To read more from Daniel, visit his blog: Sic Et Non.
On the morning of Saturday, 1 November 1755, the churches of Lisbon, in Portugal, were packed with worshipers. It was the feast of “All Saints Day.” Every candle was lit. Every church was filled with flowers and other flammable decorations. The first tremor hit partway through church services, at a magnitude that has been estimated as high as 8.5 or even 9.0. It lasted for about 3.5 minutes.
Much of the city was reduced to rubble and almost instantly in flames, so people rushed for the safety of the harbor and the open docks. Amazingly, the water drained from the Rio Tejo estuary, revealing shipwrecks still laden with lost cargo. Thousands of people rushed into the muddy riverbed, scavenging for treasure.
Forty-five minutes after the first quake, the first of three tsunamis hit the city. It came on so fast that people on horseback were forced to gallop to higher ground in terror for their lives. The final death toll may have come to 75,000. (Lisbon’s population at the time of the disaster was probably about 250,000 altogether.)
The impact of the “Great Lisbon Quake” was enormous, not only physically but both culturally and politically. One person who was deeply influenced by it was the great French writer commonly known as Voltaire. His famous 1759 book “Candide, ou l’Optimisme”—generally known in English simply as “Candide”—deals with the problem of reconciling the existence of God with evil and human suffering. Deeply cynical but wonderfully witty, “Candide” was inspired by the Lisbon quake and even includes the quake in its storyline. It also features among its major characters “Professor Pangloss,” who continually insists, despite the horrors around him, that “all is for the best” in this, the “best of all possible worlds.”
Many other seismic disasters preceded the Great Lisbon Quake, and many others have followed it. They continue to raise the acute question of “theodicy”—how to defend ideas of Providence and divine goodness in the face of massive evil. It is one of the most serious challenges facing believers in God.
Early on the morning of Monday, 6 February 2023, a massive earthquake—estimated at magnitude 7.8, the equivalent of detonating eight million tons of TNT—struck southern and central Türkiye (the proper name for what we English-speakers have long called “Turkey”), with lethal effects extending into northern and western Syria. Scores of aftershocks followed, including, just a few hours later, a 7.5 magnitude event that would have counted as a significant earthquake in and of itself, and two weeks later, a magnitude 6.4 shock. As I write, the death toll from the temblors is approaching 50,000. And the terrible suffering has been made even worse by political dysfunction and severe winter cold.
So what caused the 6 November Turkish quake and its aftershocks? A bit of background is in order:
One of the best-established ideas in modern geology is that of “plate tectonics.” It grew out of the proposal by the German scientist Alfred Wegener of what he termed “die Verschiebung der Kontinente” or, in English, “continental drift.” Unfortunately for Wegener, his theory was rejected by most of his contemporaries. It gained general acceptance only after his death at the age of fifty during a 1930 expedition to Greenland.
According to the plate tectonic model, the rocky surface or crust of our planet is composed of large “plates” that have been slowly moving, floating above Earth’s mantle, for roughly the past 3.4 billion years. When two of these plates collide head-on, one of them tends to dive down into the mantle below the other in a process known as “subduction.” Typically, oceanic crust subducts below continental crust.
Most of modern-day Türkiye rides atop a portion of Earth’s crust known as the Anatolian Plate, the edge of which is very near the Turkish border with Syria. It isn’t the only tectonic plate in the eastern Mediterranean basin, which, geologically speaking, resembles a giant jigsaw puzzle. All of these plates are in slow but constant motion. In particular, the massive Arabian Plate, which abuts the Anatolian Plate to the south, is pushing northward. What happened in early February originated along the East Anatolian Fault Zone, which runs between the Anatolian Plate to the north and the Arabian Plate to the south. It seems that the pressure of the colliding plates became too high for the crust to sustain. The Anatolian Plate gave way, lurching suddenly to the west.
Earthquakes are plainly bad things from a human perspective. Seismic pressures like those that resulted in the Great Lisbon Earthquake and the 2023 Gaziantep Earthquake commonly build up over centuries—small change, a blip, in geological terms. But they can fundamentally alter human lives and annihilate human treasures in mere seconds.
Still, many scientists have held that plate tectonics, which causes them, may be necessary for life on our planet.
No other planet in our solar system has plate tectonics, which seems to be unique to Earth. Other planets—exoplanets—revolving around other stars may possess similar geology but, if so, we haven’t found them.
But why might plate tectonics, and specifically subduction, be vital for life on Earth? Because the process of subduction helps to maintain an available supply of the roughly twenty chemical elements that life requires.
