A geological fault system forming off the coast of Portugal signals the beginning of the end for an ocean: the Atlantic will shrink and eventually disappear as Europe approaches the Americas, a new study suggests. The same thing happened to another ancient ocean, which shrank and is now called the Mediterranean.
According to research published in the journal Geology, the death of the Atlantic is foreshadowed by faults identified off the Iberian Peninsula, as well as by two powerful but mysterious earthquakes that struck Portugal in 1775 and 1969.
It has been known for decades that Earth's continents are not fixed formations. Instead, they follow the so-called Wilson Cycle, in which land masses first move apart and then reunite to form supercontinents like Pangaea. And this formation and subsequent breakup of supercontinents has occurred at least three times in the last four billion years.
When continents move apart, deep cracks called mid-ocean ridges form between them, from which magma gushes out, thus closing the gap. Conversely, when continents approach each other, a subduction zone forms between them—a zone in which the tectonic plate of one continent slowly sinks beneath the plate of the other.
Dr João Duarte's team at Monash University in Australia examined available data for the suspected earthquakes of 1775 and 1969 and additionally mapped the crust off Portugal.
"The significant seismic activity indicates that there is convergent tectonic movement," the researcher says. "It's something like an embryonic subduction zone," he comments.
The research team also estimates that the new subduction zone is being formed due to the influence of the so-called Gibraltar Arc - a subduction zone in the western Mediterranean, which was also once an ocean, until Africa began to approach Eurasia.
"Subsidence can behave like a contagious disease," which spread from the Mediterranean to the Atlantic, Duarte says.
But even if his estimates are correct, America will not appear on Europe's horizon soon: the subduction zone is estimated to take 20 million years to fully activate, and then it will take another 220 million years until the Iberian Peninsula collides with America.
