Geological dating radioactive elements
They have clearly fallen to Earth from outside, often gouging out huge craters such as that called New Québec (61°17´ N, 73° 41' W).Rubidium-strontium, potassium-argon, uranium-lead and samarium-neodymium dating all show that the meteorites formed about 4.6 billion years ago.This uniformity demonstrates that the principle is reliable.When disturbed rocks are studied, the different techniques may give different readings, and much research has been carried out on how to interpret such results.The Earth certainly must be older than the oldest terrestrial rocks found.Samuel Bowring, now of the Massachussetts Institute of Technology, and his coworkers Ian Williams and William Compston of the Australian National University at Canberra have shown that a small area of metamorphic rock in northern Canada, known as the Acasta gneiss, is the oldest known intact solid piece of the Earth's crust.It has even been possible to work out a time scale of the reversals of the Earth's magnetic field.
Those rocks available for analysis (ie, the oldest ones) have been heated and squeezed many times in their GEOLOGICAL HISTORY, because for billions of years continents have been drifting over the Earth's surface, colliding and producing mountains and new ocean floors.The vast majority of atoms (each composed of a nucleus surrounded by electrons) are stable. Because of this particle emission, the original radioactive parent atom changes its identity, becoming a different, stable daughter atom.This change takes place at a known rate determined by the half-life; ie, the time required for one-half of the original number of radioactive atoms to convert to the stable daughter product.Since 1950, radiometric methods have been developed to a very sophisticated level in several countries, including Canada.It has been demonstrated that when rocks which have led an undisturbed history are analysed, all methods reveal the same age.
Two approaches have been developed to circumvent these problems.