Organisms in the oceans consume elements that are essential to life, including carbon, phosphorus, nitrogen, and sulfur. Then they die, sinking to the bottom of the oceans until they are eventually buried in sediment that is, in many places, many thousands of feet thick. (Mostly chalk and limestone, it has been accumulating for millions of years, and it continues to accumulate.). As time passes, they are separated from the biosphere, the areas on land and in the sea where life exists, and they are thus rendered unavailable for later generations of living organisms.
On land, continual erosion wears down mountains and soil, washing them eventually into the ocean. Over time, if that were the end of the story, the elements necessary for life would all have been removed into the sea. Without carbon, for instance, there can be no carbon-based life, whether on earth or in the seas. And carbon-based life is the only kind of life we know. (In the natural world, current science suggests that carbon may be the only realistic basis for organic life. Silicon-based life forms, long popular in science fiction, may not actually be possible.) Given continual erosion over hundreds of millions and even billions of years, Earth’s land areas would be exhausted and lifeless. Earth’s mountains would all have been ground down into sterile plains.
But at least vital nutrients in the oceans would be continually replaced. Right? No. Run-off from the earth’s land masses, via erosion and rivers, would not be enough to perpetually replenish the elements lost through death and sedimentation in the sea. Eventually, the land areas of Earth would be without the needed elements. The replenishment of the oceans would stop.
So why aren’t the oceans sterile? The answer seems to lie in subduction. Ocean sediments are dragged down deep into the earth on the surface of subducting oceanic slabs. When those slabs go deep enough, they melt, beginning with the sediments riding atop them. Water trapped in the subducting plates is also released into the mantle, which enhances the mantle’s melting, which in turn fosters the development of volcanos on the continental or oceanic plate above. Eventually, those elements—including carbon and sulfur—move back up to the surface of the earth through plumes of magma. Then, through volcanic eruptions, they are released back up onto the earth’s surface and into its atmosphere.
Through plate tectonics and the recycling that results from subduction, the continental and oceanic crusts, Earth’s rocky outer layer, are continually being formed and reformed. Erosion from the mountains can continue to fertilize the oceans, accompanied by underwater volcanos such as Hunga Tonga–Hunga Ha‘apai, near Tonga, which erupted spectacularly in early 2022. Hunga Tonga—Hunga Ha’apai is part of the Kermadec-Tonga subduction zone, which is formed by the subduction of the Pacific Plate under the Indo-Australian Plate. Another place where such replenishment occurs is at mid-ocean ridges, which occur where oceanic plates are diverging. As the plates separate, molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt and, thus, creating new ocean floor.
Ordinary tourists can also view very visible illustrations of the creation of new land on and near the Big Island of Hawaii. The Hawaiian Islands are very far from any plate boundary, but they are riding on the Pacific Plate, which is moving to the northwest at a speed of roughly three to four inches a year. It is moving over a stationary hot spot—a place of exceptional heat originating at the boundary between Earth’s core and its mantle—where magma has seared through the oceanic crust. In order from oldest to youngest, the resulting volcanos have created Kauai, Oahu, Molokai, Maui, and the Big Island (which is still under construction). A new island is arising offshore to the south, beneath the surface of the sea.
So subduction causes destruction, but it also recycles elements that are essential to life from the biosphere to the geosphere and back into the biosphere. It is not clear that, without plate tectonics, Earth would have atmospheric oxygen or, for that matter, any kind of complex life.
Thus, despite the continual erosion of the continental crust and the constant and seemingly irretrievable depositing of oceanic minerals into deepening sediments on the seabed, a relatively consistent supply of vitally important elements has been preserved on land and in the sea over enormous eras of time, permitting life. Permitting us.
Can we join Professor Pangloss in declaring, therefore, that “all is for the best” in this, the “best of all possible worlds”? I think that we need to be humble before great mysteries. Neither our scientific understanding nor our understanding of the mind of God is adequate to speak confidently about such things. But it may in fact be the case that plate tectonics, for all the pain and suffering that result from the stresses and strains of subduction, offers the best of all actually possible fallen worlds for mortal human probation.
In the meantime, such catastrophes as the recent Turkish earthquake test us in more immediate and obvious ways: How will we respond? The prime minister of Portugal at the time of the 1755 earthquake, who is generally known as the Marquis of Pombal, drew wide respect for his competent and compassionate response to that disaster, and he continues to be revered still today. At one point, soon after the virtual destruction of Lisbon, he was asked what should be done. His simple reply? “Bury the dead and heal the living.”