Diamonds travel at 60 km per hour inside Earth.
Rising magma in Earth's mantle is thought to ascend at just a few centimetres per year.
It was known that kimberlite, which often contains diamonds, can rise more quickly near the surface, but its speed at great depths was unclear.
And now, Masayuki Nishi and colleagues at Kyushu University in Fukuoka, Japan, have used the mineral garnet as a speedometer.
Garnet inclusions that form inside diamond are stable at depths of between 400 and 700 kilometres, but partially degrade at lower pressures and temperatures.
The researchers synthesised garnet in heated, pressurised containers and measured how fast it degraded as the temperature and pressure were lowered, simulating ascent through Earth's mantle.
And the rate of decay suggested that for a garnet-infused diamond to reach the surface it must take between hours and days to travel from a depth of 400 km.
A rapid ascent mechanism may exist at greater depths than ever thought, New Scientist quoted Nishi as saying.
The study was published in Geophysical Research Letters. (ANI)
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