New research reveals that the emergence of life on Earth did not require plate tectonics.
A groundbreaking study published in Nature on June 14 has challenged the long-held belief that plate tectonics is a prerequisite for the emergence of life on Earth. The research, titled “Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism“, unveils a lack of plate tectonics between 3.9 and 3.3 billion years ago, the time when life on Earth originated. “This research encompasses scientific disciplines such as early Earth processes, Archaean geology, zircon geochronology, palaeomagnetism, and the emergence of life on Earth”. Says post-doctoral researcher and co-author Dr Jaganmoy Jodder, based at the Evolutionary Studies Institute, University of the Witwatersrand, South Africa.
As a fundamental theory of geology, plate tectonics, the movement of Earth’s rigid outer shell, has been considered essential for facilitating heat transfer and enabling geological activities crucial for life. However, Professor John Tarduno, the William R. Kenan, Jr. Professor of Geophysics, based at the University of Rochester, United States of America, who is the lead author of the study, remarks, “There has been the assumption that plate tectonics is necessary for life, but this new research challenges that longstanding view.”
The researchers focused on detrital zircon grains from the Barberton Greenstone Belt in South Africa. Zircon crystals are rare minerals that act as time capsules, preserving information about Earth’s magnetic field from billions of years ago. They made a remarkable discovery by analysing the detrital zircon grains’ “palaeointensity” values, a measure of ancient magnetic field strength. Tarduno and co-authors observed that during the investigated time period of Hadean to Palaeoarchaean, Earth did not experience mobile plate tectonics but instead exhibited a phenomenon called a stagnant lid regime, where heat was released differently.
In other words, stagnant lid tectonics is characterized by a solid, immobile crust covering the planet’s surface, lacking distinct plate boundaries and horizontal movement. In this scenario, heat transfer occurs through conduction and cracks in the crust, resulting in less efficient heat transport and limited crustal recycling. Although not as effective as plate tectonics, stagnant lid tectonics can still lead to continent formation.
The findings suggest that while plate tectonics is crucial for sustaining life on Earth, it is not an absolute requirement for the emergence of microbial life on planets similar to ours. Professor Tarduno notes, “Our data suggests that when we’re looking for exoplanets that harbour life, these planets do not necessarily need to have plate tectonics.”
This discovery holds significant implications, as the ancient zircon record is scarce. “Earth’s initial geologic record remains scanty. Only a few places on Earth preserve rocks that have not undergone significant deformations over several billion years throughout their geologic ancestry. Such ancient rocks are found in Archaean cratons, namely the Kaapvaal, Pilbara and Singhbhum cratons. Furthermore, ancient zircon grains that are as old as ~ 4.0 Ga are rare to find. And these have only been reported from South Africa, Australia and India so far”, says Jaganmoy.
By studying these tiny, rare detrital zircon minerals, we gain insights into Earth’s early geological history and the immense forces that have shaped our planet over billions of years”, Jaganmoy says. “It also paves the way for further research by astrobiologists and geobiologists, providing valuable information to evaluate conditions on early Earth and investigate similar environments elsewhere.
The study highlights the complex nature of Earth’s evolution and challenges the assumption that plate tectonics is the only path to habitability. By delving into the secrets these minuscule zircon crystals hold, we understand our planet’s origins and the potential for life beyond the boundaries of plate tectonics. “This is an exciting time to study early Earth conditions because it defines conditions for the origin of life and therefore is the foundation for research on planets/moons by astrobiologists and geobiologists elsewhere. For example, Enceladus, a moon of Saturn, harbours a “soda ocean” with phosphorus, a key element for life. In fact, “the report of phosphorus was published in another Nature article on the same day,” says Jaganmoy, highlighting the close relationship between discoveries about the early Earth and planetary geology, all aimed at understanding the origin and potential for life in the Solar System.
Main photo credit: University of Rochester illustration / Michael Osadciw