Climate Change

Natural Climate Change over Earth’s History
M. Cavanagh

Over the last 4.6 billion years, Earth has gone through a great number of geological and atmospheric changes that impacted the organic life that inhabited it. Earth’s geological record gives clues to the environment of Earth’s surface throughout the years, and provides insight on the type of wildlife that could be found at any given time. The atmospheric changes that our planet has gone through can also be studied through the geological record. The first atmosphere that developed was inhabitable for modern day plants and animals.  It was made up of methane, carbon dioxide, and other gases, but did not contain any free oxygen. This can be supported by the discovery of stromatolites in 3.5 billion year old limestone. These carbonate sediments indicate that carbon dioxide was present, and that there was a lot of it. All of these gases in the atmosphere would have resulted in a greenhouse earth, with a hot climate due to heat being trapped by the atmosphere. About 2.5 billion years ago oxygen became sufficient enough in the atmosphere to form red beds, which are beds of sandstone that has been turned red due to oxidation. The earliest signs of free oxygen can be found in iron deposits from 4.6 billion years ago to 541 million years ago. These iron deposits would absorb the oxygen released by anaerobes present at the time. A decrease in the number of iron deposits resulted in an increase of oxygen in the atmosphere, ultimately killing off any organisms that cannot survive with oxygen, and making way for other organisms to thrive. This transition can be marked by fossils of eukaryotes, which require an oxygen content of 0.02 PAL (present atmospheric level), from around 1.4 billion years ago. All of these changes in Earth’s atmosphere and climate can be evidenced by changes in the geologic record and can be used to study our present and future climate.

Earth’s geological record also includes sea bed sedimentation, which can be studied for clues on that period’s marine life, global climate, arrangements of continents, and so forth. The ocean currents are largely responsible for the transfer of heat throughout the globe, and therefore can have an effect on the global climate. Ocean currents can be changed over long periods of time by tectonic activity in the Earth’s crust. Around 250 million years ago, the supercontinent Pangea was beginning to break up, and form the continents we see today. This occurred over millions of years, creating continents, mountains, and new oceans as it happened. Eventually what is now Antarctica drifted to the south pole, where it formed a circumpolar ocean all the way around it. This ocean formed a clockwise current around the continent that blocked heat from reaching the landmass. This ocean current caused a large sheet of ice to form over Antarctica. As the ice sheet grew and spread, more and more sunlight was reflected away from Earth, this could be what caused a period of cooling of Earth’s global climate, which includes the present. Today’s global temperatures are around 10°C lower than they were during the Mesozoic Era. Changes in Earth’s climate occur over millions of years, and can be affected by many different things, including ocean currents and continental drift.

Earth’s history is full of drastic changes, some of which are mass extinctions of primary species at the time. There are five major extinction events known as the “big five”.  The second of these events occurred over 2-4 million years during the Devonian period. This extinction event has been debated as it takes place over a much longer time period than the other four. It has been separated into different events by many different people, and it is still unknown exactly what caused it, as it is difficult to discern a specific reason for such an extended period. The Kellwasser event was responsible for the extinction of the great coral reefs, jawless fish, and trilobites. The Hangeberg event was responsible for killing off the placoderms, and most of the early ammonites. Overall marine life took the brunt of the mass extinction and  great coral reefs would not reappear until 145 million years after. An estimated 75% of all marine fish families were killed during this period. One proposed theory for this extinction event is cooling of the planet due to an increased amount of trees and plant life that absorbed CO2 from the atmosphere. This would have switched the Earth from a greenhouse climate to an icehouse climate. Although marine life was heavily impacted by this change, terrestrial life was almost unaffected by it. The mass extinction at the end of the Devonian period marks the beginning of the Carboniferous period. As with all extinctions, the Devonian extinction event made way for other species to become the dominant life form, and for new species to form and evolve. Changes in the Earth’s atmosphere and climate can change more than just the geological record, it can cause mass extinctions like that of the Devonian period.

In the past 100-200 years humans have been increasingly growing and consuming earth’s materials. Some of these materials are coal and fossil fuels such as petroleum. The use of these fuels results in an enormous amount of carbon dioxide and other harmful gases to be released into the atmosphere. Earth has gone through and will continue to go through natural fluctuations in global temperature, from greenhouse to icehouse and back to greenhouse. However, humans have heavily disrupted this natural cycle by polluting the atmosphere, ocean, soil, and air. We have caused a greenhouse effect to occur in a very short period of time, causing ice caps to melt rapidly, and species to go extinct abruptly. The past four years were the hottest on record, winter temperatures in the Arctic have risen by 3 °C since 1990. By continuing to overuse fossil fuels we risk the destruction of ice caps, coastal cities, species, entire ecosystems, and even ourselves. In recent years there has been a huge push from environmental groups, schools, and now the UN for industries to change their policies to be more eco friendly. It is possible for us to stop further damage by reducing our carbon footprint in the way we live our everyday life. A lot of the burden to change is falling on individuals rather than companies that pump metric tons of carbon into the atmosphere and create enormous amounts of waste. Individuals can influence large companies to change by being mindful of the products they are purchasing, choosing local produce, cruelty free products, and sustainably made products.

Earth has an incredibly long and violent history, with extreme changes in climate, species, atmosphere, landmass locations, and ocean currents. The tectonic plates play a large role in the changes that occur on the surface, but other factors such as the sun, earth’s orbit, plant life at the time, as well as other factors  can drastically change the environment.




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