Premature birth of Earth

Blue planet: Its core took 30 million years to form

The Earth formed more quickly than we thought.

Scientists think it took shape about 30 million years after the birth of the Solar System.

The formation of the Moon must have occurred during the first 30 million years of the life of the Solar System

Until now, its core was thought to have arisen over the course of 60 million years.

The evidence comes from revised radioisotope dating of meteorites, the remnants of the stuff that made the planets.

The data also has implications for the genesis of the Moon.

The Moon was thought to have arisen after an impact between the burgeoning Earth and a planet at least as massive as Mars.

Smashing impact

One theory is that the Earth was half-made when it collided twice with a body double the mass of the Red Planet.

The research has implications for how the Moon formed

Another assumes it was about 90% of its current dimensions when it was struck by a Mars-sized object.

Both collisions could, in theory, have produced a big enough impact to blast enough debris into space to form the Moon.

But since the Earth took 100 million years to reach something like its present size, the first option is more likely, according to two research teams, from Germany and the United States.

'Core formation'

The data is based on measurements of radioactive nuclei in meteorites.

The ratio of the radioactive elements hafnium and tungsten in these very primitive rocks was compared with rocks on Earth and Mars.

It suggests that previous estimates of how quickly the Earth formed - about 60 million years after the birth of the Solar System - are wrong.

The research, published in the journal Nature, also gives an estimate for the creation of Mars.

The planet, because it is smaller, is thought to have taken about 13 million years to take shape.

"We conclude that core formation in the terrestrial planets and the formation of the Moon must have occurred during the first 30 million years of the life of the Solar System," says the German team, led by T Kleine of the University of Muenster.