Did you know that scientists can reconstruct the Earth’s past climates thousands to millions of years ago?
As we celebrate Global Warming and Climate Change Consciousness Week (Nov 19-25), let us learn how fossils are used in determining ancient climates and how they teach us about climate change.
The study of past climate is known as Paleoclimatology. While we can’t go back to the past to see what the ancient climates were, luckily, nature has provided us with climate proxies. These proxies are imprints from our past that preserve our climatic history. Some proxies that we use in paleoclimate studies include shelled organisms and plant fossils.
One standard method for determining ancient climates is by analyzing the chemical composition of shells of fossilized marine animals like forams (shelled microorganisms). The oxygen isotopes in shells give an indication of the temperature changes in the ocean over the last millions of years. Their abundance may also indicate ancient environmental conditions, wherein they typically proliferate in warmer weather. Clamshells also have annual growth bands. The space between each band depends on the environmental conditions during the time when the growth bands were forming.
Meanwhile, we know that plants cannot root in an inhospitable environment. In each environment, they develop specific characteristics to help them adapt and survive. These make them a reliable indicator of their climate and ecology. Typically, plants in tropical regions have smoother and larger edges, while plants that live in cooler regions are more jagged and have smaller leaves. When these are fossilized, we can get an idea of what climate they lived in.
The Earth’s climate changes over the past millions of years are due to several factors operating together. The changes in the position of continents may close off or open up new routes of ocean currents, which can then change the distribution of temperature over the Earth’s surface. Sea-level changes in response to mountain building and continental drift may have also caused paleoclimate changes. Generally, the sea level is high in times of warmth. Other factors that contribute to climate change include variations in atmospheric chemistry and the Earth’s orbital position to the Sun.
The Earth’s climate has undergone extreme changes over its geologic history. And by studying past climates through fossils, we can better understand how climate will change in the future.
Text and image by the NMP Geology and Paleontology Division
© National Museum of the Philippines (2022)