The earth typically contains three main settings for climate:
Snowball – when the planet is frozen all over.
Greenhouse – when there are no sheets of ice and tropical temperatures reach the poles.
Icehouse – when the surface of the earth contains ice in varying extents.
Our planet has seen five ice ages and as of now, we are in the inter glaciation period of the fifth ice age. An ice age is a period which comprises of a long-term decrease in the earth’s temperature. A long-term ice age is marked by multiple pulses of cold and warm climates known as glacials and interglacials respectively. Glaciogically, an ice age involves extensive sheets of ices and glaciers in the Southern and Northern hemispheres.
This is How it Went Down in History…
The reasons behind the periodical advancement and retreat of ice are still shrouded in mystery that glaciologists are trying hard to unravel. This is how far they have come to understand the history of ice on earth:
The Huronian Ice Age – Snowball Earth
2.4 – 2.1 Billion years ago
- The Earth comprised of primitive life forms – unicellular organisms.
- This age occurred in the wake of the Great Oxygenation Event (GOE) – when an immense increase in the atmospheric oxygen decreased methane levels drastically.
- Varying causes have been studied; lowered methane and carbon dioxide levels (due to 250M years of volcanic inactivity), the orbiting of earth around the sun and/or the positioning of land masses.
The Cryogenian Ice Age – Big Freeze
850 – 630 Million years ago
- Records the coldest temperatures ever experienced by the planet
- Marks the emergence and evolution of complex life forms
- Probable causes – weakening of greenhouse effect due to plummeting levels of carbon dioxide, thus decreasing the temperatures eventually
- Two Cryogenian ice ages – Sturtian Glaciation (between 750 to 700 million years ago) and Marinoan Glaciation (between 660 to 635 million years ago). Glaciologists are still trying to figure out the exact happenings, but there is controversy regarding the fact that whether the planet became a snowball during these two deep freezes of glaciation or not.
The Andean-Saharan Ice Age – Mass Extinction
460 – 430 Million years ago
- The center of glaciation migrated from Sahara to South America
- It is considered as a minor ice age, coinciding with the first of the Big Five mass extinctions.
- The occurrence of this ice age brought about the chain of events that led to the Ordovician-Silurian mass extinction.
- The first mass extinction affected marine life drastically – eradicating about 85 percent of marine species.
The Karoo Ice Age – Plant Invasion
360 – 260 Million years ago
- Features two distinct ice peaks that may be considered glaciations; the Mississippian (between 359 to 318 million years ago) and Pennsylvanian (between 318 to 299 million years ago) periods.
- This ice age may have occurred as a result of land plants taking over the planet after the ecosystem recovered in the Cryogenian glaciation.
- The plants performed photosynthesis which increased the atmospheric oxygen. This decreased carbon dioxide, hence triggering the ice age.
- Some evidence suggests that the ice advanced and retreated from/to the poles in cycles
The Quaternary Glaciation –The Current Ice Age
2.58 Million years ago – Present
- It was triggered by the decreasing carbon dioxide levels due to the weathering Himalayas, as well as plate tectonics, astronomical cycles, atmospheric composition and ocean currents.
- Has already featured 40,000 to 100,000 year cycles of glacials and interglacials.
- The major effects of this glaciation period include the creation of millions of lakes, changes in the sea level, deposition of materials and erosion, abnormal winds and the modification of the river systems.
- The ice age will end once the Antarctic and Greenland ice sheets melt.