From sand to rock—quickly!

by David Catchpoole

If anyone thinks that rocks need millions of years to form, then experiments carried out by Murdoch University (Perth, Western Australia) researchers would surely overturn that idea.

That’s because the researchers have been able, with the help of added microorganisms, to turn sand into stone rapidly.¹

The researchers investigated microbes for their ability to produce a cementing agent (dubbed “biocement”) that would bind sand particles together, forming rock. The bacterium Sporosarcina pasteurii (formerly known as Bacillus pasteurii) has an enzyme that enables it, in the right circumstances, to do just that. Its urease enzyme hydrolyses urea, and when this hydrolysis occurs in a calcium-rich environment, it generates binding calcite cement (calcium carbonate) as a by-product.²

In a series of trials, the bacterium treatment altered the consistency of sand, making soft sand harder, even “changing it into a substance as hard as marble”. According to Dr Ralf Cord-Ruwisch, “The biggest block we have made so far was in a shipping container, just to prove that it can not only work in the laboratory.”¹

With repeated treatment, “we found that it turns harder each time”, said Dr Cord-Ruwisch. “At the very end, it turned into something resembling marble more than sandstone.”

The results of the research have excited many people who can see that such “biocement technology” will be a great boon to construction and mining industries—not just to someone wanting “to take their sandcastle home from the beach in the form of a solid rock sculpture”.

A Dutch company sent sand samples from Holland to Murdoch University for testing. Dr Cord-Ruwisch explained that the Netherlands has a keen interest in solidifying the dikes that prevent the sea from flooding that country’s vast areas of reclaimed low-lying land.

“Dikes would normally be made of rocks, solid stuff, but Holland is a bit like Perth in that they only have sand,” he said. “While dikes made from sand are long lasting, there are certain risks if water intrudes into the dike sand and lubricates the sand particles so they start shifting against each other. Then you can have some instability of the dikes.”¹ The Dutch have been impressed by the capability of the bacteria to cement the sand samples—hard.³

Another potential application will be in the restoration of historical buildings. As Vicky Whiffin, whose PhD thesis investigated the ability of bacteria to convert sand into stone, explained, “Cement is currently used for a lot of restoration work, but water can build up behind it and cause it to crumble away. This new biological system allows the water to leach out, which makes it a more secure option than concrete for mending heritage structures.”³

However, probably the major practical application for the biocementation technique will be in mining. “It doesn’t need oxygenation,” Cord-Ruwisch explained. “In theory we could solidify the sea bed before drilling for oil. We could also drill tunnels in the sand, we could make the sand harder so it doesn’t cave in.”¹

The take-home message from all this? In the global Flood of Noah’s day (about 4,500 years ago), there would have been lots of microbes “floating around” and buried in sand in low-oxygen conditions, just right for them to release cementing agents into the surrounding sediment. Little wonder then we see as a legacy of that watery event, lots of beautifully preserved creatures (fossils) in layers upon layers of rock-hard sediment!