How does radioactive dating help determine the age of fossils
The evolution of this planet and its atmosphere gave rise to life, which shaped Earth's subsequent development.Our future lies in interpreting this geologic past and considering what changes--good and bad--may lie ahead Like the lapis lazuli gem it resembles, the blue, cloud-enveloped planet the we recognize immediately from satellite pictures seems remarkably stable.Panning for zircons ISOTOPE GEOLOGY has permitted geologists to determine that the accretion of Earth culminated in the differentiation of the planet: the creation of the core--the source of Earth's magnetic field--and the beginning of the atmosphere. Patterson of the California Institute of Technology used the uranium-lead clock to establish an age of 4.55 billion years for Earth and many of the meteorites that formed it.In the early 1990s, however, work by one of us (Allègre) on lead isotopes led to a somewhat new interpretation.At that time--4.44 billion to 4.41 billion years ago--Earth began to retain its atmosphere and create its core. The emergence of the continents came somewhat later.
Nevertheless, in recent decades, several important nds have been made, again using isotope geochemistry.
Such constant change has characterized Earth since its beginning some 4.5 billion years ago.
From the outset, heat and gravity shaped the evolution of the planet.
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.
Consequently, the number of collisions between planetesimals, or meteorites, decreased.