World's oldest object offers insight into the Earth 4.6 billion years ago

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The Independent Online

Scientists have turned to crystal-gazing to see a vision of the Earth as it was just after its creation more than four billion years ago.

Scientists have turned to crystal-gazing to see a vision of the Earth as it was just after its creation more than four billion years ago.

A microscopic crystal of zircon - an unusually long-lived mineral - has provided geologists with a rare insight into the state of the world immediately after its creation. Chemical analysis of the crystal, which was formed about 4.4 billion years ago and is the oldest identifiable object on Earth, has overturned conventional views about how the planet formed.

The accepted view of creation is that the Earth formed about 4.5 billion to 4.6 billion years ago from debris left over after the birth of the Solar System and remained little more that a ball of molten rock and metal for millions of years when it was pulverised by meteors.

But the latest research suggests that rather than being a hot, liquid magma, the Earth at that time may have been a relatively cool planet with a solid crust forming rudimentary continents separated by primitive oceans, an international team of scientists say today in the journal Nature.

"This zircon thus represents the earliest evidence for continental crust and oceans on the Earth," says the team, which included Simon Wilde of the Curtin University of Technology in Perth, Australia, who found and dated the crystal, and Professor Colin Graham of Edinburgh University.

Another member of the team, Professor John Valley of the University of Wisconsin in Madison, said the crystal may also undermine the accepted views on the creation of the Moon, which was thought to have resulted from a collision between the Earth and a Mars-sized planet 4.45 billion years ago.

Professor Valley said: "The crystal's early age restricts theories for the formation of the Moon. Perhaps the Moon formed earlier than we thought, or by a different process."

Dating techniques based on the ratio of radioactive isotopes contained within the crystal - which was unearthed from a site in Western Australia - revealed its extreme age.

Zircon crystals are believed to form only under strict chemical conditions, when the mineral and rock in which it developed was wet and at relatively low temperatures.

Professor Valley said: "These results may indicate that the Earth cooled faster than anyone thought. Previously, the oldest evidence for liquid water on Earth, a precondition and catalyst for life, was from a rock estimated to be 3.8 billion years old."

The new dates have repercussions for the origin of life, which may have arisen earlier than previously thought because a cooler, wetter Earth is necessary for biological molecules to survive. The earliest known biochemical evidence for life and for a watery environment is estimated to be 3.85 billion years ago.

Zircon crystals are the only known survivors of the world prior to 4 billion years ago, the so-called geological Dark Ages when the planet came under bombardment from meteors, resulting in an environment too harsh for life or even rocks to survive.

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