Snowball Earth Hypothesis
When Caltech geologist Joe Kirschvink coined the term Snowball Earth in 1989 — merging
ideas that some geologists, climate physicists and planetary chemists had been thinking
about for decades many earth scientists were sceptical that these cataclysmic events could
really have occurred.
The evidence for this hypothesis is found in old rocks that preserved signs of Earth’s
ancient magnetic field. Measurements of these rocks indicate that rocks known to be
associated with the presence of ice were formed near the Equator.
In addition, there is a 45-metre- (147.6-foot-) thick layer of manganese ore in the Kalahari
Desert with an age corresponding to the end of the 2.4 billion-year “Snowball Earth” period;
its deposition is thought to have been caused by rapid and massive changes in
global climate as the worldwide covering of ice melted.
Geologists were struggling to understand what they saw in the geologic record — that not
too long before the first appearance of complex life, there was unmistakable evidence of
glaciation even in the warmest areas of the Earth. Geologists had a very difficult time
understanding how this was possible.
The biggest problem was that because the conditions were so different from any other time
in Earth’s history.
Geochemical and sedimentary evidence indicates that Earth experienced as many as four
extreme cooling events between 750 million and 580 million years ago.
Extreme volcanic outpourings resulting in so-called large igneous provinces could be
responsible for these Snowball Earth global glaciations. When continental land masses break
up, it causes a volcanic binge that also releases massive amounts of CO2 into the atmosphere,
which can cause short-term global warming.
Then, however, the lava rock begins to weather. "The weathering process is especially
intense at tropical latitudes. Over timescales of millions to tens of millions of years, the
weathered rocks can sequester sufficient carbon dioxide to plunge Earth's climate into an
extreme ice age.
A tropical distribution of the continents is, perhaps counter-intuitively, necessary to allow
the initiation of a snowball Earth. Firstly, tropical continents are more reflective than open
ocean, and so absorb less of the Sun's heat: most absorption of Solar energy on Earth today
occurs in tropical oceans.
Global temperature fell so low that the equator was as cold as modern-day Antarctica. This
low temperature was maintained by the high albedo of the ice sheets, which reflected most
incoming solar energy into space. A lack of heat-retaining clouds, caused by water vapor
freezing out of the atmosphere, amplified this effect.
When Caltech geologist Joe Kirschvink coined the term Snowball Earth in 1989 — merging
ideas that some geologists, climate physicists and planetary chemists had been thinking
about for decades many earth scientists were sceptical that these cataclysmic events could
really have occurred.
The evidence for this hypothesis is found in old rocks that preserved signs of Earth’s
ancient magnetic field. Measurements of these rocks indicate that rocks known to be
associated with the presence of ice were formed near the Equator.
In addition, there is a 45-metre- (147.6-foot-) thick layer of manganese ore in the Kalahari
Desert with an age corresponding to the end of the 2.4 billion-year “Snowball Earth” period;
its deposition is thought to have been caused by rapid and massive changes in
global climate as the worldwide covering of ice melted.
Geologists were struggling to understand what they saw in the geologic record — that not
too long before the first appearance of complex life, there was unmistakable evidence of
glaciation even in the warmest areas of the Earth. Geologists had a very difficult time
understanding how this was possible.
The biggest problem was that because the conditions were so different from any other time
in Earth’s history.
Geochemical and sedimentary evidence indicates that Earth experienced as many as four
extreme cooling events between 750 million and 580 million years ago.
Extreme volcanic outpourings resulting in so-called large igneous provinces could be
responsible for these Snowball Earth global glaciations. When continental land masses break
up, it causes a volcanic binge that also releases massive amounts of CO2 into the atmosphere,
which can cause short-term global warming.
Then, however, the lava rock begins to weather. "The weathering process is especially
intense at tropical latitudes. Over timescales of millions to tens of millions of years, the
weathered rocks can sequester sufficient carbon dioxide to plunge Earth's climate into an
extreme ice age.
A tropical distribution of the continents is, perhaps counter-intuitively, necessary to allow
the initiation of a snowball Earth. Firstly, tropical continents are more reflective than open
ocean, and so absorb less of the Sun's heat: most absorption of Solar energy on Earth today
occurs in tropical oceans.
Global temperature fell so low that the equator was as cold as modern-day Antarctica. This
low temperature was maintained by the high albedo of the ice sheets, which reflected most
incoming solar energy into space. A lack of heat-retaining clouds, caused by water vapor
freezing out of the atmosphere, amplified this effect.
