The moon came into being with a big bang
Geochemists at the University of Michigan have made the most accurate estimate of the age of our Moon yet. They have found that the moon formed later in the solar system than many scientists previously thought: in all likelihood due to Earth's collision with another planet at least the size of Mars. According to Alexander N. Halliday, professor of geological sciences at the University of Michigan, the "big bang" between Earth and another object happened about 50 million years after the formation of our solar system.
In a study published in Science (November 7 issue), University of Michigan scientists Der-Chuen Lee and Halliday and Gregory A. Snyder and Lawrence A. Taylor of the University of Tennessee how they analyzed tungsten isotopes in rock samples from the lunar surface to unravel the mysteries of our moon's origin. “According to our data, the moon was formed about 4.52 to 4.50 billion years ago. The isotopic composition of tungsten supports the hypothesis that the Moon originated either from Earth itself or from a large object that collided with Earth and had a similar chemical composition,” Halliday said.
"Simulations of the gigantic collision indicate incredibly high temperatures in excess of 10,000 Kelvin, which led to the mixing and merging of rocky material throughout young planet Earth," explained Der-Chuen Lee. "The heat and energy at the moon's formation were also responsible for the production of its magma oceans."
Scientists believe that the planets in our solar system formed about 4.57 billion years ago from a massive cloud of interstellar gas, dust and debris. Earth and other rocky planets in the inner Solar System gradually evolved over millions of years as their gravitational forces pulled larger and larger chunks of material out of the cloud.
Halliday and Lee studied extremely small amounts of tungsten isotopes in 21 lunar samples. To do this, they used what is known as plasma mass spectroscopy (ICP-MS). "Because hafnium-182 decays to tungsten-182 with a half-life of 9 million years, you can use their isotopic ratios to determine the relative ages of materials," Halliday said.
(see also Origin and Development of the Moon in Spectrum of Science 9/94, page 58)
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