Skip to 0 minutes and 7 secondsWe've looked at the extreme conditions that snowball Earth ice ages brought, and about their role in the emergence of life on the Earth. But given the wide scale occurrence and extreme nature of snowball Earth climates, it seems obvious to ask, how did Earth escape being trapped in such an extreme, icy condition forever? Well, it is thought that the end of snowball Earth ice ages is due to the increase in the content of the greenhouse gas CO2 in the atmosphere. It is important for us to understand that a smaller amount of CO2 in the atmosphere is characteristic of ice age climates, and a larger amount of CO2 is characteristic of warmer climates.

Skip to 0 minutes and 57 secondsThis is because CO2 is a key ingredient in keeping our planet warm. During a snowball Earth climate state, the consumption of CO2 was greatly reduced. This was due to the thick ice sheets that sealed the earth's surface, effectively stopping CO2 from being consumed by bacteria during photosynthesis, and by rocks through weathering. But despite the earth being covered in thick ice sheets, volcanoes continued to release CO2 into the atmosphere, tens to hundreds of millions of years.

Skip to 1 minute and 33 secondsThis combination of the continued release of CO2 and the reduction of consumption of CO2 through bacteria and rocks led to a slow buildup of CO2, meaning that over time, enough heat was trapped by CO2 to melt the vast ice sheets that covered the Earth's surface. Understanding how CO2 regulates Earth's temperature helps us to not only explain past extreme climate events like snowball Earth, but also to understand our planet now, and its changing climate. Earth's volcanoes are key contributors to CO2, ejecting an estimated 200 million tonnes each year. But just as there are natural processes of producing CO2, there are natural processes for consuming and absorbing CO2.

Skip to 2 minutes and 29 secondsJust like a thermostat, the amount of CO2 in Earth's atmosphere regulates climate and atmospheric temperature. Rising atmospheric CO2 content produces warming. Declining atmospheric CO2 levels produce cooling. A key CO2 consumption process are caused when rocks are weathered away, with most rock weathering occurring at the equator, as weathering intensifies when temperatures rise. This CO2 consumption occurs through chemical reactions with the mineral calcium silicate that is abundant in volcanic rocks. These reactions form the mineral calcium carbonate. This is also what forms scales in water boiling kettles. The solid calcium carbonate is buried at the bottom of the world's ocean, removing it permanently from the atmosphere for millions of years.

Skip to 3 minutes and 28 secondsThe buried calcium carbonate is eventually cycled back to the atmosphere when the rocks are melted deep inside the Earth to release C02. This balance between CO2 consumption and production controls the surface temperature of our Earth. This is crucial for regulating a climate that can support life.

Escaping from Snowball Earth

In this video, Dr Ernest Chi Fru explains how Earth managed to escape from Snowball Earth ice ages.

The end of Snowball Earth ice ages is thought to have been triggered by an increase in the levels of the greenhouse gas, CO2 in the atmosphere. High levels create the so-called greenhouse climate we experience today, and low levels are typical of ice ages.

CO2 as Earth’s thermostat

The level or amount of CO2 in the atmosphere is thought to regulate Earth’s climate. Sunlight penetrates the atmosphere and heats up Earth’s surface.

But it is CO2 in the atmosphere that effective regulates the amount of heat from sunlight that is reflected back to space. CO2 absorbs and conserves that heat, just like a sponge absorbs water.

Consumption of CO2 via weathering

Volcanoes can increase the levels of CO2 in the atmosphere, but it is the the wearing away of calcium silicate (CaSiO4) rich rocks by CO2 that removes it from the atmosphere. This process is called weathering.

It is thought that Snowball Earth’s happened suddenly and were caused by rapid weathering that effectively sucked CO2 out of the atmosphere.

The greater the number of fresh rocks that can be weathered by reacting with CO2, the lower the amount of CO2 in the atmosphere and the greater the amount of calcium carbonate (CaCO3) buried at the bottom of the sea.

Weathering increases with temperatures, this is why soils along the equator are the most weathered on Earth compared to soil in the temperate regions.

The reaction between CaSiO4 and CO2 works like a thermostat that regulates Earth’s temperature and climate.

Summary

Looking at how our planet escaped Snowball Earth helps us to understand our climate now and the crucial role CO2 in the atmosphere plays.

The balance between the production of CO2 and its consumption via weathering is crucial for regulating a climate that can support life.

Just as we need oxygen in the atmosphere to have a planet that is habitable, we also need CO2 as without it the planet would be inhospitably cold.


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Extreme Geological Events

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