Scientists have discovered the oldest known rocks.  Researchers say the finding will offer clues into the formation of the Earth's crust early in the planet's development.  VOA's Jessica Berman reports.

The rocks - dated between 3.8 and 4.25 billion years old - were taken from an expanse of bedrock on the eastern shore of the Hudson Bay in northern Quebec, the Nuvvuagittuq greenstone belt.

They were analyzed by scientists at McGill University in Montreal and the Carnegie Institution's terrestrial magnetism department in Washington D.C.  They concluded the rocks were 250 million years older than previous rock samples.

Jonathan O'Neil is a student at McGill who helped analyze the rocks.  He says the Earth is about 4.6 billion years old, about 300,000 years older than the oldest discovered rock.  

In an interview with the editors of Science, which published a paper on the discovery, O'Neil says the extremely rare rocks should offer invaluable clues as to the formation of the Earth's early crust.

"If you want to study the primordial crust, or how the first crust formed, we actually need to have terrain," he said. "We need to have rocks of that age.  And they are pretty rare.  So the idea is to identify and have these old rocks and then when we confirm the age, now we can start to ask questions, "Okay, are these rocks different?  Did the crust back then, did it form exactly like how the crust forms today?"

Experts say ancient rocks are extremely rare because the primordial crust was crushed and recycled into the Earth's interior many times by plate tectonics, the movement of the planet's early crust that led in the formation of continents.

Scientists say geologists have found older mineral grains called zircons in Western Australia.  The oldest zircon was dated to 4.35 billion years.   

Experts say a mineral analysis of the oldest of the rocks suggests it was made of ancient volcanic deposits.