Earth is the only known planet that has complex organics, and this ability is partially
The new study uses zircons - the mostthe oldest minerals ever discovered on Earth to provide a glimpse into the planet's ancient past. The oldest zircon in the study, which was sourced from Jack Hills in Western Australia, was about 4.3 billion years old, which means that these nearly indestructible minerals were formed when the Earth itself was in its infancy for only about 200 million years. Along with other ancient zircons collected in Jack Hills in the earliest history of the Earth up to 3 billion years ago, these minerals are the closest researchers to continuous chemical records of the nascent world.
"We reconstructed how the Earth went from a molten ball of rock and metal to what we have today.None of the other planets, continents, liquid oceans, or life.In a sense, we're trying to answer the question of why Earth is unique, and we can answer that questionquestion with the help of these zircons."
Michael Ackerson, research geologist at the Smithsonian National Museum of Natural History
To look into the past of the Earth for billions of years,A team of researchers collected 15 grapefruit-sized stones in Jack Hills and ground them down to their smallest constituents, grinding them into sand. Fortunately, zircons are very dense, so it is relatively easy to separate them from the rest of the sand using a technique similar to gold washing.
The team tested over 3,500 zircons, eachjust a couple of human hairs wide by blowing it up with a laser and then measuring their chemical composition with a mass spectrometer. These tests revealed the age and chemical composition of each zircon. Of the thousands tested, about 200 were studyable due to the ravages of the billions of years these minerals have endured since their inception.
The age of zircon can be determined with a highdegree of accuracy, since every zircon contains uranium. The known radioactive nature of uranium and the well-defined decay rate allow scientists to reconstruct the lifetime of this mineral.
The research team was also interested inaluminum content in each zircon. Tests of modern zircons show that zircons with a high aluminum content can only be obtained in a limited number of ways, allowing researchers to use the presence of aluminum to infer what might have happened, geologically speaking, during the formation of the zircon.
After analyzing the results of a study of hundredsOf the thousands of useful zircons tested, scientists found a marked increase in aluminum concentration around 3.6 billion years ago. Ultimately, they concluded that rocks are melting deeper below the Earth's surface, which means that the planet's crust is getting thicker and begins to cool, and that this thickening of the earth's crust was a sign that a transition to modern plate tectonics is taking place.
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