The earth is changing all the time. The crust of Earth is called the lithosphere, and it is made out of 15 to 20 bigger tectonic plates and dozens of smaller ones. The plates are like cracked shells, and they are moving on hot, molten rock (Earth). Sometimes the crustal plates hit each other, but they can also move further from each other. This moment is called plate motion or tectonic shift, and it can cause eruptions. Our planet looked really different in the past. Around 250 million years ago, there was only one big continent called Pangaea. The ocean that surrounded it was called Panthalassa. Over a very long time, the movement of crustal plates can cause climate change. For example, Great Britain used to be close to the equator, but it was a long time ago—to be exact, over 300 million years ago during the Carboniferous Period. Since the climate is warmer closer to the equator, it was also warmer in Britain compared to the climate they have now. The movement of the plates also causes volcanic activity, which contributes to climate change. The movement of the crustal plates continues nowadays.
As earlier said, the Earth’s crust is moving all the time. To be exact, the average speed of the crustal plate is 1.5 cm per year. This is the perfect speed to maintain the earth’s temperature. For hundreds of millions of years, Earth’s temperature has warmed and cooled naturally. Humans have pushed the CO2 levels to the highest that they have been in the last 2 million years.
The warmer and colder times in Earth’s geological history are called ‘Hothouse’ and ‘Icehouse’ climates. In the Cretaceous ‘hothouse’ (around 145 million to 66 million years ago), the atmospheric CO2 levels were over 1,000 parts per million, with current levels at 420, and therefore temperatures were almost 10 °C higher than today. Earth’s temperatures started to cool down around 50 million years ago, and this period is called the Cenozoic Era. In this era, the temperatures were almost 7 °C cooler than today. Scientists think that the cause of these changes was the Earth’s tectonic plates.
During the movements of crustal plates, carbon dioxide is released into the atmosphere. For example, it happens at mid-ocean ridges, where two plates are moving away from each other. It also happens when the ocean plate goes under Earth’s plate and, on the way down, releases CO2 because of the volcanic activity. Earth’s tectonic carbon conveyor belt moves large quantities of carbon deeper into the Earth’s surface, from the crests of the mid-ocean to the subduction zones, where ocean plates holding deep-sea sediments are redirected back into the Earth’s interior. Such processes are important for the Earth’s climate and habitability. Scientists have made models of the ways in which the crustal plates are moving. By using these models, they understood that during the Cretaceous ‘hothouse’ climate was very hot because the crustal plates were moving a lot faster than they do nowadays. The faster movement released a lot more CO2 emissions into the atmosphere. During the Cenozoic ‘icehouse’ climate, it started to cool down because the movement of crustal plates slowed down.
When tectonic plates collide, they form mountains. For example, the Himalayas and the Alps were formed this way over 50 million years ago. Scientists used to think that these movements should lead to a reduction in CO2, because the crustal plates that move closer to each other slower the speed. So, based on the old models, the climate should have become warmer, not cooler. The cooling of the climate is caused by carbon-rich deep-sea sediments. These sediments were pushed downward during the movement of the crustal plates, and when the volcanoes erupted, CO2 was released. In addition, the scientists found that erosion also contributed to the cooling of the climate. Rainwater erodes rocks. The minerals in the rocks then flowed with the water into rivers and oceans. Marine organisms then use these minerals to build their shells. This process was continuous, with new mountains forming and eroding at the same time, and eventually the climate became colder 50 million years ago.
Also, the way the continents are positioned on Earth affects the climate. Different surfaces reflect the sun differently. Land surfaces reflect more than open water. Also, surfaces that are covered with snow or ice reflect more sunlight. The sun’s reflection from Earth is called albedo.
Around 720 million years ago, we had another huge continent called Rodinia. Most of the land area of Rodinia was close to the equator (50%), 40% of the land was in temperate areas, and only 10% was in polar areas. Because so much of the land was in an equatorial zone, it made the Earth’s temperature cold. Also, the albedo on Earth was a lot higher than it is nowadays because during that time there was also no vegetation. Because of all of this reflection, there was the first big ice age on Earth, and it was called the Cryogenian Period Snowball Earth. This period lasted around 60 million years.
Sources:
https://www.bgs.ac.uk/discovering-geology/climate-change/what-causes-the-earths-climate-to-change/
https://oceanservice.noaa.gov/facts/tectonics.html
https://www.sydney.edu.au/news-opinion/news/2022/05/26/how-plate-tectonics-have-maintained-earth-s–goldilocks–climate.html
https://environmental-geology-dev.pressbooks.tru.ca/chapter/plate-tectonics-and-climate-change/
