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Implications of Snowball Earth Climate Change Event

Over the past billions of years, the earth has gone through unprecedented climate changes. This is evident with reports of climate change events. According to Hoffman et al. (2017) climate change events refer to both long term and extreme weather changes. This particular term is associated with the emergence of extreme and abrupt changes in climate. Such events have implications on the earth and its inhabitants, thus raising the need for extremely rapid responses. Such events are statistically rare. They occur when an unusual climatic occurrence alters the whole climatic ecosystem. Examples of such events include; the Snowball Earth, Eocene Thermal Maximum and the Younger-Dryas event (Tang & Li 2016). It is upon this understanding of climate change events that this paper discusses the Snowball Earth event and describes it in the context of radiation balance.

Description of Snowball Earth Event

The Snowball Earth hypothesis posit that at one point in time, the earth’s surface was entirely frozen. This event is reported to have transpired at least once. Its time of occurrence is reported to extend from 720 million years ago (Mya) to 630Mya (Tang & Li 2016). During this time, the Neoproterozoic earth surface froze for a prolonged period of time. This led to formation of a thick layer of ice that covered oceans and some parts of the earth surface, especially in the highlands as seen with the glacial mountains. Tang and Li (2016) note that Snowball Earth event is also known by the name Cryogenian. The last phase of the event occurred between 660 and 630 Mya and it was referred to as the Marinoan glaciation. This event is attributed to lowering of greenhouse gases in the atmosphere as a result of weathering of the tectonically mediated rocks. This coincided with the dimming of the sun thus could not provide adequate radiations to melt the glacier.

Impacts of Snowball Earth Event

The resultant impacts of the Snowball Earth event had extensive effects on the physical and biological environment. Tang and Li (2016) note that the event led to reduced greenhouse gases in the earth’s atmosphere. The principle gases that reduced include methane (CH4) and carbon dioxide (CO2). Coupled by the dramatic alterations in the three cycles are explained using the Milankovitch cycles, then the physical environment resulting from the Snowball Earth was colder. This made the earth cold and snow capped. Ice and snow is evidence of low solar radiations which barely reach the ground to melt the glaciers. The lack of a positive feedback from solar radiations means that the earth’s physical surface was unproductive. The lack of self-sustaining capability of the earth made it inhabitable. This event is explained using figure 1 below which shows the three gases and how they have to balance in the atmosphere to support life.

An imbalance between the three gases means that the earth would be covered by glacier and thus, unable to cater for human lives. The occurrence of volcanoes and hot vents, together with global warming are noted as making the earth balance its radiations thus inhabitable. This was noted during the Snowball Earth Event where the glacial cover on water bodies led to reduced oxygen concentration leading to extinction of algae (Tang & Li 2016). The extremely unfavorable and low temperature further caused death and extinction of pre-glacial plants and microorganisms. On the other hand, the resulting conditions coupled with a new chemistry of the ocean favored the Cambrian explosion and the development of Ediacaran fauna.

Figure 1: Gases that Shape Earth’s Climate and Support Life (Hoffman et al, 2017).

Factors that Contributed to or Caused Snowball Earth

The Snowball Earth event is believed to be in line with the Milankovitch cycle which explain the process of earth’s persistent glacial and inter-glacial periods. This model explains that the episodic formation and appearance of glacier as noted with the Snowball Earth event is because of cyclic changes in the circumnavigation of the earth around the Sun. The turning of the earth on its orbit around the sun causes variations in axial tilt, precession and eccentricity creating three main cycles that are collectively known as the Milakovitch Cycles. They are named after Milankovitch Milutin, a mathematician and astronomer from Siberia. When the three cycles are varied in unison, then it alters seasonality of the sun’s radiation reaching the surface of the earth. This creates periods of either decreased or increased solar radiations which has a direct impact on the climate system of the earth. This translates into formation or retreating of glaciers. While explaining this, Deitrick et al. (2018) are keen to specify that climate change and formation of glaciers does as a result of the three variables does not dependent on the solar energy that reaches the earth’s surface. However, the three cycles affect the location and seasonality of solar energy around the Earth’s surface. The eccentricity cycle is dependent on the shape of the earth’s orbit in relation to the position of the sun. Eccentricity fluctuates depending on the orbital shape as depicted in image 1 below. The fluctuations create either more or less ellipticity on a cycle estimated at 100,000 years (Zalasiewicz & Williams 2016). Such oscillations are important to the formation of glacier since it alters the distance between the earth’s surface and the sun. The change in the distance of short wave radiations reaching the

earth determines which areas the glaciers will form.

Image 1: Eccentricity Cycle (Deitrick et al, 2018)

The second cycle is instigated by the axial tilt. This refers to the change in inclination of the earth on its axis in regard to its plane of orbit revolving around the Sun. The oscillations change at a rate of 21.5degrees in 41,000 years as illustrated in image 2 below (Zalasiewicz & Williams 2016). The more the earth tilts, the lesser the glacier because of warmer winters and hotter summers.

Image 2: Axial Tilt (Deitrick et al, 2018)

The third cycle is known as earth’s precession. This refers to the slow wobbling of the earth as it spins around the orbit on its axis. The wobbling between the North Star (Polaris) to the South Star (Vega) influences the formation of glacial sheets. Precession has been increasing at a rate of 23,000 years as shown in image 3 below.

Image 3: Precession and formation of glacier (Deitrick et al, 2018)

The wobble is associated with significant alterations of climate. The combination of these three cycles therefore justifies the possibility that the axial tile, precession and eccentricity worked in unison in creating the Snowball Earth Event. It is argued that the unexpected convergence of extremes of these three cycles created extreme glaciers.

Conclusion

To this end, this paper acknowledges that the earth’s climatic condition has been changing over the past 4 billion years. This is evident with the Snowball Earth event which happened 720 million years ago (Mya) to 630Mya. The event led to reduced oxygen concentration thus extinction of aquatic life such as algae as well as pre-glacial plants and microorganisms. The new conditions also favored the Cambrian explosion and the development of Ediacaran fauna. The event is attributed to the three cycles as explained using the Milankovitch cycles.