Gneiss age dating
Gneiss age dating
These forces were gradually joined by the global effects of the emergence of life.
From the outset, heat and gravity shaped the evolution of the planet.
This undertaking had been considered impossible by founders of geology, including Charles Lyell, to whom the following phrase is attributed: No vestige of a beginning, no prospect for an end.
This statement conveys the idea that the young Earth could not be re-created, because its remnants were destroyed by its very activity.
As Patterson argued, some meteorites were indeed formed about 4.56 billion years ago, and their debris constituted Earth.
But Earth continued to grow through the bombardment of planetesimals until some 120 million to 150 million years later. Geological Survey in Denver two decades ago and is in agreement with Wetherills estimates.
Scientists used to believe the rocky planets, including Earth, Mercury, Venus and Mars, were created by the rapid gravitational collapse of a dust cloud, a deation giving rise to a dense orb.
In the 1960s the Apollo space program changed this view.Dating rocks using so-called radioactive clocks allows geologists to work on old terrains that do not contain fossils.The hands of a radioactive clock are isotopes--atoms of the same element that have different atomic weights--and geologic time is measured by the rate of decay of one isotope into another [see "The Earliest History of the Earth," by Derek York; , January 1993].Consequently, the number of collisions between planetesimals, or meteorites, decreased.Fewer items available for accretion meant that it took a long time to build up a large planet. Wetherill of the Carnegie Institution of Washington suggests that about 100 million years could pass between the formation of an object measuring 10 kilometers in diameter and an object the size of Earth.Continents thus provide a form of memory because the record of early life can be read in their rocks.