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The Snowball Earth, also known as the Varangian glaciation, is a recent hypothesis, largely formulated by Paul F. Hoffman , Sturgis Hooper Professor of Geology at Harvard University. It proposes that the ice age which took place in the Precambrian was so severe that the Earth's oceans froze over completely, with only heat from the planetary core causing some liquid water to exist under ice more than a kilometer thick. More recent work suggests that the oceans would have remained liquid at the surface in the tropics.1 Overview
Since the 1960s, it has been known that the Earth's continents were subjected to glacial action between about 750 million and 580 million years ago. Paleontologist W. Brian Harland pointed out that contemporary glacial till deposits can be found on all continents, and first proposed that the Earth must have been in an ice age at this time. The problem is that they are found on all continents; even during the worst of the ice age just past, ice was still uncommon in equatorial continents. At first the then-new theory of plate tectonics seemed to offer an out, but in fact made the situation worse: studies of the magnetic orientations of the rocks of the period showed that the continents were clustered around the equator, as the supercontinent Rodinia, rather than being near the poles as might have been hoped.
The Snowball Earth theory argues backwards from the documented existence of tillite s dropped by these glaciers, to suggest that the Earth must have frozen over. The mechanism by which it did so is still mysterious, but one suggestion is that the presence of the at-first ice free continents at the poles enhanced the natural process of carbon dioxideCarbon dioxide is an atmospheric gas composed of one carbon and two oxygen atoms. One of the best known of chemical compounds, it is frequently called by its formula: :CO (pronunciation: "see oh two") Carbon dioxide results from the combustion of organic reabsorption through the erosion of silicate rocks, reducing the greenhouse effectThe greenhouse effect is the process by which an atmosphere warms a planet. Mars, Venus and other celestial bodies with atmospheres (such as Titan) have greenhouse effects, but for simplicity the rest of this article will refer to the case of Earth. The t and making the Earth colder until it reached a runaway point. However, the mechanism by which the Earth would unfreeze (as it has to have done if it did freeze at one point in the past) would leave distinctive traces.
2 Evidence
Geological formations which "Snowball Earth" proponents point to as evidence of the hypothesis are ironThis article is about metallic iron. For the ironing device, see ironing manganese iron cobalt Fe Ru Full table General Name, Symbol, Number iron, Fe, 26 Chemical series transition metal Group, Period, Block 8 (VIIIB), 4 , d Density, Hardness 7874 kg/m3,-rich rocks and carbonateCarbonate is an anion with a charge of -2 and an empirical formula of CO2-. An aqueous solution of carbon dioxide contains a minute amount of HCO, called carbonic acid, which dissociates to form hydrogen ions and carbonate ions. It would be a fairly stron cap rocks. The association of the Snowball Earth event with the Cambrian Explosion is also of interest.
2.1 No Plants
There are two forms of carbon in sea waterSea water is water from a sea or ocean. On average, sea water in the world's oceans has a salinity of ~3. This means that for every 1 liter (1000mL) of sea water there are 35 grams of salts (mostly, but not entirely, sodium chloride) dissolved in it.: carbon-12Carbon 12 is a stable isotope of the element carbon. It is referenced in the definition of the SI base unit mol . Carbon-11 Isotopes of Carbon Carbon-13 Produced from Nitrogen-12 Boron-12 Decay chain Does not decay See also Carbon Carbon-14 isotope Mole ( and carbon-13Carbon-13 is a stable isotope of carbon. It makes up about 1. 11% of all naturally-occurring carbon on earth. Carbon-12 Isotopes of Carbon Carbon-14 Produced from Nitrogen-13 Boron-13 Decay chain Does not decay See also Carbon isotope Chemical isotope.. Ocean dwelling plants prefer carbon-12, so an ocean with plant life would have some carbonate rocks with carbon-13, while carbonate rocks in a dead ocean would have more carbon-12. During the supposed time of Snowball earth, there seemed to be no plant life in the water, which suggests a deep freeze killing off plant life in the water.
