Earth may be younger than previously believed

Posted by Emma Woollacott

Creationists still won't like it, but a new study indicates that the Earth is rather younger than previously believed - up to 70 million years younger, says the team.

An international team used geochemical information from the Earth's mantle and compared it with similar data from meteorites to create a new set of models for the planet's creation.

The results suggest that the length of time between the formation of the solar system, about 4.567 billion years ago, and the point at which the Earth reached its present size, may have been far longer than believed.

Scientists have typically suggested that the Earth's development -  known as 'accretion' - happened over the course of 30 million years. It involved a series of collisions between dozens of smaller planetary bodies.

Now, however, the researchers argue that while the Earth probably grew to 60 percent of its size relatively quickly, the process may well have then slowed, taking about 100 million years in all.
 
"One of the problems has been that scientists usually presume Earth's accretion happened at an exponentially decreasing rate," co-author Dr John Rudge from the University of Cambridge, said.

"We believe that the process may not have been that simple and that it could well have been a much more staggered, stop-start affair."

The team used information taken from isotopes of elements which would have undergone radioactive decay while accretion was happening, to create a set of mathematical models revealing the different ways in which accretion might have occurred.

These geochemical signatures were compared with those of chondritic meteorites, the same age as the solar system.

Dr Rudge modelled every single way in which the Earth could have undergone a process of accretion while matching the hafnium-tungsten and uranium-lead observations. The team never presumed that accretion happened at any particular rate.

While a wide variety of options emerged, the modelling process showed that the Earth almost certainly could not have formed within 30 million years.

Instead, the results suggested that the planet initially grew very quickly, reaching two-thirds of its size within about 10 to 40 million years. Accretion then slowed down, however, and took perhaps another 70 million years to complete.

"If correct, that would mean the Earth was about 100 million years in the making altogether," Dr Rudge said. "We estimate that makes it about 4.467 billion years old - a mere youngster compared with the 4.537 billion-year-old planet we had previously imagined."