How Did Glacial Deposits Form 600 Million Years Ago?Dr. David Pollard, research associate, Penn State College of Earth and Mineral Sciences' Environmental Institute, and James K. Kasting, professor of geosciences at Penn State, believe that glacial deposits that formed on tropical land areas around 600 million years ago could only have formed after the Earth's oceans were entirely covered by thick sea ice. Ice can accumulate in the tropics only if temperatures are below freezing or around freezing with large amounts of snowfall. Tropical glaciers exist today only on high mountain peaks such as the Andes and Mt. Kilimanjaro, and do not reach anywhere near sea level. As the earth cools, the oceans begin freezing. The high reflectivity of the snow and ice that covers the northern and southern oceans reflects, rather than absorbs, the sun's heat and further cools the planet. The researchers conclude that it is unlikely that tropical sea level glacial deposits formed before the collapse into snowball Earth. However, having them form after the oceans freeze also seemed problematic because once the oceans are frozen, the rates of precipitation decrease drastically, to only a few millimeters per year.
Freeze-fry from the snowball EarthOn Dec. 14, Daniel Schrag of Harvard University] presented recent observations in favor of the snowball Earth at the American Geophysical Union’s meeting in San Francisco, which lasted from Dec. 12–17...
by Christina Reed
But some scientists still remain skeptical. During a presentation at the AGU meeting, Gregory Jenkins of Pennsylvania State University supported what is called the high obliquity hypothesis over the snowball Earth hypothesis. Jenkins argued that climatic conditions during the Neoproterozoic resulted from a severe tilt of Earth on its axis, possibly caused by the impact of the planetoid that formed the moon. Although a tilted Earth may have cooled the equator and warmed the poles, the theory is still hotly debated as an explanation because it seems to require low-latitude cooling prior to Neoproterozoic glacial events.
Schrag and others defend the snowball Earth theory, saying it brings context to mysteries that have plagued the geological community for decades. It explains how glaciers survived in the tropics, how iron-rich rock emerged in an oxygen-enriched world and how warm-water carbonate rocks found themselves perched atop glacial deposits. It may even explain the explosion of life in the Cambrian.
[P]aleomagnetism specialist Joe Kirschvink of Caltech linked the effect a frozen Earth would have on the hydrological cycle to a buildup of volcanic carbon dioxide. If ice covered the oceans to the equator, it would block off evaporation, dry up the clouds and deny water the chance to erode the land. Carbon dioxide would build up in the atmosphere instead of being washed out by rain and carried back to the oceans as carbonates from land. With enough carbon dioxide, the "snowball Earth" would then become a hothouse, Kirschvink said in a 1992 paper published in the book The Proterozoic Biosphere.
In 1992, Kenneth Caldeira of Lawrence Livermore National Laboratory and James F. Kasting of Pennsylvania State University calculated that the amount of carbon dioxide needed to reverse the snowball effect would be 350 times present-day levels. With a global average of 50°C below zero, Earth would bake under extreme global warming to 40–50°C in only a few thousand years.
This is a TREMENDOUS discovery, and thanks for adding some links to "snowball Earth"/ Continental Drift stories.
Greenland being "old" does not surprise me. That Greenland has been able to preserve 3.8Byo material is astonishing!
The "Professor Moores" mentioned in this article is a pioneer in this field and is well respected. Congratulations to him and his team!