A new study in the April 22 edition of the journal ‘Science’, reveals that volcanic activity associated with the plate-tectonic movement of continents may be responsible for climatic shifts from hot to cold throughout much of Earth’s history. The study, led by researchers at The University of Texas at Austin Jackson School of Geosciences, addresses why Earth has fluctuated from periods when the planet was covered in ice to times when polar regions were ice-free.
Lead researcher Ryan McKenzie said the team found that periods when volcanoes along continental arcs were more active coincided with warmer trends over the past 720 million years. Conversely, periods when continental arc volcanoes were less active coincided with colder, or cooling trends.
For this study, researchers looked at the uranium-lead crystallization ages of the mineral zircon, which is largely created during continental volcanic arc activity. They looked at data for roughly 120,000 zircon grains from thousands of samples across the globe.
Zircon is often associated with mantle plumes. If the zircon Hf model age is very close to its formation age (zircon U–Pb) – the magma could be subsequent of a depleted mantle plume. On the other hand, if the zircon Hf model age is older than its formation age, it can be concluded that the magma was derived from enriched mantle sources or was contaminated by crustal materials.
“We’re looking at changes in zircon production on various continents throughout Earth’s history and seeing how the changes correspond with the various cooling and warming trends,” McKenzie said. “Ultimately, we find that during intervals of high zircon production we have warming trends, and as zircon production diminishes, we see a shift into our cooling trends.”
Increase Charged Particles → Decreased Magnetic Field → Increase Outer Core Convection → Increase of Mantle Plumes → Increase in Earthquake and Volcanoes → Cools Mantle and Outer Core → Return of Outer Core Convection (Mitch Battros – July 2012)
One question unanswered in recent climate change debates, is what caused the fluctuations in CO2 observed in the geologic record. Other theories have suggested that geological forces such as mountain building have, at different times in the planet’s history, introduced large amounts of new material to the Earth’s surface, and weathering of that material has drawn CO2 out of the atmosphere.
Using nearly 200 published studies and their own fieldwork and data, researchers created a global database to reconstruct the volcanic history of continental margins over the past 720 million years.
“We studied sedimentary basins next to former volcanic arcs, which were eroded away over hundreds of millions of years,” said co-author Brian Horton, a professor in the Jackson School’s Department of Geological Sciences. “The distinguishing part of our study is that we looked at a very long geologic record – 720 million years – through multiple warming and cooling trends.”
The cooling periods tended to correlate with the assembly of Earth’s supercontinents, which was a time of diminished continental volcanism, Horton said. The warming periods correlated with continental breakup, a time of enhanced continental volcanism.