The International Commission on Stratigraphy says it has revised the date of the start of Earth's prehistoric Quaternary Period by 800,000 years.

The London-headquartered commission -- the authority for geological science -- decided to end decades of controversy by formally declaring when the Quaternary Period started. The Quaternary age covers both the ice age and moment early man first started to use tools.

Researchers said Earth's history during the 18th Century was split into four epochs, Primary, Secondary, Tertiary and Quaternary. Although the first two have been renamed Paleozoic and Mesozoic, in that order, the second two have remained in use for more than 150 years.

"It has long been agreed that the boundary of the Quaternary Period should be placed at the first sign of global climate cooling," said University of Cambridge Professor Philip Gibbard, a commission member. "What we have achieved is the definition of the boundary of the Quaternary to an internationally recognized and fixed point that represents a natural event, the beginning of the ice ages on a global scale."

In 1983 the boundary was fixed at 1.8 million years, a decision which sparked argument since that point had no particular geological significance.

"For practical reasons such boundaries should ideally be made as easy as possible to identify all around the world. The new boundary of 2.6 million years is just that," Gibbard said.

The decision is detailed in the Journal of Quaternary Science.