Valley, a University of Wisconsin geoscience professor, led the research team. Writing in the journal Nature Geoscience on Sunday, the team said the discovery indicates that Earth's crust formed relatively soon after the planet formed and that the little gem was a remnant of it. But because some scientists hypothesized that this technique might give a false date due to possible movement of lead atoms within the crystal over time, the researchers turned to a second sophisticated method to verify the finding. They used a technique known as atom-probe tomography that was able to identify individual atoms of lead in the crystal and determine their mass, and confirmed that the zircon was indeed 4. Valley added that these findings suggest that the early Earth was not as harsh a place as many scientists have thought.
Earth's Oldest Crust Dates to 4.4 Billion Years Ago
Earth's oldest crystal found in Australia › News in Science (ABC Science)
Zircons are tiny crystals of zirconium silicate ZrSiO 4 that originate in igneous rock, which forms when volcanic magma cools. Zircon is harder than quartz and almost as hard as diamond. Because of these characteristics, zircon is the mineral most frequently used in various radioisotope dating methods for dating rocks assumed to be at least a few hundred million years old. Its ability to retain impurities within its crystal lattice is very important in establishing the validity of these dating methods. As they decay, they produce helium and cause defects in the crystal due to radiation damage. Each uranium atom produces eight helium ions through its decay chain, and each thorium atom produces seven helium ions.
Zircon study questions dates for cataclysms on early Moon and Earth
How old are you? How old are your grandparents? Do you know how old Canada is? Or the pyramids in Egypt?
What was missing from the early geologic time scale? While the order of events was given, the dates at which the events happened were not. With the discovery of radioactivity in the late s, scientists were able to measure the absolute age , or the exact age of some rocks in years. Absolute dating allows scientists to assign numbers to the breaks in the geologic time scale. Radiometric dating and other forms of absolute age dating allowed scientists to get an absolute age from a rock or fossil.