The End-Triassic Mass Extinction

The primary focus of my research at Brown University was the end-Triassic Mass Extinction. This ecologic and climatologic disaster, which occurred ~200 million years ago, was one of the most destructive in the history of life. It led, many would argue, to the development of the modern ecosystem and paved the way for the dominance of dinosaurs. My goal was to see what changes where happening in the ocean at that time.

Hopanes, a class of compounds created by bacteria.

To do this, I extracted fossil molecules from rocks deposited on the bottom of ancient Triassic and Jurassic oceans. Fossil molecules, also known as biomarkers, are chemicals created by once-living organisms that can survive many millions of years and be traced back to the organism that created it. (If you are interested, please read this great explanation of biomarkers on Rogers Summons’ website.)

Steranes, A class of compound created by eukaryotes

Both the preservation of these chemicals, and the specific molecules themselves, can tell you a lot about the environment at a given time. Because different organisms live in different environments, and because only some environments preserve these molecules, I can reconstruct things like the amount of oxygen in ancient marine waters, how much nitrogen was in the water, and which species of algae are most dominant.

While these may seem like trivial questions, their answers can provide great insight into what the ultimate cause of destructive events like the end-Triassic mass extinction. A lack of oxygen or lack of nitrogen in large portions of the ocean can disrupt the organisms that are at the base of the food chain. Because these organisms are so crucial to any ecosystem, major shifts in species can have dramatic effects all the way up the food chain.

Laboratory set up for separating different classes of compounds.

One specific phenomenon at the base of the food chain that has driven much of my research is referred to as ‘photic zone euxinia.’ Many organisms deep in the ocean, where there is little or no oxygen, essentially ‘breathe’ using various forms of the element sulfur. The byproduct of this activity is hydrogen sulfide, which is extremely toxic to most forms of life.

If there is an extreme lack of oxygen in a given body of water, hydrogen sulfide can expand away from the deep waters and move up to the surface. Photic zone euxinia occurs when this hydrogen sulfide reaches the portion of the water column that receives light from the sun. This is an extreme condition (it occurs in some areas on Earth today: the Black Sea and the west coast of Africa, for example), and only a very specific class of organisms can survive in it.

Photic zone euxinia (Green waters) off the coast of Namibia. Credit: NASA

Green and purple sulfur bacteria are the organisms that thrive in photic zone euxinia environments. Everything else, essentially, perishes. Luckily for people trying to find out if this phenomenon happened in the past, these organisms create a unique molecule, isorenieratane, that cannot be traced to any other organisms. One of my major goals is to see if this phenomenon occurred during the end-Triassic mass extinction, by looking for isorenieratane in rocks deposited during the extinction.

This project is the result of a fruitful collaboration with Julio Sepulveda at MIT, and most of the hunt for these chemicals occurred in the laboratory of Roger Summons there – I am extremely grateful to both of them for this opportunity. Stay tuned for the publication of the exciting results of this study!

Abstracts and Publications:

KASPRAK, AH, Sepúlveda, J, Price-Waldman, R, Williford, KH, Whiteside, JH, Summons, RE. 2011. Anoxia Precedes the end-Triassic Mass Extinction: Evidence from the Kennecott Point Formation, British Columbia. AGU Fall Meeting, December 5th-9th, 2011. Abstract #B11B-0483


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