The oldest rock ever found in New Zealand has been unearthed in Wānaka by Associate Professor James Scott of Otago University.

The rock is estimated to be more than five times the age of any other rock found in New Zealand.

The piece of peridotite rock is 2.7 billion years old; the previous oldest rocks being trilobite found in Nelson at about 500 million years old.

The rock peridotite was found on the southern shore on Lake Wanaka near Albertburn Station,

This particular rock comes up from an old volcano, Scott said.

“Around Lake Wānaka there are little scraps of old volcanos and some of them, when they erupted magma, as it was coming to the surface it picked up bits of the peridotite and brought it up too”.

These “green rocks" were rare because they had travelled to the surface from a much lower level — from 30km to about 60km below the Earth’s surface.

“I have had a research programme looking at these events across New Zealand and analysed them to establish how old the rock is,” Scott said.

"We now know that New Zealand actually comprises crust and mantle and together these are called the lithosphere."

Peridotite is a green magnesium-rich rock from Earth's mantle, found underneath the continental crust.

Scott had also collected bits of mantle peridotite from the Chatham Islands, the sub-Antarctic Auckland Islands, Fiordland, through East and West Otago, and in Westland.

The dating analyses for the Wānaka find was undertaken at the University of Alberta in Edmonton, Canada,

Peridotite was rare even in Otago, but because of the region’s history of ancient volcanism, it was the best overall region in New Zealand to find the ancient rock, Scott said.

"These small rocks give a unique insight into what lies deep beneath our feet," he said.

Read edition 1005 of the Wānaka Sun here.