One of the defining features of the Earth is plate tectonics, a phenomenon that shapes the planet’s surface and creates some of its most catastrophic events, such as earthquakes, tsunamis, and volcanic eruptions. While some features of plate tectonics was spotted Nowhere else in the solar system, Earth is the only planet we know of with the full range of processes involved in this phenomenon. And all indications are that it began very early in the history of our planet.
So what did he start? At the moment, it is difficult to distinguish between two main ideas based on our limited evidence of the beginning of the Earth. However, a new study of a piece from Australia vigorously defends one of them: heavy impacts that also occurred early in the planet’s history.
Options and Effects
Soon after the Earth’s formation, its crust would have been made up of a relatively even layer of hard rock acting as a blanket over the still molten mantle below. On top of that, there was probably a global ocean because tectonic plates weren’t yet building mountains. In a way, this situation has been transformed into what we see now: the large regions of moving and buoyant crust of the continental plates and the ever-spreading deep oceanic crust formed from mantle material, all driven by heat from the movement of material through the mantle.
The basic explanation for the origin of plate tectonics is simply the assumption that mantle rotation is also what caused the onset of the phenomenon. Explosions above hot spots in the mantle will bring less dense material to the surface, with the added weight pushing more dense material down the mantle. As these processes continue, more supernatants will be brought to the surface over time, expanding some areas into emerging slabs. This explanation has the advantage of showing the process starting with the same factors driving it today—scientists tend to hate having to rely on multiple, distinct explanations.
But they also hate coincidences, and coincidence is beyond the alternative explanation. The first indications of the movement of tectonic plates appeared about 3.8 billion years ago, not long after the formation of the Earth. That period also overlaps with a series of large impacts, called the Late Heavy Bombardment, that hit the solar system’s bodies.
These effects would have saved a lot of energy for the crust, breaking it up and causing local melting. This will allow hot material from both the molten crust and the mantle to penetrate to the surface through volcanoes. The effect is somewhat similar to volcanic eruptions above a hotspot, with less dense material emerging at the surface, but this may occur at multiple locations across the planet over hundreds of millions of years.
Because of the similarities between the two theories and the fact that much of the evidence has been destroyed over the past several billion years, it is difficult to say which one the evidence supports better. But researchers in a new paper claim to have found evidence that the effects are potentially dangerous.
Starting with a bang
The work is based on zircon crystals, which are very stable structures that include Oldest confirmed plots of land. The authors focused on crystals that originated in a part of Australia called the Pilbara Craton. Cratons are the oldest and most stable parts of the continental crust, and tend to form the core of modern continents. Pilbara is one of the two oldest known batons on Earth.
The researchers examined the zircons for indications that they had been modified by geological processes after their formation, which led to their exclusion from further analysis. They also obtained dates for all crystals based on the decay of uranium. Then they focused on two things that told us something about the environment in which the crystals formed. The first relates to looking at the type of rock the crystals were embedded in, which supposedly reflects the environment in which they formed. The second is the fraction of oxygen that was of a particular isotope (18s). This analysis provides some indication of the temperature at which the crystal formed, which is generally related to its depth.
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