FSU assistant professor’s research helps determine origins of plate tectonics

A Florida State University faculty member’s research is helping to uncover more about the conditions necessary for the beginnings of life on Earth.

FSU Assistant Professor Richard Bono was part of a multi-institution team that found evidence that the planet’s magnetic field was stable from 3.9 to 3.4 billion years ago, a time when scientists think life may have first originated. Their research was published in Nature.

Bono explained more about what the team found and its implications for the origins of plate tectonics and life on Earth.

What did the research team find?
Our research showed that that Earth’s magnetic field was stable from 3.9 to 3.4 billion years ago, which corresponds with the oldest known fossils. Unlike earlier research, which took data from a single site, we measured magnetic carriers found in the mineral zircon from two separate ancient continental masses. The findings suggest that the magnetic field was stable and nearly identical for over half a billion years. This unvarying field could be explained by continents that were fixed in place, but for most of Earth’s history, the rocky plates that make up the continents were in constant motion on the surface of the planet — a phenomenon called plate tectonics. This finding helps us pinpoint when mobile plate tectonics may have started.

Why is this important?
Plate tectonics are thought to be one of the fundamental factors in existence of life on Earth. The present-day configuration of continents and oceans, as well as supercontinents like Pangea, is because of plate tectonics. Through the creation and destruction of rocky crust, plate tectonics are thought to control the cycling of elements necessary for life. However, the timing of when mobile plate tectonics started is unknown. If life on Earth originated about 3.8 billion years ago, it would have been during this stagnant regime. This finding suggests that modern mobile plate tectonics are not a requirement for the origin of life, expanding our understanding of what makes a planet habitable.

How did this study expand on our existing understanding of the Earth?
Previous research documented evidence for the presence of a magnetic field coming from the Earth’s core as early as 4.2 billion years ago. But that data just came from Australia. Because it was from a single continent, we couldn’t use it to detect plate motion. This study adds new data from a different continent, allowing us to investigate relative variations in field strength from the different locations, which could help infer possible plate motion.

How did you complete the research?
We analyzed rock samples collected during field expeditions to Australia and South Africa for individual zircon grains less than a millimeter in size. We measured the strength of the sample’s magnetization in a magnetically shielded laboratory at the University of Rochester by heating the sample grain with a laser and measuring how the magnetization changed with an ultra-high sensitivity magnetometer. We also measured the ages of each zircon grain at the Geological Survey of Canada using a superhigh-resolution ion microprobe.

With that new data, we could perform new statistical analyses and compare those with existing plate motion models. We found that what we saw in our new data set could not be explained by normal variation of the plate tectonic processes at work for at least the last 600 million years.

Who else was part of this research?
This study was a multi-institution endeavor led by University of Rochester Professor John Tarduno, with other co-authors from the Geological Survey of Canada, University of California Santa Cruz, University of Johannesburg, University of the Witwatersrand, University of Arizona, University of KwaZulu-Natal and Geological Survey of Japan. The research was supported by the National Science Foundation.