The Undeniable Evidence Supporting the Snowball Earth Theory
Present-day conditions on Earth make it quite difficult for many people to believe
that at one point the entire globe was covered with ice. There is a hypothesis, known as
the Snowball Earth theory, which suggests this event actually once happened. The theory
is both supported and declined by scientists across the globe. While evidence such as
geothermal heat activity, sedimentological and stratigraphic data and carbon isotopic
signatures act to dismiss the theory, there is more compelling evidence such as iridium
deposits, lower amounts of Neoproterozoic Sun radiation and the workings of the ice
albedo feedback system, all strongly support the theory.
The Snowball Earth theory encompasses the idea that at one point the entire globe
was completely covered by ice- whether that meant continental ice or sea ice. About 600
million years ago, during a time period called the Neoproterozoic, a massive ice advance
swept the globe and reached as far as the tropics (Hoffman & Schrag, 2000). This meant
there a layer of ice would separate atmosphere and water, making diffusion of gases
between the atmosphere and water nonexistent (Allen & Etienne, 2008). Paleomagnetic
evidence actually suggests that the global ice line advanced to the equator at least twice
in Earth’s history (Hoffman, Kaufman, Halverson & Schrag, 1998). One of these times is
believed to have been during the Snowball Earth phase. Glacial debris can be found in the
tropics, which also suggests that at one time glaciers were present in the lower latitudes
(Hoffman & Schrag, 2000). In order for the Snowball Earth theory to be proven however,
evidence would need to suggest full ice coverage, not just suggest the presence of
glaciers in the equatorial regions.
Some scientists do not believe that the Earth experienced a full on freezing event.
They believe the Earth experienced a “Slushball Earth” event, which characterizes a
period in time where majority of the Earth was covered in glaciers, except for the open
tropical oceans (Kerr, 2005). Geothermal heat is constantly radiating from the Earth’s
core, and seeps between openings in the tectonic plates (Hoffman & Schrag, 2000). When
it rises to the surface of the Earth, it helps to heat the surface. We see this occurring
today, and evidence suggests the heat coming from the Earth’s core was greater in the
past (Hoffman & Schrag, 2000). This could have prevented a full freezing event of the
oceans.
Sedimentological and stratigraphic data suggests that although ice was present
throughout the low latitudes, some of the Earth’s oceans were ice-free, thus allowing
exchange of gases between water and the atmosphere (Allen & Etienne, 2008). This is
important because this means free movement of carbon dioxide and methane, both
greenhouse gases, would have occurred. Many scientists believe marine life could not
survive without some amount of free movement of gases between the atmosphere and
ocean, because levels would have built up in the ocean to a fatal level. A full covering of
ice would also mean sunlight could not penetrate into the water, preventing
photosynthesis (Vincent & Howard-Williams, 2000). It is then assumed that a full
freezing over of oceans would have likely exterminated all life, yet there are signs that
microscopic algae known as cyanobacteria was able to survive in large quantities
(Hoffman & Schrag, 2000). The carbon isotopic signature found in rocks worldwide
suggests a prolonged drop in biological productivity (Hoffman & Schrag, 2000).
Although microscopic cyanobacteria were able survive the Neoproterozoic ice
advance, this does not necessarily mean there full ice coverage was not present. It is
important to remember that these organisms are able to survive in very extreme
environments, and could have survived off carbon dioxide deposits at the depths of
oceans (Cavalier-Smith, 2013). While carbon isotopic signatures show there was a
significant drop in biological life during the time of this glacial advance, this corresponds
with the idea that an event as large as the Snowball Earth would have large impacts on
biota. Although not all biota perished, the only biota that survived this period were the
organisms that are able to endure extremely harsh conditions. It is important to recognize
that biologically diverse systems are presently able to survive in the Arctic and Antarctic,
which are areas of continuously vast ice coverage (Vincent & Clive Howard-Williams,
2000). In fact, large communities of cyanobacteria are commonly found in Earth’s polar
regions (Vincent & Howard-Williams, 2000). This makes it possible that cyanobacteria
could have survived even if the oceans were covered by ice.
Solar effects had, and continue to have, an influence on the Earth and its climate.
