Four billion years old are the diamonds that have formed as acicular inclusions in the zirconium crystals. Image: Martina Menneken
In Western Australia, researchers have discovered over four billion years old diamonds. The gems were created at a time when the earth was only about 500 million years old, and thus more than a billion years older than all previously found diamonds. They are enclosed in zircon crystals, the oldest known mineral on earth. Diamonds usually only occur at very high temperatures. The discovery of diamonds thus contradicts the theory that the Earth has already cooled down sufficiently to produce oceans within 200 million years after its formation. Precise analysis of the zirconium crystals and diamonds allowed the researchers to draw conclusions about the origin of their samples. The zirconium crystals thus formed on the earth's surface with the participation of water. The earth must have been so far cooled down at this time that water formed. However, under these conditions, carbon can only form diamond crystals when exposed to extremely high pressures, such as those prevailing over 100 kilometers below the Earth's surface. Nevertheless, the two crystals evidently originated at the same time and in the same place.

According to Menneken, the most probable explanation for this contradiction is that the carbon was incorporated into the zirconium crystals produced on the surface of the earth, not in the form of diamonds but in graphite form. As a result of movements of the mantle and the earth's crust, the zirconium crystals were then pushed very rapidly ever lower towards the center of the earth until the pressure was high enough to cause diamonds to form.

Whether the diamonds really formed in this way, the researchers want to investigate by more detailed analysis of the carbon isotopes in the diamond samples. They hope to find out more about how the earth actually looked during its first 500 million years of life.

Martina Menneken (University of Münster) et al .: Nature, Vol. 448, p. 917 ddp / science.de? Anja Baster's ad

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