The scientific investigation of the Earth’s origin began with the Danish clergyman, Nicolas Steno in 1669. Steno had been trained in anatomy and had studied fossils in rock formations.
He came up with three principles:
1. Rock layers form when particles settle at the bottom of water and are then compressed. Lower layers must be older than higher layers.
2. Rock layers are always formed horizontally. If a layer is slanted or even if it’s vertical, it was pushed into that position by later upheavals.
3. If two layers of rock are close but separate and have the same minerals, soil content and fossils, they are part of the same layer that was disrupted.
In the mid 1700s, modern geology began to take form. Two very different theories were proposed to explain the Earth’s present form. We can start with William Hutton of Scotland, born in 1736, a son of a wealthy land owner. He studied a variety of fields, got a medical degree but then decided not to be a doctor. For Hutton had a guaranteed income to pursue his main interest — the formation of the Earth.
He had a broad background in science, ideal for a new science that had no departments at universities. At the age of 50, Hutton published a pamphlet on coal. Hutton at age 57 was ready to present his theory on the Earth. He proposed that the dry land we see now had at one time had been immersed, risen again, perhaps multiple times. These changes must have taken place over a very long time.
In his book’s final chapter, Hutton concluded, “We see no vestige (sign) of a beginning, no prospect of an end.” The final version was published in 1795 and Hutton died two years later.
The French naturalist Georges Curvier came to an opposing view of the Earth through a study of fossils. Curvier concluded that many species had gone extinct. He lived in France at the time of the French Revolution. So it was natural for him to propose that the Earth had been wracked by a number of catastrophes.
Charles Lyell, another Scot, was born the same year that Hutton died. He went to Oxford, attending the geology lectures given by William Buckland, a vigorous supporter of catastrophism. Lyell visited Paris on a field trip to see Curvier’s fossils. But Lyell began to doubt that the Earth’s features were due to upheavals. At Oxford, Lyell studied the science fields of chemistry, mineralogy, zoology and botany to better understand the Earth’s past. In Lyell’s guide to geology, the guiding principle was uniformitarianism.
This means that processes now operating had been in place for very long times to bring the Earth to its present form. Lyell’s arguments were so clearly expressed that Curvier’s ideas were abandoned.
A big question remained — when was the Earth formed? In 1897, radioactivity was discovered. Radioactive atoms are unstable and decay at a different rate for each element. By measuring the proportion of radioactive elements in rocks and their decay products, one could determine the age of a rock, often going back billions of years. The moon’s oldest rocks are 4.4 billion years old; the moon was formed from debris with a smaller planet that collided with the Earth.
Alfred Wegener, a German astronomer, proposed that the continents had drifted apart over vast time spans. But there was no mechanism to explain how such huge land masses would have moved. Sonar, developed to detect submarines during World War II was used to map the ocean floors. A huge set of oceanic mountains were discovered that extended around the world.
When magnetic readings were made of the ocean floor, it was found that the Atlantic Ocean was spreading at a rate consistent with Wegener’s claims of a few inches per year for millions of years. This is called plate tectonics, the slow sliding of huge plates over the Earth’s upper mantle.
Sky sights ahead
Just before midnight on Sunday, summer officially begins. The sun’s vertical rays are farthest north at latitude 23.5 degrees north. The sun rises farthest to the north of east and sets farthest to the north of west. Daylight lasts 14 hours and 59 minutes.
The brilliant planet Venus sets about 10:20 p.m. The dim planet Mars sets just before 11 p.m. The bright planet Jupiter rises in the Southeast a little after midnight while Saturn can be seen about 11:15 p.m.
Bob Doyle is a retired science teacher at Frostburg State University who is available to talk to adult and student groups about matters related to his columns. Contact him at email@example.com.