The Pentagon and other well-known buildings all over the world were built using materials made from microbes that lived about 200 million years ago, during the Jurassic Period when dinosaurs still walked on Earth.
Iconic Buildings Built Using Jurassic-Era Materials
Pentagon is built using oolitic limestone, a popular building material named for its layers of millimeter-sized spheres of carbonates called ooids.
Oolitic limestone formed all over the world throughout geologic history. It has been used as a building material since ancient times. These stones form excellent building materials because they are lightweight and strong.
Besides the Pentagon, other notable buildings that used oolites include the Buckingham Palace, the Empire State Building, 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," said Bob Burne from The Australian National University (ANU) Research School of Earth Sciences. "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."
Now, a new study conducted by Burne and colleagues offers new insights on how these ancient building materials formed.
How Ooids Form
Scientists previously believed that ooids were formed as the grains rolled on the seafloor and 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 explains on its website.
Burne and colleagues, however, found evidence suggesting that the ooids were made of concentric layers of mineralized microbes.
The researchers used an approach inspired by a mathematical model originally designed to study the growth of brain tumors and found evidence debunking the popular "snowball theory" of an ooid formation. The theory posits that small items were rolled back and forth by wind and waves in shallow tropical seas and accumulated material to form spherical shapes.
"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.
The study was published in the journal Scientific Report.
