitudes along with "dropstones" carried by glaciers. There is 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." It would be difficult for the Earth to unlock such a grip from ice, as ice reflects sunlight and that would mean there would never be a way to break such a hold. There are a few ways to do so, in spite of the reflectivity of ice. Earth's axis could "wobble" long enough to allow for a prolongation of the sun's heat in more concentrated areas.
Plate tectonics could begin and effectively nurture geological activities including volcanic action and mountain upthrusts. A third way would be that there was some external bombardment of the atmosphere with meteorites and comets creating yet another mechanism for heating the atmosphere if the sun was still too weak. Or lastly, the sun effectively got better at shining and producing more radiant heat.
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 (4567 Ga). 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 is 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 its history. We would not be here had it not occurred. It has been proposed that rise of free oxygen that occurred during the Great Oxygenation Event removed methane in the atmosphere through oxidation. As the Sun is thought to have been weaker at the time and Earth's climate probably relied on methane, a powerful greenhouse gas, to maintain marginal surface temperatures.
The second snowball earth occurred around 710 Ma and like the Marinoan (see described below) its 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. No suitable material has yet been found to date the initiation of the Marinoan snowball earth, but it must have occurred after ~663 Ma. This intense weathering led 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 (large soft-bodied modular organisms unassignable to extant phyla) 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. Our young sun 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.
The Kaigas "glaciation" was probably a major cooling event but it was not global in extent, like the aforementioned Snowball Earth events. It is believed that tectonic motion first began on our planet around three billion years ago, and what part it played in the grand design of saving us from the grips of the different Snowball Earth events is not at all well understood.
The three proposed Snowball Earth events are thought to have occurred before the sudden onset of multicellular bioforms, known as the Cambrian explosion. Their participation in helping in the development and being a necessary mechanism in the evolution of life on Earth is debated. There are certainly some interesting parallels in Earth's timeline between the Snowball Earth events and emerging life forms.
About the specimen: This specimen was recovered from the Espanola Formation, a part of the Huronian Supergroup of Canada, a period from 2.22 Ga to 2.21 Ga. This supergroup contains capstone carbonate with dating associated to the time of the very first known Snowball Earth. Analysis does indicate a negative carbon isotope anomaly in response to environmental changes to global glaciation in this material. The Huronian glaciation (or Makganyene glaciation) was a glaciation that extended from 2.4 billion years ago (Ga) to 2.1 Ga. The Huronian glaciation followed the Great Oxygenation Event (2.45 Ga), a time when increased atmospheric oxygen decreased atmospheric methane. (The oxygen combined with the methane to form carbon dioxide and water, which do not retain heat as well as methane).
Specimen size: 63mm H X 48mm W X 43mm" D
Here is one of only a very few opportunities to obtain for your unique geological collection an extremely rare and exceptional specimen from one of Earth's earliest major geological events.
Ships in a specimen display box with information, tag and Certificate of Authenticity. Stands and cube not included.
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