A 200 million year old early Jurassic aged fossil leaf. The leaf belongs to a plant species called Sphenobaiera spectabilis which is an ancient ancestor of the modern plant species Ginkgo biloba.
A UCD research team has authored a new scientific report on the mass extinction event at the start of the Jurassic Period. There have been five major extinction events during the history of life on earth; the best known wiped out the dinosaurs 65 million years ago. But in earlier times, the Triassic-Jurassic (Tr/J) extinction of 200 million years ago, destroyed more than 80 per cent of the plant species living in certain areas.
Despite the record of destruction, many scientists have doubted whether the Tr/J extinction was a “real” extinction event. They say that the decline in species was a product of natural cycles, or bad data, much like today’s arguments about climate change.
Through examining exceptionally preserved fossil plants in Greenland, the UCD-led team has shed new light on the Tr/J extinction and the time immediately prior to the event. Their findings, published in the journal Paleobiology, show that plant communities before the extinction event were already suffering losses of biodiversity. With rising atmospheric carbon dioxide in the late Triassic, the plant communities were deteriorating and species were becoming extinct. And the decline in biodiversity was self-reinforcing; losing biodiversity before the Tr/J extinction event made these ecosystems susceptible to even small changes in CO2. Finally, because the ecosystems were already suffering, small shifts in climate change caused terrible destruction to species.
A campsite in Greenland where Triassic and Jurassic fossil plants were collected as part of a National Geographic expedition in 2002. The scree covered rocks behind the tents are approx 200 million years old.
Ongoing research in McElwain’s group in UCD will investigate how plants today respond to different levels of atmospheric carbon dioxide, oxygen and sulphur dioxide pollution. McElwain and her colleagues hope to use these ancient extinction events to shed light on the effects of modern-day climate change.
