The Science of Soil

Fig.1. Banded sedimentary rock layers in Wyoming were drilled and sampled to obtain details of global warming (Credit: Scott Wing, Smithsonian Institution)

About 55.5 million years ago, the Earth experienced a period of sudden warming triggered by two rapid, immense releases of carbon dioxide into the atmosphere. This event, known as the Paleocene-Eocene thermal maximum (PETM), was originally thought to have occurred at either too slow or too fast a rate to be useful for addressing our own climate problems. The PETM was marked by temperature increases of 5℃ to 8℃ (9℉ to 15℉), along with a rise of sea levels, ocean acidification (seen in previous post), and extinction of deep sea organisms. Although most species survived and even flourished, it took 200,000 years for the world to recover from such high temperatures and carbon dioxide levels. New research suggests, however, that the PETM carbon emission rate may be close enough to hold lessons on modern global warming.

The chemical record

Research led by Gabe Bowens at the University of Utah aimed to create an accurate rendition of events that led to global warming 55.5 million years ago. Scientists drilled an 820-foot core out of the ground in northern Wyoming, which had ancient soils from before the PETM. The soil layers eventually turned to stone over the millennia and now show a record of changes in the Earth’s atmosphere. The sediment core was dotted with carbonate nodules, each of which contained different ratios of carbon isotopes, or varieties of the element carbon. By measuring the ratios of carbon isotopes, researchers can understand how and when carbon was added to the atmosphere.

The results tell of two rapid and sizable carbon release events during the onset of the PETM. Although the cause of the releases are unclear, more evidence points to the PETM as a viable model for modern global warming. The next steps for Bowens involve understanding the emission origins and the relationship between each release.

Fig.2. Sediment cores drilled from Wyoming’s Bighorn Basin are in a repository at the University of Bremen. The gray carbonate nodules hold the key to understanding global warming 56 million years ago (Credit: Bianca Maibauer, University of Utah)

Climate change in collecting

Sediment cores, like those taken from northern Wyoming’s Bighorn Basin, are very useful for studying climate of the ancient world. Although this core was drilled from rock, other sediment cores are drilled from softer substrates such as lake beds and wetlands. But they all follow the same mechanism: newer material is on top and significant changes are recorded in bands of different soil.

Although the rate of carbon release during the PETM was much lower than today, the analysis of cores yields some clues for our future. Ocean acidification and global warming are already occurring. We have experienced significant species loss, which is only expected to continue. Just as sediment cores map out Earth’s environmental history, animal specimens in museums show a drop in biodiversity over time. If we can better understand an ancient warming event, we can predict how the Earth might recover from modern climate change.



References:

Bowen, G.J., Maibauer, B.J., Kraus, M.J., Röhl, U., Westerhold, T., Steimke, A., Gingerich, P.D., Wing, S.L., & Clyde, W.C. (2014). Two massive, rapid releases of carbon during the onset of the Palaeocene-Eocene thermal maximum. Nature Geoscience. doi:10.1038/ngeo2316.

Riebeek, H. (2005, June 28). Paleoclimatology: A Record from the Deep. NASA Earth Observatory online. Retrieved from http://earthobservatory.nasa.gov/Features/Paleoclimatology/paleoclimatology_intro.php.

University of Utah. (2014, Dec 15) Past Global Warming Similar to Today’s [Press release]. Retrieved from http://unews.utah.edu/news_releases/past-global-warming-similar-to-todays/.

Glossary

Paleocene-Eocene thermal maximum (PETM)
A climate event around 55.5-55.8 million years ago in which there was global warming and massive carbon input into the atmosphere and ocean, marked by an initial temperature increase of 5°C.
carbon emissions
Release of carbon dioxide or other greenhouse gases into the atmosphere.
isotopes
Variants of a chemical element which differ in neutron number and have the same number of protons in each atom.