The theory of Snowball Earth suggests that the Earth experienced periods of extreme cold during the Proterozoic Eon, resulting in a global ice age.
Imagine a completely snow-covered Earth. Everywhere you look, there are vast ice oceans. It’s not just the mountains, even the land is white, and the glaciers extend all the way to the tropics.
These periods in the history of our planet were truly remarkable.
It was a very different time from today. All the continents were located around the equator, and life only existed deep in the oceans. Sometime between 540 million and 2.5 billion years ago (during the Proterozoic Eon), the Earth experienced global glaciation events, becoming almost frozen like a “snowball”. Evidence suggests that the Snowball Earth Event occurred more than twice in the geological past.
A picture showing a frozen Snowball Earth without surface water (Photo Credit: 3depix/Wikimedia Commons)
How can a planet freeze?
This question can be answered by considering a well-known climatic phenomenon called the Albedo-feedback loop. Albedo is a scientific term that refers to the reflective properties of a surface. It means that a surface with a high albedo will reflect most of the sunlight that falls on it.
Ice and snow have a high albedo, reflecting about 90 percent of the radiation that falls on them, while dark oceans and land have a low albedo and absorb much of the energy. The albedo feedback mechanism is sensitive to minor variations, which can cause the land to rapidly transition from ice-free to frozen and back to ice-free.
The Ice Albedo Feedback effect, where solid ice reflects most of the sunlight falling on it
So what caused the planet to freeze?
Imagine that the Earth undergoes a sudden cooling event (perhaps due to a decrease in the amount of sunlight reaching the surface or a rapid drop in CO2 levels). This triggers the formation of massive ice glaciers. It’s also important to remember that during prehistoric times, complex multicellular organisms did not exist to regulate the amount of carbon in the atmosphere.
The Earth would enter a severe albedo feedback cycle, covering the land with ice from the poles to the equator. It would remain in this state for many years.
How did the Earth recover from the snowball state?
Certain natural processes proved to be beneficial for the flourishing of life on Earth. Over an extended period, plate tectonics and volcanoes may have released enough greenhouse emissions to start warming the planet again. As more surface area was exposed, another runaway albedo feedback mechanism would have started, causing the ice to melt rapidly until it completely disappeared.
Volcanic eruptions emitting greenhouse gases (Photo Credit: Eva Kali/Shutterstock)
Huge amounts of methane were released from the carbon trapped in ice sheets on the ocean floor, further driving global warming. With hot tropics and freezing poles, the Earth stabilized once again.
What Evidence Supports the Snowball Earth Hypothesis?
Geologists have found evidence of glacial deposits occurring between limestones in various locations worldwide. Normally, limestones are formed in shallow water in tropical or subtropical regions, while glaciers do not exist at sea level near the tropics. So, what could have caused these unique formations?
Researchers have been convinced by the data obtained from paleomagnetic signatures, which study the strength and direction of the magnetic field in ancient rocks. This data suggests that these formations are tropical and were deposited at sea level.
Black Band Ironstone (Photo Credit : Aka/Wikimedia Commons)
Another significant piece of evidence is the presence of Banded Iron Formations (BIFs) during the Snowball Earth periods. This could occur if the land and oceans were covered in ice, as it would make the water acidic and rich in dissolved carbonates. The freezing of rivers would cut off the supply of sulfate to the seas. In such acidic, oxygen-free, low-sulfur waters, a large amount of dissolved iron would accumulate and settle at the bottom of the ocean, forming BIFs.
Snowball or Slushball Earth?
Although there is sufficient data to support the Snowball Earth theory among geologists, some researchers hold a different view. They argue that the entire tropical region did not freeze completely and should not be referred to as a snowball. Instead, they propose a less extreme concept called the “slushball” model.
The slushball model suggests that there was glaciation on the equator-side, but most of the tropical area remained ice-free. Sedimentary data that could only have formed in water, not ice, supports this idea. However, this counterpoint is not new, as even the initial “snowball” model allowed for certain ice-free areas in the tropical regions.
Will the Earth Experience Another Snowball Event?
Scientists have linked glaciation events to a sudden decrease in the amount of solar radiation reaching the Earth’s surface over a short period of time.
The processes that may have caused the atmosphere to darken over millions of years are still unclear. One explanation is that multiple volcanic eruptions released smoke into the atmosphere, blocking sunlight from reaching the planet.
Another possibility is that early algae developed mechanisms that created clouds and reflected light. Whatever the cause, it resulted in abrupt fluctuations in solar energy.
Anthropogenic Warming can induce climatic disasters. Let’s save ourselves by making wiser and more conscious choices. (Photo Credit : VectorMine/Shutterstock)
Although the current climate trend suggests that humans will not cause a Snowball Earth event, we need to be aware of critical tipping points caused by changes in environmental phenomena. We must consider the pace at which we are altering the Earth’s environment, not just the measurable amounts. Human activities can also influence the rate of climate change, and so far, we have not adequately addressed this inevitable issue.