In the beginning God created the sponge

IT is a discovery that would have set the mind of Charles Darwin at rest.

When the great naturalist was forming his famous theory of evolution, he puzzled over the lack of evidence for the most primitive forms of life.

Fossils only existed for relatively complex creatures that appeared during an explosion in life about 530 million years ago, during the Cambrian period.

Now scientists say they have discovered the missing link in the chain of evolution. They have found evidence of the oldest animal life yet discovered on Earth – ancient sponges that lived 635 million years ago.

Darwin always believed life developed from biologically basic organisms, such as sponges, which he put at the bottom of his famous Tree of Life.

However, he was puzzled by the lack of evidence for the most simple lifeforms.

Now a team led by Scottish scientist, Dr Gordon Love, from the University of California, has found evidence of very basic organisms that lived about 100 million years before the Cambrian period.

Dr Love said: "Darwin had his so-called dilemma. He couldn't understand why we would see this Cambrian explosion – the appearance of all these animal forms – but nothing earlier. He thought there must be huge chunks of fossil evidence missing. He was puzzled.

"Now, as we have started to celebrate his legacy, we have shown his gut instinct was correct."

Dr Love agreed the discovery could have put the great scientist's mind at rest.

His team found chemical evidence for tiny sponges, dating back to the end of the last major ice age, known as the Marinoan glaciation. The sponges would have lived in the shallow water of the sea off Oman.

The discovery suggests the ocean basins at that time contained enough dissolved oxygen to support simple lifeforms. The organisms would have been similar to modern sponges, which now line seabeds across the world, but they would have been far smaller.

Just enough oxygen would have existed in the shallow areas of the sea for them grow to a few millimetres in size, whereas today sea sponges can measure metres across.

Finding evidence of early forms of life lacking shells or skeletons is not an easy task.

One answer, used by Dr Love's team, is to look for chemical biomarkers which the animals would have left behind.

It was these "chemical fossils" that the scientists found in Oman. Dr Jochen Brocks, of the Australian National University, Canberra, said Dr Love's research was "compelling evidence" of the rise of the sponge lineage before 635 million years ago, which helped to vindicate Darwin.

He said: "Charles Darwin was famously sceptical about the sudden appearance of fully formed animals in the early Cambrian fossil record, beginning some 542 million years ago.

"To a degree, he has been vindicated by the discovery of animal and animal-like fossils extending throughout the preceding Ediacaran period, which followed the end of the second of the great Cryogenian ice ages, 635 million years ago."

Letter that was the genesis for Darwin's evolution idea

A LETTER sent by Charles Darwin to James David Forbes, a college principal at St Andrews University over 150 years ago, forms part of an exhibition to mark the 200th anniversary of the father of the theory of evolution's birth.

In the document, sent in October 1844, Darwin tells Forbes – an eminent Scottish scientist in the field of glaciology – of his observations of parallel lines and the effects of glacial ice.

From 1859, Mr Forbes was principal of the United College of St Salvator and St Leonard at the University of St Andrews.

The exhibition is the centrepiece of events at the university including a series of lectures, on "Darwin Day", 12 February. Academics from across the university will gather to celebrate the bicentennial of Charles Darwin and 150 years of On the Origin of Species.

"On the track of the Beagle", one of the highlights of the event, will be delivered by leading maritime historian Dr Robert Prescott.

Dr Prescott will detail his exploration to discover the final resting place of the ship, aboard which Charles Darwin began to formulate his influential theory of evolution.

Valentina Islas, the event organiser, said: "This brings together some of the greatest minds in the university to celebrate and appropriately honour one of Britain's best known and respected scientists."