Geology, we now know, is not static. But this is not intrinsically obvious, and so far as logic is concerned, need not be the case. It is only in relatively recent history that the constancy of geological change has been believable based on the best available scientific evidence. The ramifications of belief in geological dynamism are still reverberating.
Aristotle is often credited with inventing the scientific method, in which careful observation leads to testable hypothesis, and these tests reveal how the world works. While Aristotle oftentimes failed to test his hypotheses (for example, that eels spontaneously generate out of mud) he nevertheless was a careful observer of nature, and he recorded examples of geological change due to volcanoes and rivers, asserting that change is constant and must produce emphatic results over the course of time.
More than two millennia later James Hutton, a Scottish naturalist, published Theory of the Earth, in which he had finally accumulated and presented evidence that geological change over time occurs. Though his theory of geological change was up against the competing theories of the day, it proved to be inspirational for Charles Lyell.
Sir Charles Lyell graduated from Oxford in 1819, and went into both law and geology, though the latter interested him to a much greater degree, and he eventually took up geology full time, traveling and making careful geographic observations. In 1828 his visit to the Bay of Naples, and Mount Vesuvius, fully convinced him of the truth of geological change. On the subject of an old coastal temple, the Temple of Jupiter Serapis, Lyell writes “This celebrated monument of antiquity affords, in itself alone, unequivocal evidence that the relative level of land and sea has changed twice . . . since the Christian era.”
On the subject of Vesuvius, Lyell made as many measurements of the volcano as he could, though he notes that “I was prevented from descending into the crater by constant ejections then thrown out.” Despite this setback, he nevertheless characterizes evidence of change over time, drawing from both historic accounts of prior eruptions (such as Pliny the Younger’s account during the destruction of Pompeii), and observations of “modern” changes at the volcano.
Lyell published his careful, thoughtful observations on geological change in Principles of geology, which he concludes by stating
“The subserviency of our planet to the support of terrestrial as well as aquatic species, are secured by the elevating and depressing power of causes acting in the interior of the earth ; which, although so often the source of death and terror to the inhabitants of the globe—visiting, in succession, every zone . . .are, nevertheless, the agents of a conservative principle above all others essential to the stability of the system.”
Thus, not only is geology is constantly changing, but the geology of a given locale directly impacts animal species. The importance this insight by Lyell is easy to miss, yet hard to overstate. Charles Lyell befriended the up-and-coming scientist Charles Darwin, serving as both a friend and a mentor. Lyell’s evidence for a geologically old earth was a critical underpinning to the publication of Darwin’s On the Origin of Species, which was, notably, published by the prompting of Lyell. Corroborating evidence for evolution was simultaneously published by Alfred Wallace, also at Lyell’s prompting.
The observation of temple ruins and a living volcano therefore caused a revolutionary change in our way of thinking.
I was excited to visit Vesuvius, to observe the same volcano that Lyell, Pliny the Younger, and many others have observed and interpreted. It fascinates me that more than three million people live in the immediate, dangerous vicinity of the still-active volcano, dwarfing the estimated one thousand people that died at Pompeii. Still, my visit to Pompeii convinced me that these people are perfectly sane – the lush vegetation, cool breeze, running water, and views of the Mediterranean made Pompeii seem perfectly hospitable to me.
The volcano itself was a thrill to visit. After a short walk uphill from the end of the bus ride I was on the crater rim, taking in views of the lightly smoking crater and the Bay. I wondered what would have happened if Lyell had visited on a volcanically calm day such as that – would he have concluded that the mountain wasn’t as alive as he had first hypothesized? Or, instead would he have successfully descended to the crater bottom to take measurements, safe from “constant ejections”?
Principles of Geology by Charles Lyell
Earth by Richard Fortey