A naturally occurring element known as iridium continuously falls onto Earth from space
(Kerr, 2005). An unusually large quantity of iridium was found in deposits aging about
635 million years ago (Kerr, 2005). In order to obtain such an irregularly large sample of
iridium, the globe had to have been frozen in place for a large time period. If the Earth
were not solid ice, regular deposits of iridium would have been deposited in various
thinner deposits. Instead, one thick-banded deposit was found, as if the Earth had been
held at a frozen state for some period of time.
It is suggested that the Neoproterozoic Sun was about six percent weaker than the
Sun is today, meaning less incoming solar radiation reached Earth (Hoffman & Schrag,
2000). This could have lead to a globe covered in ice, as the temperature would have
been colder than current average temperatures. When considering the ice albedo feedback
process, it is important to note that any ice formed at latitudes lower than 30 degrees from
the equator will increase the planet's albedo (Hoffman & Schrag, 2000). This is because
more direct sunlight would be striking a larger surface area of ice, creating higher levels
of reflection (Hoffman & Schrag, 2000). It has already been mentioned that evidence
suggests ice was present at these low latitudes, which would have extenuated the freezing
of oceans. This creates an increasing domino effect of ice formation in equatorial areas.
The full extent of global ice coverage is constantly debated among the scientific
community. Because of how long ago this event occurred, decisions must be based purely
on collections of evidence. Given the fact that there was higher geothermal heat levels,
both sedimentological and stratigraphic data suggest only partial ice coverage, and the
carbon isotopic signatures from the past all disprove the theory, evidence such as
unusually large iridium deposits, minimal Neoproterozoic Sun radiation and the ice
albedo feedback system, are concepts which are much more convincing. A world that is
covered in ice may be a hard concept to grasp; yet it is fully plausible.
References
Allen, P. A. & Etienne, J. L. (2008). Sedimentary challenge to Snowball Earth. Nature
Geoscience, 1, 817-825. Retrieved on February 13, 2014 from
from http://www.nature.com.proxy2.lib.umanitoba.ca/ngeo/journal/v1/n12/full/nge
o355.html
Cavalier-Smith, T. (2013). Early evolution of eukaryote feeding modes, cell structural
diversity, and classification of the protozoan phyla Loukozoa, Sulcozoa, and
Choanozoa. European Journal of Protistology, 49, 115-178. Retrieved on February
13, 2014 from http://ac.elscdn.com.proxy2.lib.umanitoba.ca/S0932473912000508/1-s2.0S0932473912000508-main.pdf?_tid=2c1b2662-953d-11e3-98e900000aacb361&acdnat=1392357751_6e149d21734ac28f5f48620542890a3e
Hoffman, P.F., Kaufman, A. J., Halverson, G. P. & Schrag, D. P. (1998). A
Neoproterozoic Snowball Earth. Science. 281, 1342-1346. Retrieved on February
10, 2014 from http://www.jstor.org/stable/2896437
Hoffman, P. F. & Schrag, D. P (2000). Snowball Earth. Scientific American, 282, 68-75.
Retrieved on February 10, 2014 from
http://www.nature.com.proxy2.lib.umanitoba.ca/scientificamerican/journal/v282/n1
/full/scientificamerican0100-68.html. doi: 10.1038/scientificamerican0100-68
Kerr, R. A. (2005). Cosmic dust supports a snowball Earth. Science, 308, 181. Retrieved
on February 11, 2014 from
http://www.sciencemag.org.proxy2.lib.umanitoba.ca/content/308/5719/181.full.pdf
?sid=56a9c002-d7b4-4d5e-baa9-e379c334b8c9
Vincent, W. F. & Howard-Williams, C. (2000). Life on Snowball Earth. Science.
Retrieved on February 12, 2014 from
http://find.galegroup.com.proxy2.lib.umanitoba.ca/grnr/infomark.do?&source=gale
&idigest=68467e991fa0632b62bccf5d2ccaf97b&prodId=GRNR&userGroupName
=univmanitoba&tabID=T002&docId=A61793493&type=retrieve&contentSet=IAC
-Documents&version=1.0