The ancient Australian crystals date back to just million years after Earth formed, and have survived tumbling trips down rivers, burial deep in the crust, heating, squeezing and a tectonic ride back to the surface. The Australian zircons , from the Jack Hills, aren't the oldest rocks on Earth — those are in Canada — but about 3 billion years ago, the minerals eroded out some of Earth's first continental crust and became part of a riverbed. Geologists have carefully sorted out more than , microscopic Jack Hills zircons that date back to Earth's early epochs, from 3 billion to nearly 4.
Confirmed: Oldest Fragment of Early Earth is 4.4 Billion Years Old
The planet is 4. The crystals contain microscopic inclusions, such as gas bubbles, that provide a unique window into conditions on Earth as life arose and the first continents formed. Just three of the very oldest zircons have been found, ones that date back to almost 4. Their extreme age always makes the dates suspect, because of possible radiation damage.
7 Oldest Rocks Ever Discovered
The radiation damage means the zircons could have been contaminated during their long lifetime. Zircons hold minute amounts of two naturally occurring uranium isotopes — isotopes are atoms of the same element with different numbers of neutrons. Uranium radioactively decays to lead at a steady rate. Counting the number of lead isotopes is how scientists date the crystals.
But as the uranium kicks out lead atoms, the radioactive decay releases alpha particles, which can damage the crystals, creating defects. These defects mean fluids and outside elements can infiltrate the crystals, casting doubt on any conclusions about early Earth based on the zircons.
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More important, uranium and lead can move around within a crystal, or even escape or enter the zircon. This mobility can throw off the lead isotope count used to calculate the zircon ages, and is the source of the decades-long controversy over the Jack Hills zircons' Methuselah lifespan.
Valley and his co-authors hope to end the debate by showing that even though one of the oldest Jack Hills zircons suffered radiation damage, the lead atoms stayed in place. The researchers painstakingly counted individual lead atoms within the oldest-known zircon with a recently developed technique called atom-probe tomography. Inside the zircon, lead atoms clustered together in damage zones just a few nanometers wide.
Imagine cliques of teens during high school lunch — like teenagers, no lead atoms had left their zones. The key finding, that lead atoms stick close to home inside this primeval zircon, means age estimates based on uranium-lead dating techniques are accurate, the researchers report.
Dating the Oldest Rocks and Minerals in the Solar System | Elements | GeoScienceWorld
Because of the unique environments in the protoplanetary disk, dating the earliest meteorites has its own opportunities and challenges, different from those of terrestrial geochronology. Sign In or Create an Account. Close mobile search navigation Article navigation. Volume 9, Number 1. Previous Article Next Article. Research Article February 01, Elements 9 1: Abstract Meteorites originating from asteroids are the oldest-known rocks in the Solar System, and many predate formation of the planets.
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