Acosta gneiss radiometric dating accuracy
The event took place at Macalester College in St. The Earth itself is estimated to be just a half-billion years older, so the Acasta gneiss pronounced nice is some of the very earliest crustal rock still existing on Earth's ever-changing surface. The most well-known is the gneiss that's quarried around the town of Morton, Minnesota. We modern humans wouldn't appear for the first time until sometime in the show's last couple hours. Zircon crystals found in the rock's mineral structure trap uranium in their lattices when they form and can act as timekeepers through measuring the decay of the uranium into lead.
The exact origin of that granite is unknown, but its presence indicates continental crust and surface water were probably already present in those very ancient times. Things like naturally occurring radiation can damage or alter them and thus skew the measurements.
To give you a better idea of the vast amount of time we're talking about here, let's first reduce it to a more comprehendible time-frame. The banding and severe swirling evident in the rock indicates that, at some point, it went through a period or periods of high heat and enormous pressure. The exposure is about miles north of the town of Yellowknife in Canada's Northwest Territories. Courtesy Mark Ryan It may interest you to know that Minnesota has its own ancient gneisses exposed in outcrops in the Minnesota River Valley.