On Earth, long-term geochemical cycling facilitated by plate tectonics is argued to be the most significant factor for habitability. Plate tectonics allows heat to move from the mantle into the crust and for nutrient cycling, creating a habitat conducive to life. Plate tectonics is also critical for the long-term stability of liquid water at the surface. Plate tectonics and life appear to be so intertwined that it has been suggested that the origin of life depends on plate tectonics and that the lack of plate tectonics on other planets indicates a lack of life. This hypothesis extends to the search for habitable planets in exoplanet surveys. Recently, however, life’s requirement of plate tectonics has been challenged.
A recent study led by John Tarduno of the University of Rochester and colleagues asked a simple question: does the emergence of life require plate tectonics? The team examined primary magnetite inclusions, which formed within grains of the mineral zircon, and recorded Earth’s magnetic field at the time of formation from some of the oldest exposed regions on the planet, South Africa’s Barberton Greenstone Belt and Jack Hills in Western Australia. These zircons, dated to approximately 3.9–3.4 billion years, showed no change over this period in magnetic field strengths or orientations, both of which would be expected to have occurred on a planetary surface that is in motion due to plate tectonics. Multiple locations showing stable magnetic field orientations and strengths strongly indicate an immobile surface, or stagnant lid tectonics. Yet, despite this, the rock record shows the proliferation of life during this time. These results indicate that life may not need plate tectonics to emerge, though long-term habitability may still require plate tectonics. This implies that the search for habitable exoplanets may need to be substantially expanded to include planets that do not strictly mimic the current Earth. READ MORE