Trinity scientists explore how Earth’s orbit affects the carbon cycle

Mudstone sediments in Wales have helped to unearth prehistoric climate patterns

Two Trinity researchers, Assistant Professor of sedimentology Micha Ruhl and Dr. Weimu Xu, have recently co-authored a study on the effect of the Earth’s orbital shape on the carbon cycle and global warming around 200 million years ago. In more recent times, it is clear that human activity has caused a detrimental effect on carbon levels in our atmosphere. If carbon emissions continue in their current levels, we will rapidly approach a mass extinction event, the sixth in Earth’s history. The work by Ruhl and Xu and their team examines two of five major mass extinctions we have undergone in the Earth’s history. Analysing past climate changes and carbon levels during mass extinctions will aid in combating very current climate threats. 

The research focused on two mass extinctions in particular: the Triassic-Jurassic Mass extinction and the Toarcian Oceanic Anoxic Event. The Triassic-Jurassic Mass extinction wiped out around 76% of marine and terrestrial species on Earth at the time. This took place around 201 million years ago when the supercontinent Pangaea began to drift apart. Plate movement brought about large scale volcanic activity, increased carbon dioxide levels, and global warming. The Toarcian Oceanic Anoxic Event was a time of significantly low oxygen levels in the world’s oceans that occurred around 183 million years ago. Similarly to the Triassic-Jurassic Mass extinction, it was another historical period of warming and high atmospheric carbon dioxide levels.

“The research details how these orbital changes affected global climates during the mass extinctions”

Ruhl and Xu, as a part of an international research team from Stellenbosch University, the University of Exeter, the University of Oxford and the University of Nottingham, examined the chemical composition of mudstone deposits in Llanbedr borehole, in Cardigan Bay Basin, Wales to learn more about these two mass extinction periods. They discovered that periodic changes in the Earth’s orbit around the sun may have been at least partly responsible for warming and carbon dioxide levels in these periods. The Earth’s orbit is currently elliptically shaped, like an oval, with the sun slightly off centre. This means there are times in its orbit when the Earth is relatively close to the sun, and times when it is further away. This orbital shape is not fixed, but rather changes from elliptical to almost circular in a periodic cycle that takes around 100,000 years. Due to this, the Earth receives different amounts of energy due to its changing proximity to the sun. The research details how these orbital changes affected global climates during the mass extinctions and has been published in Proceedings of the National Academy of Sciences (PNAS), a leading journal. 

“Our work shows that for the 18 million years or so in between the Triassic–Jurassic mass extinction and the Toarcian Oceanic Anoxic Event, Earth’s global carbon cycle was in a constant state of change,” said Ruhl. He notes that although the phenomenon was known to affect glacial cycles, the effect on the carbon cycle is a relatively novel discovery. Ruhl was joined in the research group by fellow Trinity researcher and Marie Skłodowska-Curie Fellow, Dr. Weimu Xu. The work carried out by Ruhl, Xu and the other team members gives us vital insights into the natural carbon cycle outside of human impacts. Previous global climate events, and certainly mass extinctions, could give us an idea on how best to approach current crises in our climate. Though history would predict that the next big shift in our climate would be a period of cooling, we are really in uncharted territory when it comes to man-made damage to our ecosystem. Perhaps the best guide to what could be a bleak future climate is to look back into the past. 

The research was funded by Shell International Exploration & Production B.V., the Natural Environment Research Council, and the International Continental Scientific Drilling Program.

Lucy Fitzsimmons

Lucy Fitzsimmons is the current Deputy SciTech Editor of Trinity News, and a Senior Fresh Chemical Sciences student.