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Earth started out as 'candy floss'

By Martin Leggett - 28 Mar 2011 11:51:0 GMT
Earth started out as 'candy floss'

As building blocks go, fragile candy floss-like collections of grains hardly seem an ideal starting point for making a planet. But according to research from the Imperial College London, that's exactly the sort of material that was floating in the ether - as the Earth gathered herself together. The work, published in the latest issue of Nature Geoscience, was made possible by extremely detailed mapping, using an electron microscope, of the tiny grains making up ancient meteorites.

The meteorites being studied are some of the oldest objects in the solar system - some 4.6 billion years old. They are called carbonaceous chondrites, and are thought to have formed as precursors to larger asteroids and planets. At that time, when the solar system was literally being born, a swirling disc of dust and gas, called the solar nebula, circled a proto-sun.

The team, led by Dr Phil Bland from the Department of Earth Science and Engineering at Imperial College London, were seeking a better understanding of the fine structure of these most primitive of meteorites. Chondrites are noted for being made up of millimeter-sized round inclusions - called chondrules. These are thought to have formed from semi-molten droplets of rock. They are set in a fine ground-mass of micrometer-sized dust grains, which give the chondrites their characteristic black-speckled appearance.

But the high resolution of the electron microscope, using a technique called electron back-scatter diffraction, allowed to team to probe into how the material, making up these meteorites, came together in the first place. They found that the surface of each drop-like chondrule was evenly-coated with the very fine dust grains. This strongly suggested the droplets were being subjected to shocks as they floated in space - which reinforces the idea of the solar nebula as a swirling turbulent cloud.

The six-strong team were also able to work out in detail the compression that the materials in the meteorite had suffered. From that they could work back to find out the original structure, before it was 'squashed'. This showed that these very first aggregates were fine, fragile and porous - and so similar in many ways to candy floss. That tallies with theories and computer models suggesting that it was the turbulence of the early nebula that compressed this delicate matter into the solid meteorites we see today.

Dr Bland concluded ''What's exciting about this approach is that it allows us - for the first time -to quantitatively reconstruct the accretion and impact history of the most primitive solar system materials in great detail. Our work is another step in the process helping us to see how rocky planets and moons that make up parts of our Solar System came into being.''