Scientists have discovered that the earth may be significantly younger than previously believed – by 70 million years.
The solar system was formed 4.567 billion years ago, but the Earth reached its present size much later through a process known as ”accretion”.
It was previously estimated that it took around 30 million years for the Earth to accumulate to its present size – making it 4.537 billion-years-old.
But new research has revealed that the process probably took around 100 million years – meaning that the Earth is actually closer to 4.467 billion-years-old.
The international team compared geochemical information from the Earth’s mantle with data from fallen asteroids to create a new set of mathematical models of the Earth’s formation.
Traces of 182-tungsten can be found in both the Earth’s molten core and in the mantle – or crust – which forms the surface of the planet.
Researchers compared the half life of isotopes of Earth tungsten which would had undergone radioactive decay during accretion with isotopes from asteroids which had not.
The ”chondritic” meteorites are primitive bodies which have fallen to Earth recently but never undergone any sort of metal segregation.
By comparing the results, they were able to put together a series of mathematical models recreating various ways in which accretion took place.
Dr John Rudge, research fellow at Trinity College, Cambridge, concluded that the Earth grew to 60 per cent of its size in 10 to 40 million years but then slowed and only reached its full size after 100 million years.
He said: ”If correct, that would mean the Earth was about 100 million years in the making altogether.
”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.”
“The whole issue hinges on working out how long it took for the core of the Earth to form, which is one of the big unknowns in this area of science.”
“One of the problems has been that scientists usually presume Earth’s accretion happened at an exponentially decreasing rate.
”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 Earth was formed by a series of collisions between dozens of smaller planetary bodies or ”planetary embryos”.
Parts of these proto-planets blended together and the intense heat of impact melted their interiors.
Over time, this led to the formation of a molten metal core at the heart of the Earth, with a silicate mantle overlying it.
It is believed that the final part of the process happened when a body the size of Mars collided with the Earth and caused a part to break away forming the Moon.
The study – ”Broad bounds on Earth’s accretion and core formation constrained by geochemical models” – appears in the latest issue of Nature Geoscience.
