The History of Our Planet: Snowball Earth
Imagine for a couple of seconds that our precious home — the Earth is completely encased in the snow; its oceans, seas, and rivers are frozen; cold is everywhere. It’s hard, isn’t it? However, it is assumed, that there was a period in the history of our home, where the whole territory of the planet was buried under the glaciers.
The evidence for this hypothesis was found across multiple continents, scientists say these Snowball Earth events may have paved the way for the Cambrian explosion of life that followed — the period when complex, multicellular organisms began to diversify and spread across the planet.
According to the study, paleomagnetic evidence suggests that the ice line reached sea level close to the equator. Geologist Joe Kirschvink proposed a snowball Earth, created by a runaway albedo effect feedback, in which the ocean was covered by sea ice; however, the continental ice cover was thin and patchy because of the virtual elimination of the hydrologic cycle.
But what was the reason for this dramatic glaciation? Why did it happen?
Scientists have been studying this question for a long period of time. They think that the glaciation could be connected with the volcanic activity that had been happening before this event.
Volcanism is a natural process, where, during the eruption, the greenhouse gas (CO2) emits into the atmosphere and can lead to serious consequences.
What made Earth a snowball was the nature of volcanic explosions. They lasted thousands or even millions of years.
When continental landmasses 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,” explains Prof. Schmitt.
So, the main reason for this severe glaciation was the high reflectivity, or albedo, of ice. Ice reflects 55 to 80 percent of incoming sunlight, sending that energy back into space before it can warm the planet. By comparison, ocean water reflects just 12 percent, and land areas reflect between 10 and 40 percent, so more of the sun’s heat is absorbed by these surface conditions. An additional factor in cooling the planet is that the Sun was 6 percent fainter during the Cryogenian period than it is now.
SNOWBALL OR NOT?
However, the thaw of the Snowball Earth hasn’t been properly explained.
One of the reasons could be a volcanic activity releasing a huge amount of carbon dioxide into the air and warming the planet.
“There is no geologic evidence to support that much CO2 in the Cryogenian atmosphere”, said Linda Sohl, geologist of Columbia University’s Center for Climate Research and NASA’s Goddard Institute for Space Studies.
Another problem for the hard snowball theory is the lack of a massive extinction event in the Cryogenian fossil record. Despite the colossal glaciation where the sunlight should be reflected by ice causing further cooling of the planet, only relatively small extinctions have been found.
“The suggestion that the Earth was once entirely covered by ice — the continents by thick ice sheets and the oceans by thick sea ice — remains somewhat contentious,” said physicist of the University of Toronto Richard Peltier.
As a result of these discussions and concerns a “Slushball Earth” theory has been developed, according to which, most of the Earth was covered by ice, but open water remained near the equator. However, scientists don’t deny the possible existence of the snowball Earth periods.
