The activity of plate tectonics has been blamed for earthquakes and major tsunamis for as long as the idea, first put forth in 1912 by meteorologist Alfred Wegener, has been around.
Subduction forces have erased entire continents over the 3.2 billion years plate tectonics have been occurring on our 4.5-billion-year-old Earth. The planet's crust is shoved down into the inner layers of the Earth's hot mantle, where annihilation awaits.
New research contends that the source of so much destruction is also the source of life. See, behind these apocalyptic-feeling events is something critical to life as we know it: Researcher Rajagopal Anand argues that the orbital patterns of early Earth may have been essential to making plate tectonics possible.
If we want to find habitable worlds — think of them as new Earths — we may need to consider the larger picture of cosmic planetary motion.
Plate tectonics might be crucial to the formation of life on alien worlds
Earth's plate tectonics are contingent upon mass, the internal viscosity contrast, the availability of liquid water, and the heat coming from the planet's core. But the initial rotational velocity, in addition to the revolutionary periodicity of our planet as it moves around the sun, is crucial for plate tectonic activity to commence, according to Anand.
"The initial orbital conditions of the Earth were significantly influenced by the diametrical processes of core segregation and moon formation, and that had probably led to the eventuality of initiation and persistence of plate tectonics," proposes the paper.
With a contrast in viscosity between layers of the planet, an intense heat source, and the availability of liquid water, the motion up and down of mantle (called mantle convection) all interact to give movement to the plates of a rocky planet's crust. But for this motion to continue, the rocky body has to rotate on its axis and rotate around its star in a specific way to achieve habitable conditions.
Here on Earth, its unique orbital conditions were altered substantially, millions of years after the solar system formed, when the moon came into being following a cataclysmic impact with another small planet.
Adding a term to the equation for life in the universe
This impact is thought to have sped up Earth's rotational velocity from its initial rotational speed. And, that — in conjunction with the moon separation process, which is still happening (for example, tidal forces are gradually slowing down the spin of the Earth) — have "far-reaching implications for the initiation of plate tectonics and the emergence of life," writes Anand.
Plate tectonics provides essential initiators for life — a changing crust of the planet is one — and the development of the hydrosphere and an atmosphere.
The changing shape of the crust also provides new sources and sinks for sedimentation processes that circulate nutrients for the evolution and diversity of organic life.
The researchers found that optimal conditions of the rotational and revolutionary periodicities are essential for the development of plate tectonics.
At least, they may have been on Earth. And if this is the case, it could help solve one of the necessary conditions for habitable conditions on alien worlds beyond our solar system.
Europa, Mars, and Venus lack the parameters for life as we know it
Europa is tidally locked to its host planet, Jupiter. This relationship precluded the development of plate tectonics since the gravitational stress on the Jovian moon is uneven. In other words, it could be that Europa, despite its deep oceans, might be short one of the crucial features for organic life to evolve. At least, life as we know it.
Both Mars and Venus have all the ingredients to form long-lived radioactive isotopes, which creates an additional heat source and thus the mantle's convection. Yet, both planets are tectonically "dead with a stagnant lid," according to the study. Things might have gone differently for our closest planetary cousins if orbital and spin velocities had approached the equivalence ratio of rotational periodicity. It approaches a near match to the time it takes for the planet to move one degree in its orbit around the sun.
Extending the parameters for interstellar life — Earth's present-day periodicity of 365 days stacked against its rotational periodicity of 0.997 days has contributed to optimal conditions for plate tectonics. If we're going to find another planet beyond our solar system like ours, we might have more luck looking for a match in orbital parameters.
Other parameters, like Earth's distance from the sun relative to the latter's size, in addition to our planet's distance from enormous gas giants, like Jupiter, are crucial for life.
Humans need to continue working out the unknown terms in the equation that determines how, when, and where life can come into being on alien worlds, if we're ever to learn, for sure, whether or not we're alone in the universe.
The existence of plate tectonics on the Earth is directly dependent on the internal viscosity contrast, mass of the planet, availability of liquid water and an internal heat source. However, the initial conditions of rotational velocity and revolutionary periodicity of the Earth around the Sun too must have been significant for the inception of plate tectonics. The initial orbital conditions of the Earth were significantly influenced by the diametrical processes of core segregation and Moon formation and that had probably led to the eventuality of initiation and persistence of plate tectonics. The change in the orbital conditions could have rendered the Earth to evolve in a near-linear trend so that the rotational periodicity of the planet (TP) could approach the time taken for the planet to travel one degree in its orbit around the Sun (T1degree), that is TP ~ T1degree. Such an optimal condition for the rotational and revolutionary periodicities could be essential for the development of plate tectonics on the Earth. This hypothesis has direct implications on the possibility of plate tectonics and life in extrasolar planets and potentially habitable solar planetary bodies such as Europa and Mars.