Washington, Nov 13 : A new theory has emerged as to how fossils may form, with the finding that 500 million year old fossils in Canada were formed by minerals that were 'stone baked' deep under the Earth's crust.
The finding was made by scientists from the universities of Leicester and Cambridge and from the British Geological Survey, who studied 500 million year-old fossils of the Burgess Shale in Canada, discovered over a century ago.
Once an ancient sea bed, the Burgess shale were formed shortly after life suddenly became more complex and diverse - the so-called "Cambrian explosion" - and are of immense scientific interest.
The beautiful silvery fossils show the true nature of the life of that time, just after the "Cambrian explosion" of animal life.
Yet, their existence is a paradox.
The fossils have been buried deep in the Earth's crust and heated to over 300 degree Celsius, before being thrust up by tectonic forces to form a mountainous ridge in the Rockies.
Usually, such extreme conditions are thought to destroy fossils. But, in the Burgess Shale the most exquisite detail of soft tissues has been preserved.
Normally, only hard parts of ancient animals, like the bones, teeth or shells became fossilized, and soft parts were rarely preserved.
Many plants and invertebrate animals evolved, lived for millions of years and became extinct, but left no trace in the fossil record.
But, the Burgess Shales preserved soft tissue in exquisite detail, and the question of how this came to happen has troubled scientists since the discovery of the fossils in 1909.
Now, by careful restudy of its fossils, Alex Page and his colleagues Phil Wilby, Sarah Gabbott and Jan Zalasiewicz, of the universities of Cambridge and Leicester and the British Geological Survey, have solved this riddle.
They have shown that as the delicate organic tissues of these fossils were heated deep within the Earth, they became the site for mineral formation.
The new minerals, forged at these tremendous depths, picked out intricate details such as gills, guts and even eyes.
According to Alex Page, "This provides a whole new theory for how fossils form. The deep heating may not have cremated them, but it certainly left them stone baked."