This blog is written by Emily Dearing Crampton-Flood, a postdoctoral researcher at the University of Manchester. After studying Chemistry at the University of Bristol, Emily decided to move into Geoscience, and the field of paleoclimate reconstruction. Her favourite new lockdown hobby is yoga. You can follow updates of her current project at Manchester on Twitter @creltemp.
Fossil bacteria tell us about climate millions of years ago
I am an organic geochemist interested in molecules preserved in ancient sediments, and the stories they can tell about past climates. When I was younger, I went through a dinosaur phase (don’t we all) and used to daydream of digging up a T. Rex in a remote corner of the world. In a way what I do now is similar, because I am looking at molecules, or ‘biomarkers’, left behind by bacteria that died millions of years ago. As temperature changes, bacteria change the molecules they produce; so these biomarkers can tell us how warm temperatures were millions of years ago.
At the moment, I am reconstructing ancient land temperatures to solve two different problems:
The effects of greenhouse gas emissions on climate
The Earth’s climate is warming. Many ecosystems – from coral reefs at the equator, to tundra in the Arctic – are under threat due to changing conditions in the oceans and atmosphere. The increasing concentration of greenhouse gases in the atmosphere is causing, and will continue to cause, global warming. Climate models estimate that global temperatures will increase more than 2 °C over the next 80 years (Fifth assessment report of the Intergovernmental Panel on Climate Change, 2013).
But how do we get to these estimates, and why are they so important? The answer lies partly in computer modelling – a process where scientists use maths and equations to describe how heat moves around the planet. Another way is to look to the Earth’s past. Studying periods of the Earth’s history when it was much warmer than today can help us predict what might happen in our future. Luckily, we have several examples of warm periods in the geological past to learn from, such as the Cretaceous, a period of geological time that stretched from 145 million to 66 million years ago.
The Earth was a very different place during the Cretaceous. Fossil palm trees, crocodiles, and pollen grains show geologists that Antarctica and the Arctic were very warm and humid 90 million years ago! We also know that the concentration of carbon dioxide in the atmosphere during the Cretaceous was similar to what we predict for the end of this century. These features make the Cretaceous a good candidate for us to learn about what the future might hold for the world’s climate.
I am currently reconstructing land temperatures at a variety of sites across North America at the end of the Cretaceous. From this, we will be able to look at how warm it really got – from New Mexico to the Arctic – when greenhouse gas levels were as high as is predicted by the end of this century.
The effects of a meteor impact on climate!
66 million years ago, at the end of the Cretaceous, a large asteroid impacted planet Earth and likely caused the most recent major mass extinction of animals and plants. Infamously, this event was responsible for the demise of the dinosaurs. Our understanding of what happened to temperatures on land after the asteroid impact is quite vague. Some scientists suggest that the dust thrown into the atmosphere by the impact blocked sunlight and led to freezing temperatures which destroyed many ecosystems. Others suggest that the impact caused the sudden release of greenhouse gases that led to runaway global warming. Others still suggest that the extinction was nothing to do with the impact of the meteor, but was caused by the outpouring of greenhouse gases over millions of years by volcanic eruptions.
Over the next few years I will be reconstructing temperature changes that happened during and after this famous extinction event. Did it get suddenly colder, did it get suddenly warmer, or did it gradually warm over millions of years? This is important, because we can stop “guessing” what kind of climate change led to this extinction. We can also learn how long it took for the climate on Earth to recover from this drastic event. It might also reveal why certain forms of life survived (including our ancestors, early mammals).
Out in the field
To answer these two problems, I need to collect samples of Cretaceous and Palaeogene rock that contain lots of fossilised bacteria. The best rocks to do this are coals, which are fossilised peats from swampy environments. In summer 2019 I went into the field with Rhodri Jerrett (University of Manchester) and Greg Price (Plymouth University). We went to six locations in Canada, stretching all the way from southern Saskatchewan (near the border with the USA) to a site less than 150 km away from the Arctic circle in the Northwest Territories. It was my first fieldwork experience and was very different to working in the geochemistry lab I was used to up until that point!
In the field we encountered small chicken-like dinosaur bones and plenty of slippery kaolinite, which made clambering around the rocks somewhat precarious. We collected lots of coal samples with fossils of bacteria that lived in the Cretaceous and Paleogene.
Currently I am working on the next step, which is to get into the lab and start work on unravelling the story within each sample. Each horizontal layer of coal has the power to paint us a detailed picture of the climate millions of years ago, and could therefore help us to predict what sort of changes we can expect in the upcoming few centuries…
Acknowledgements: This project is made possible by a NERC Standard Grant (NE/S002324/1), and is supported by the Universities of Manchester and Plymouth. Other project members not named in the text are Bart van Dongen (Manchester) and Sabine Lengger (Plymouth). We thank the following for granting us land access, and for their logistical support: the Aurora Research Institute, the Sahtu Renewable Resources Board, the Tulita Renewable Resource Council, the Sahtu Land and Water Board, Tulita District Land Corporation, Parks Canada, the staff at Grasslands National Park, the Geological Survey of Canada (Calgary), James McPherson, Ritchie Hordenchuck, Corbin Selody, Marion Knudsen, Calin Griffiths and Richard Fontaine.