500 million years long history of CO2 revealed by fossil algae

The new reconstruction shows how CO₂-concentrations rose and fell in the earth’s atmosphere during nearly half a billion years in the geological past of the planet. Climate researcher Caitlyn Witkowski, first author of the paper and PhD student at NIOZ, says: “In our data, we see very high levels of carbon dioxide, reaching 1000 ppm as opposed to today’s 410 ppm. In this respect, present day CO₂-levels are not unique – but we have never seen the speed of these changes before. Changes that typically take millions of years are now happening in a century. This additional CO₂-data may help us understand the future of our planet.”

Phytane

For their reconstruction, Witkowski and colleagues selected hundreds of samples of marine sediments from all over the globe. A breakthrough in their research was the usage of only one indicator to infer a continuous record of CO₂-levels in deep time: phytane, a degradation product of the green pigment chlorophyll. Earth scientists often use different kinds of indicators (proxies) from plants and chemicals stored in ancient ocean sediments to reconstruct past environmental conditions.

Because chlorophyll is found all around the world, phytane is also found everywhere. Witkowski: “Phytane doesn’t change chemically over the course of time, even if it is millions of years old. With phytane, we now have the longest CO₂-record with one single marine proxy. This new data is invaluable to modelers who can now more accurately make predictions of the future.”