Age of the Earth, Illustrated: Almost A Century Ago

The Lemming thought that a chart that went with this article looked a little cool. Also, for me, nostalgic. I remember seeing illustrations like that in my school textbooks.

If the science presented here seems a little - dated? - you've been paying attention. The bibliography at the end of RLM's piece is mostly from the second and third decades of the 20th century. We've learned a little more since then.

"The Geological Succession of Life in Kentucky"
Roy Lee Moodie, University of Kentucky

"The origin of the earth, from the viewpoint of geology and astronomy, is best accounted for by the Planetesimal Hypothesis, which is to the effect that, the earth, instead of originally being a molten mass, grew to its present form by the accretion of cold bodies from outer space. When the earth had attained about two-thirds its present size it is held that there was enough attractive force to retain a warm blanket of atmosphere. The presence of living things then became possible; simple plants and animals may then have begun to live.

"AGE OF THE EARTH

"The age of the earth is usually expressed in terms of millions of years, but such statements are largely meaningless since none of us can comprehend the vast stretches of time indicated by even a million years. It will help somewhat to understand the meanings of geological time if we say that the Mammoth Cave, in Edmonson County, had been in existence for many thousands of years when the most ancient Egyptians were first entering the Nile Valley, long before any of the pyramids had been thought of, thousands of years before the city of Babylon was built. Huge mountain chains had arisen and were worn down long before the waters of the earth had dissolved the first tiny crevice of the colossal cavern. When we realize that solid rock blocks creep down a slope at the rate of about one inch a century, or that a thousand years may bring about almost imperceptible changes in earth's feature, then we gain some concept of the meaning of geological time.

"DIVISIONS OF GEOLOGICAL TIME
"DIAGRAMMATIC SECTION OF EARTH'S CRUST


(From UKY, used w/o permission)
"Fig. 2. Kentucky geological history occupies only the middle part of the geological column shown here...."

I'll repeat that last bit: "...Kentucky geological history occupies only the middle part of the geological column shown here...." Since there are seven divisions of time in the chart, the middle part would be the Paleozoic. Which, again according to the chart, would be under a maximum thickness of 98,000 feet of rock.

That's about 18½ miles.

I'd make a crack about the paper assuming that the surface of Kentucky was over a dozen miles below sea level - but let's get real. The chart says maximum thickness.

Given what was known at the time, the ideas presented in that paper weren't particularly crazy. But scientists of that era kept collecting and analyzing data, which is what they're supposed to do. There are reasons why geologists eventually gave up on the Planetesimal Hypothesis. Which is another topic.

This page, by the way, is part of an online publication of a 1931 symposium.

The Kentucky Paleontological Society, on the same site, a directory or two up, or over, or down - depending on your frame of reference - is more up-to-date.Related posts, at

• "Change, American Culture, Trilobites, Humanity's History, and the Big Picture"