Scientists know that plate tectonics — the movement of the uniquely rigid plates that make up the Earth’s crust — form continents and mountain ranges and are critical to the evolution of the Earth’s surface from lava and rocks to habitable environments. But we don’t know when it started . A team of scientists led by Harvard University has analyzed some very rare ancient crystals called zircon, the size of a small grain of sand and almost indestructible, for chemical clues that plate tectonics began. The study, published in the journal AGU Advances , shows that 3.8 billion years ago, the geochemical properties of these zircones changed significantly, making them look more like zirconium formed today in the hot environment where plate tectonics take place stone. Think of zircon as tiny time capsules that retain chemical clues from Earth’s first 500 million years. Some formed in Earth’s magma more than 4 billion years ago, when Earth was still in its infancy, geologically speaking. This makes them the oldest known material on Earth. Their secrets can be learned by illuminating them with laser light, which is exactly what the researchers used in their analysis.
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