Moon Found to Be About 4.5 Billion Years Old

The moon’s age is finally getting pinned down.

Of course, age is relative in a universe billions of years old. A new study narrows the moon’s age down to a 20-million-year range.

Using a new tool to study lunar rocks, University of Michigan scientists have narrowed the time of the moon’s formation to between 4.52 billion and 4.5 billion years ago.

Scientists believe the planets in our solar system began forming about 4.57 billion years ago.

“People have come up with ages for rocks on the moon previously, but they’ve been rather imprecise. What we’ve done is pin down the age of the moon rather precisely,” geological sciences professor Alexander Halliday said.

Research by Halliday, his colleague Der-Chuen Lee and two University of Tennessee scientists also backs up the “giant impact” theory of how the moon was created.

“The basic idea is that a planet about the size of Mars or perhaps even larger hit the Earth with a glancing blow,” Halliday said.

The lunar rock studies suggest that the moon was formed from material from the Earth, from the planet that hit Earth or from a combination of the two.

If the moon came from the planet that hit Earth, that planet’s composition had to have been similar to the Earth’s composition, Halliday said. The giant impact would have occurred about 50 million years after the start of our solar system.

Research was done on 21 moon rocks using a recently developed method to analyze lunar samples. The equipment is capable of analyzing extremely small samples: in this case, less than a millionth of a gram of tungsten.

Tungsten is a metal. The study looked at one isotope, or form, of tungsten.

Measurements of the tungsten isotope in moon rocks gave results that suggest when the moon would have formed, Halliday said.

The work at Michigan and by Tennessee researchers Gregory Snyder and Lawrence Taylor looked at several types of moon rocks, said Larry Nyquist, manager of the Thermal Ionization Mass Spectrometry Laboratory at NASA’s Johnson Space Center at Houston.

“It’s a very interesting discovery and something we have to try to factor into our own measurements,” he said.

There are four major theories about how the moon formed:

* Co-accretion: The moon formed in the same place and of the same materials as the Earth.

* Fission: The moon is a chunk of the Earth that was broken away from the planet and was propelled into orbit by an asteroid impact.

* Giant impact: The moon was a Mars-size rock that hit the Earth; a large part, perhaps in the form of molten rock, ricocheted into an orbit about the planet.

* Capture: The moon was a huge rock that wandered into Earth’s gravitational grasp and was captured in the planet’s orbit.