The oldest oceanic crust on Earth lies at the bottom of the eastern Mediterranean in the Herodotus Basin, a seafloor depression north of Egypt and Libya.

Roi Granot, a senior lecturer and geologist at Ben-Gurion University of the Negev, discovered the ancient crust while analyzing the magnetic signatures of the Herodotus and Levant basins.

Within the Herodotus Basin, Granot identified a section of crust with magnetic stripes, the signature of crust formed on a mid-ocean ridge. The stripes are formed by magnetized minerals, which align with the Earth's magnetic field as magma cools and becomes rock.

"Here I am in the middle of the eastern Mediterranean and I see this beautiful feature that crosses the entire sea, from north to south," Granot told New Scientist. "That feature can only be created by oceanic crust."

Subduction zones on the ocean floor are highly active, constantly subsuming and recycling oceanic crust. Very little of the ocean floor is older than 200 million years old. The striped pattern suggests an anomaly -- a portion that's avoided subduction and could be up to 340 million years old, Granot says.

"Changes in the magnetic field's orientation over time are recorded in the ocean floors, creating a unique barcode that provides a time stamp for crust formation," Granot explained in a news release. "The results shed new light on the tectonic architecture and evolution of this region and have important implications on various geodynamic processes."

Previously, scientists were in disagreement on the nature and origins of the crust at the bottom of the Mediterranean -- whether it was oceanic or continental in nature.

"With the new geophysical data, we could make a big step forward in our geological understanding of the area," Granot said.

Granot published his findings this week in the journal Nature Geoscience.

Granot believes the ancient crust may be left over from the Tethys Ocean -- an ancient body of water sandwiched by the supercontinents of Gondwana and Laurasia during the Mesozoic era.