How did iron become scattered throughout Earth 's 2,000-mile ( 3,200km ) thick mantle more than four billion years ago ? That 's a question that has puzzled scientists , with most thinking asteroid impacts were the cause , but now a new theory has been presented - iron rain . By re-analysing the vapourisation point of iron , a study has determined that conditions on early Earth would have caused iron to rain down on the ground . Scientists in New Mexico have a new theory for the origin of Earth 's iron . Research suggests iron would have turned into vapour when meteorites hit the young Earth , as shown in the artist 's impression above . The vapour would then have drifted up in plumes , condensed and then rained down on the surface of our planet . The research was conducted with the Z machine at Sandia National Laboratories in Albuquerque , New Mexico . The machine is the most powerful producer of pulses of electrical energy on Earth . By studying the shock pressure required to vapourise iron , they found the value was 40 per cent less than previously thought . Astrophysicists say this lower pressure - 507 gigapascals ( GPa ) compared to 887 GPa - was easily achieved during the latter stages of Earth 's formation . 'Because planetary scientists always thought it was difficult to vapourise iron , they never thought of vapourisation as an important process during the formation of Earth and its core , ' said principal investigator Dr Rick Kraus . The researchers created a target - consisting of an iron plate 0.008in ( 5mm ) square and 200 microns thick - against which they launched aluminum flyer plates travelling up to 16 miles ( 25km ) per second . At this impact pressure , the powerful shock waves created in the iron cause it to compress , heat up and vapourise . The results showed that the vapourisation threshold for iron is 40 per cent lower than previously thought . 'But with our experiments , we showed that it 's very easy to impact-vapourise iron . ' The result of this would have been that a solid piece of iron , after impacting Earth perhaps as part of an asteroid , would disperse into an iron vapour due to the force of the impact . Earth is thought to have been pummelled by asteroids during the Late Heavy Bombardment period , 4.1 to 3.8 billion years ago . Forming clouds across the surface , the vapour would then rain down onto the ground and mix with the mantle , which was molten at the time . 'This changes the way we think of planet formation , in that instead of core formation occurring by iron sinking down to the growing Earth 's core in large blobs ( technically called diapirs ) , that iron was vapourised , spread out in a plume over the surface of Earth and rained out as small droplets , ' said Dr Kraus . 'The small iron droplets mixed easily with the mantle , which changes our interpretation of the geochemical data we use to date the timing of Earth 's core formation . ' The research , which found iron vapourised at values 40 per cent lower than thought , was conducted with the Z machine ( pictured ) at Sandia National Laboratories in Albuquerque , New Mexico . The machine is the most powerful producer of pulses of electrical energy on Earth . In previous theories , it was thought that iron arrived from collisions between Earth and planetesimals - rocks ranging in size from several metres to hundreds of kilometres in diameters . This would have happened in Earth 's late formative stages more than four billion years ago , with the iron being sent bullet-like into the region between the core and crust - the mantle . But if that were true , then the moon would also have similar amounts of iron in its mantle , as it underwent the same bombardment - but this does not appear to be the case . This led the scientists to their new conclusion - and they add that the moon 's gravity would have been too weak for it to have held onto iron rain-bearing vapour , like Earth . This accounts for the lack of iron seen scattered in the moon 's mantle . According to the scientists , the moon 's gravity would have been too weak for it to have held onto iron rain-bearing vapour , like Earth , during the Late Heavy Bombardment period ( artist 's impression of moon shown ) . This accounts for the lack of iron seen scattered in the moon 's mantle .
Scientists in New Mexico have a new theory for origin on Earth 's iron . Previously it was unclear how iron was scattered throughout the mantle . But research suggests the vapourisation point of iron is lower than thought . This means it would have turned into vapour when rocks hit early Earth . It would have drifted up in plumes and then rained down on the surface .