snowball earth

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snowball earth,

hypothesized condition in which the earth was covered completely by ice during several periods in the Proterozoic. The hypothesis was originally developed to explain evidence of the contribution of glaciation to the formation of siltstone whose layered structure and paleomagnetic composition indicated that its sediments were most likely deposited at sea level in the tropics. In the most extreme form of the hypothesis, glaciation that reached within 30° of the equator (a subtropical latitude) resulted in the reflection of so much sunlight that the earth cooled sufficiently to allow ice sheets to reach the equator, where temperatures were similar to those of present-day Antarctica; the ice sheets completely covered the earth for tens of millions of years. Many proponents of the theory support a slushball earth hypothesis in which glaciation reaches into the tropics but is not complete. The snowball earth hypothesis is controversial. Many critics have questioned if a snowball earth condition would be reversible, and if early life could have survived such extreme conditions. The long-term accumulation of very high levels of carbon dioxide in the atmosphere from volcanic eruptions is generally proposed as the cause of the ice sheets' retreat, and it has been suggested that specialized environments, such as hydrothermal ventshydrothermal vent,
crack along a rift or ridge in the deep ocean floor that spews out water heated to high temperatures by the magma under the earth's crust. Some vents are in areas of seafloor spreading, and in some locations water temperatures above 350°C; (660°F;) have
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, could have enabled life to survive. Despite these disagreements, there is evidence for glaciation several times during the Proterozoic; the Marinoan (650 to 635 million years ago) and Sturtian (750 to 700 million years ago) glaciations are generally considered to be the times when snowball or slushball earth conditions most likely existed.
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Snowball Earth morphed into hothouse Earth and back again, with an assist from the steady march of plate tectonics across the surface of the globe.
That spike corresponds to a period known as snowball earth.
The creatures may have evolved in the warming period between the Cryogenian's two snowball Earth events.
Snowball Earth uncovers the story behind one of the most controversial theories today.
In her second popular science work after Snowball Earth (2003), she examines the Earth's atmosphere and some of the people who have explored and used their knowledge of it over the centuries.
The crisis referred to "the time known as Snowball Earth - because the whole planet would have appeared as an icy ball".
In Rotorua, New Zealand, he shows how volcanoes have played a critical role in keeping the planet habitable by providing a natural form of global warming, and how they saved the planet from one of the greatest disasters it has ever faced - called Snowball Earth.
Although Gabrielle Walker, author of Snowball Earth (2003), holds a Cambridge doctorate in chemistry, her ear for storytelling is perfect for popular science.
In fact, the researcher concludes, "The changing galactic environment of the solar system has had dramatic consequences, including Snowball Earth episodes.
A fantasy, aboriginal myth-based, time-travel story, Snowball Earth finds a boy (Gabe) and a girl (Allie) battling Aurgel, the Ice Spirit, from beginning an ice-age.
The Snowball Earth hypothesis is the subject of considerable media interest on a par with global warming.
1: Dan Schrag, Earth and Planetary Sciences at Harvard University, "A Neoproterozoic Snowball Earth.