Saturday Star

Rock pools that take us back 3.7bn years

- SHAUN SMILLIE

ALONG a stretch of South African coastline are some special rock pools that have become windows into what our world looked like 3.7 billion years ago.

In the rock pools are green mats of what appear to be algae, but they are actually living fossils that date back to when the Earth was young. Their discovery has scientists excited. The green mats are stromatoli­tes, layer upon layer of cyanobacte­ria and diatoms, that live in water with high concentrat­ions of calcium carbonate, and undertake photosynth­esis.

The diversity of bacteria in each of these pools is so great that researcher­s even believe there are new pharmaceut­ical substances to be discovered, including possible anti-cancer drugs.

Stromatoli­tes were considered rare, that was until they were spotted in abundance along the Eastern Cape coast, south of Port Elizabeth.

According to Professor Renzo Perissinot­to, who holds a research chair in shallow-water ecosystems at the Nelson Mandela Metropolit­an University (NMMU), he and his team have so far identified 540 rock pools that hold stromatoli­tes.

These pools, he believes, might explain how the Earth evolved its oxygen-rich atmosphere and provide the reason why our earliest ancestors learnt to move.

The earliest stromatoli­te fossils have been dated to 3.7 billion years and were around at a time when the Earth was a very different place to what it is today.

“It would have been hellish back then,” explains Perissinot­to. “The sky would have been a red or orange, with no oxygen, and seas would have been green because of the high iron content. There was lots of volcanic activity.”

However for the stromatoli­tes, this was a happy time that lasted more than 2 billion years, when conditions were perfect for them and they faced no competitio­n.

But the theory is that their success ultimately led to their downfall.

Vast mats of photosynth­esising stromatoli­tes filled the atmosphere with oxygen which in turn allowed metazoa (more complex and multicellu­lar organisms) to evolve.

These metazoa, the theory goes, bur rowed into the mats and fed on them.

“They would have grazed on them, like cows grazing on a field,” says Perissinot­to.

Stromatoli­te for mations declined sharply, but some survived and have clung on up until the present.

Prominent l iving communitie­s have been found in Wester n Australia, Ireland and the Bahamas.

But the South African stomatolit­es are the most extensive.

“Why it is so exciting is that the structures of the South African stromatoli­tes are very similar to those found in the fossil record,” Perissinot­to says.

In South Africa, stomatolit­es occur where freshwater mixes with seawater in the intertidal area.

But while multicellu­lar organisms have been fingered as being responsibl­e for the downfall of stromatoli­tes, researcher Dr Gavin Rishworth, also of NMMU, has seen behaviour that suggests that it is more complicate­d than that.

He has been investigat­ing rock pools along the Eastern Cape coast and has noticed multicellu­lar organisms living in harmony with stromatoli­tes.

“It didn’t make sense, as it was thought that they would destroy them. We needed to find out why they were coexisting.”

He came to the conclusion that these organisms were using these green mats to hide from predators and to take advantage of the oxygen-rich environmen­t.

It may be a relationsh­ip that goes back hundreds of millions of years and multicellu­lar organisms might be partly off the hook in causing the great stromatoli­te die-off of 500 million years ago.

Perissinot­to believes this offers a glimpse into what was happening all that long time ago.

“What might have happened is that during the day the metazoa took comfort from the stromatoli­tes, with t heir increased oxygen levels, then at night they would go out to feed. And this required them to develop mobility.”

The stromatoli­te downfall, says Perissinot­to, might have come instead from the changing chemistry of the oceans.

But in the future, Perissinot­to, his team and five internatio­nal universiti­es will be delving deeper into the secrets hidden in these rock pools hoping to obtain a better understand­ing of that time when life had just begun.

 ??  ?? STORY TO TELL: Professor Renzo Perissinot­to and his team collect stromatoli­tes from a rock pool close to Port Elizabeth in the Eastern Cape.
STORY TO TELL: Professor Renzo Perissinot­to and his team collect stromatoli­tes from a rock pool close to Port Elizabeth in the Eastern Cape.
 ??  ?? RARE FIND: Green mats are stromatoli­tes, layer on layer of cyanobacte­ria and diatoms, that live in water with high concentrat­ions of calcium carbonate. Usually rare, they are in abundance along a 200km stretch of the Eastern Cape.
RARE FIND: Green mats are stromatoli­tes, layer on layer of cyanobacte­ria and diatoms, that live in water with high concentrat­ions of calcium carbonate. Usually rare, they are in abundance along a 200km stretch of the Eastern Cape.

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