Oolitic limestone was used to build the Pentagon as well as other buildings around the world, such as Buckingham Palace and the Empire State Building. Scientists have discovered that oolitic limestone is actually a material which was made out of microbes that existed 200 million years ago, at the time of the Jurassic era when dinosaurs were still present on the Earth.
The Pentagon building was built with oolitic limestone, a stone which was named after its layers of millimeter-sized spheres of carbonates dubbed ooids. This material has been used ever since ancient times and has formed all over the world. Thanks to these stones, building materials of great quality can be formed, and they are mainly used as they are lightweight yet strong. Other buildings made out of oolitic limestone are The British Museum and St. Paul’s Cathedral.
“Jurassic oolite in England has been used to construct much of the City of Bath, the British Museum and St Paul’s Cathedral,” Bob Burne from The Australian National University (ANU) Research School of Earth Sciences explained in a press release. “Mississippian oolite found in Indiana in the US has been used to build parts of the Pentagon in Virginia and parts of the Empire State Building in New York City.”
A new study led by Bob Burne and his team gives more information about the ancient oolitic limestone and how it was formed.
How did oolitic limestone form?
Previously, scientists thought that the ooids formed from grains rolled on the seafloor and then accumulated layers of sediment.
“Oolitic limestone is a carbonate rock made up mostly of ooliths (or ooids) which are sand-sized carbonate particles that have concentric rings of CaCO3. These rings are formed around grains of sand or shell fragments that were rolled around on the shallow sea floor, gathering layer after layer of limestone,” University College London gave an explanation on its website.
Burne and his team discovered new evidence which indicates that this material was formed out of concentric layers of mineralized microbes. They were inspired by a mathematical model which was used to study the growth of brain tumors. The evidence they found debunks the “snowball” theory of ooid formation. According to the “snowball” theory, small grains were rolled back and forth by wind and waves in shallow tropical seas and formed spherical shapes with accumulating material.
“The structure of the typical ooid does not reflect successive surface accretion of carbonate mud on the surface of a rolling grain, as suggested by Sorby, but rather provides a detailed archive of organo-sedimentary concentric accumulation,” the researchers wrote in their study which was published in Scientific Reports.