“What did people think earthquakes were in the olden days?”

Graphic from the 1955 World Book Encyclopedia explaining the latest scientific theory on what happens when there's an earthquake. (Image: 1955 World Book Encyclopedia, Vol. E, p. 2169)
Illustration from the 1955 World Book Encyclopedia explaining the latest scientific theory on what happens when there’s an earthquake. (Image: 1955 World Book Encyclopedia, Vol. E, p. 2169)

As the oldest member of my particular household, I am always relieved when The Five-Year-Old’s my-agile-brain-cannot-comprehend-your-extreme-agedness comments are directed at Daddyo instead of me.

The Five-Year-Old, curiously: “Daddyo, what are earthquakes?”

Daddyo, didactically: “The shifting of the earth’s tectonic plates.”

The Five-Year-Old, impatiently: “I know that, but what did people think they were in the olden days? Like when you were born.”

Although it is painful for me to refer to the year of Daddyo’s birth as the “olden days,” the sad fact is Daddyo’s birth predates the Intertubes. And it turns out searching for “what did scientists think caused earthquakes in 1973” is not a terribly fruitful activity. However, I can answer this question in another way.

What did Daddyo think caused earthquakes while he was growing up?

I like this approach better not because I can poke Daddyo in the shoulder and ask him (his childhood memories occasionally incorporate the latest scientific theories decades before they were developed), but because our library includes the complete set of the 1955 World Book Encyclopedia. The very Encyclopedia that Daddyo claims to have read from cover to cover while staying at his grandparents’ farm in Alabama as a boy. You may scoff at this as an unlikely accomplishment for a twelve-year-old Daddyo, but I know better.

So what does the 1955 World Book Encyclopedia say?

Flipping to page 2168 of Volume E yields this gold mine of earthquake lore:

Causes of Earthquakes. Many people have believed that volcanoes were responsible for earthquakes, because there are many volcanoes in the earthquake belts. Actually, both volcanoes and earthquakes are connected with the same set of causes. The earth often trembles because of sudden movements in the rocks below the earth’s surface. The inside of the earth is affected by many different forces. These forces push against the rocks beyond the point at which the rocks can give, or stretch. Then the rocks break along lines called faults, and an earthquake results. Sections of rock slip past each other and set up vibrations which cause the earth to tremble. Sometimes the forces below the surface of the earth thrust up sections of the earth to form mountains. Earthquakes can be caused by the forces which create mountains. When mountains begin to settle, the earth may slip and cause earthquakes.”

Well, ok. So it’s not too much different from how a layperson might explain these things to a Five-Year-Old today. The entry rather neatly skirts the topic of what is causing those tremendous forces, but then again at the time it was written that was still the topic of hot debate.

Quick! What's missing from this diagram of the Earth's core? (Image: 1955 World Book Encyclopedia, Volume E, page 2166c)
Quick! What’s missing from this diagram of the Earth’s core? (Image: 1955 World Book Encyclopedia, Volume E, page 2166c)

It’s a little surprising to think about now, considering how hard-wired plate tectonics is in our brains these days. After all, Alfred Wegener introduced his theory of continental drift (the idea that modern plate tectonics is based on) way back in 1912.

But in 1955, the main evidence for continental drift — the idea that the continents were not fixed but were drifting across the sea floor — was still mainly the uncanny way the rocks of South America’s east coast matched up with those on the west coast of Africa, and hints in the fossil record that South America, Africa, Antarctica, India and Australia shared a common set of plants and animals a very long time ago. So I suppose it isn’t too surprising that scientists would hold out for more data before accepting the idea of a free-range Australia.

Unfortunately for the 1955 World Book, the ground-breaking studies that created modern plate tectonics wouldn’t be complete until nearly a decade after its publication. In the late 1950s and early 1960s, Harry Hess of Princeton University and a rather sizable team of co-researchers published data that demonstrated that the seafloor was expanding along the mid-oceanic ridges. At the same time, advances in early seismic imaging helped scientists prove that the ocean floor was actually disappearing into the mantle along the edges of the continents, at a rate that neatly counterbalanced the seafloor’s expansion along the mid-oceanic ridges. The two discoveries (along with a host of other findings about the magnetic properties of the ocean floor and the development of marine geology in general) transformed Wegener’s theory of continental drift into today’s plate tectonics around 1965.

Oh yeah, those. Convection currents in the Earth's core. (Image: public domain. Source: U.S. government)
Oh yeah, those. Convection currents in the Earth’s mantle. (Image: public domain, based on artwork from the U.S. Geological Survey.)

Of course, that gets us to our answer, doesn’t it?

In the olden days when Daddyo was born, people thought earthquakes were caused by plate tectonics.

The Five-Year-Old, impatiently: “No, I mean what did people think caused earthquakes before that. I want you to tell me the stories.”

Mommyo: “You mean like earthquakes are caused by the gods getting angry and stuff?”

The Five-Year-Old, enthusiastically: “Yeah, that.”

Mommyo: “That, my little Caterpickle, is a post for another day.”

Specifically, Wednesday. See you then.

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