Plate tectonics is a fundamental factor in the sustained habitability of Earth, but its time of onset is unknown, with ages ranging from the Hadean to Proterozoic eon. University of Rochester’s Dr. John Tarduno and colleagues examined plate tectonics from a time 3.9 billion years ago, when they believe the first traces of life appeared on Earth. But they found that mobile plate tectonics was not occurring during this time. Instead, they discovered, Earth was releasing heat through what is known as a stagnant lid regime.
Plate tectonics allows heat from Earth’s interior to escape to the surface, forming continents and other geological features necessary for life to emerge.
Accordingly, there has been the assumption that plate tectonics is necessary for life. But the new research casts doubt on that assumption.
“Ideally, the presence or absence of a mobile lithosphere can be tested using paleomagnetism, but even the best preserved oldest rocks on Earth have experienced metamorphism, and this places severe restrictions on the type of magnetic carriers that might retain primary signals,” Dr. Tarduno and co-authors explained.
“Single-crystal paleointensity, whereby single mineral crystals that contain magnetic inclusions capable of recording the ancient field are studied, provides an approach to see through this metamorphism.”
“The only known detrital crystals that can be accurately dated, and that are able to provide constraints on lithospheric mobility spanning the multi-hundred-million-year timescales that typify plate-tectonic cycles, are detrital zircons bearing primary magnetic inclusions.”
Zircons are tiny crystals containing magnetic particles that can lock in the magnetization of Earth at the time the zircons were formed.
By dating the zircons, geoscientists can construct a timeline tracing the development of Earth’s magnetic field.
The strength and direction of Earth’s magnetic field change depending on latitude. For example, the…
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