However, since the technique involves moving spheroids one at a time, it could take days to build a one cubic centimeter structure.

GSNR’s project would raise pollution levels by roughly 1 microgram per cubic meter for the duration of its operations in the port area.

For particulate matter, the team measured peak concentrations in micrograms per cubic metre of air.

Until now, the process by which a million cubic kilometres of salt accumulated in the Mediterranean basin over such a short period of time remained unknown.

Once the gravel is in place, the builders will add about 6,000 cubic yards of “engineered soil” to the structure, Rock said.