Scientists from The Australian National University (ANU) are helping to solve the mystery of the world’s oldest large fossils of strange organisms that grew up to two metres long and lived more than 500 million years ago.

These mysterious organisms, called Ediacara biota, are the world’s oldest known macroorganisms, living 541–575 million years ago.

Lead researcher Ilya Bobrovskiy from ANU said around 541 million years ago there was a transformational event for Earth known as the ‘Cambrian explosion’ of life.

“The ‘Cambrian explosion’ was the beginning of when complex animals and other macroscopic organisms started to appear massively in the fossil record,” said Mr Bobrovskiy, a PhD scholar from the ANU Research School of Earth Sciences.

Since the fossils were first discovered at Ediacara Hills in South Australia in 1942, debate has raged about whether Ediacara biota are our earliest animal ancestors, failed experiments of evolution, giant unicellular organisms, lichen or bacterial colonies.

The fossils analysed in this study were collected from near the Lyamtsa village in Russia.

Co-researcher Associate Professor Jochen Brocks said the team developed a new technique to study these fossils by extracting molecules from the organic remains.

“The molecules tell us that one of the Ediacara biota fossils, Beltanelliformis, was not an animal, but rather a colony of photosynthetic bacteria,” said Dr Brocks from the ANU Research School of Earth Sciences.

“This is just the beginning. We can now apply the same approach to figure out the nature of other organisms of the Ediacara biota.”