There exists a theory that, long ago, the entire surface of the Earth was completely frozen.
Yes, there is a possibility that Planet Earth once looked like a giant snowball, drifting through the cosmos.
Rocks can teach us a lot about the history of the planet.
In the late 1800s several discoveries prompted scientists to put forth the idea that, at some point in the past, a global glaciation event took place that covered the entire Earth in snow. Sir Douglas Mawson, a British ex-pat that grew up in Sydney, became interested in glaciations within South Australia's Flinders Ranges.
The geological findings from the region demonstrated extensive glacial sediments, which led him to speculate that the Earth may have undergone a global glaciation event. Although he wasn't the first to put forward the idea, his findings began to solidify the idea that regions far from the poles may have experienced glaciation events in the distant past.
It wasn't until the 1960s that the idea appeared again, when British geologist Walter Harland noticed glacial marine deposits in the Norwegian archipelago, Svalbard. His work continued over the following years and he argued that these deposits had actually occurred at tropical latitudes at some point in the past and thus, there must have been a glaciation occurring closer to the equator.
How could this occur? Modelling techniques first used in 1969 demonstrated that, as long as the sheet ice from polar ice caps extended far enough, the Earth would rapidly cool down due to its increased 'reflectiveness'. Essentially, the giant ice sheets would be huge 'mirrors', reflecting radiation from the sun, resulting in the further cooling and allowing the ice to head further towards the equator.
The 'Snowball Earth' hypothesis wasn't coined until 1992, where work conducted by Joseph Kirschvink, published in The Proterozoic Biosphere, showed the presence of banded iron formations in sedimentary rocks. He went on to speculate that this world-icing even contributed to the Cambrian explosion, when most of the world's major phyla first appear in the fossil record.
It's important to note that the 'Snowball Earth' hypothesis is just that - a theory. Scientists are still trying to reconcile exactly how the planet could come to be wrapped in ice, but research has continued throwing up a variety of reasons for the phenomenon - volcanoes, interstellar dust, oxygenic photosynthesis and evaporite basins. However, modern modelling techniques have failed to adequately show a global glaciation event such as that proposed in the model.
Regardless, the 'Snowball Earth' hypothesis is one that requires a lot more research to completely understand. Understanding these events will help us to better understand global climate change - giving us the ability to combat it before we become a scorched 'Puddle Earth', floating through the cosmos.
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