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People Behind the Science

James Hutton (1726–1797)

ames Hutton was a Scottish natural phi- intensity (the principle later known as uni-
Jlosopher who pioneered uniformitarian formitarianism). In Earth’s economy, in the
geology. The son of an Edinburgh merchant, imperceptible creation and devastation of
Hutton studied at Edinburgh Uni versity, landforms, there was no vestige of a begin-

Paris, and Leiden, training first for the law ning nor prospect of an end. Continents
but taking his doctorate in medicine in 1749 were continually being gradually eroded by
(although he never practiced). He spent the rivers and weather. Denuded debris accu-
next two decades traveling and farming in mulated on the seabed, to be consolidated
the southeast of Scotland. During this time, into strata and subsequently thrust upward
he cultivated a love of science and philoso- to form new continents thanks to the action
phy, developing a special taste for geology. of Earth’s central heat. Nonstratified rocks
About 1768, he returned to his native such as granite were of igneous origin. All
Edinburgh. A friend of Joseph Black, William Earth’s processes were exceptionally leisurely,
Cullen, and James Watt, Hutton shone as a and hence, Earth must be incalculably old.
leading member of the scientific and literary Although supported by the experi-
establishment, playing a large role in the early mental findings of Sir James Hall, Hut-
history of the Royal Society of Edinburgh and ton’s theory was vehemently attacked in its
in the Scottish Enlight enment. day, partly because it appeared to point to
Hutton wrote widely on many areas work, Hutton attempted (on the basis of an eternal Earth and hence to atheism. It
of natural science, including chemistry, both theoretical considerations and per- found greater favor when popularized by
but he is best known for his geology, set sonal fieldwork) to demonstrate that Earth Hutton’s friend John Playfair and later by
out in his Theory of the Earth, of which a formed a steady-state system in which ter- Charles Lyell. The notion of uniformitari-
short version appeared in 1788, followed restrial causes had always been of the same anism still forms the groundwork for much
by the definitive statement in 1795. In that kind as at present, acting with comparable geological reasoning.

Source: From the Hutchinson Dictionary of Scientific Biography. © Research Machines plc 2003. All Rights Reserved. Helicon Publishing is a division of Research Machines.

Juan de Fuca Plate is subducted beneath the continental litho- converging boundaries are the places of folding, faulting, and
sphere, and as it descends, it comes under higher and higher associated earthquakes. They are also the places of volcanic
temperatures. Partial melting takes place, forming magma. The activities, events that build and thicken Earth’s crust. Thus,
magma is less dense than the surrounding rock and is buoyed plate tectonics explains that mountains are built as the crust
toward Earth’s surface, erupting as a volcano. thickens at a convergent boundary between two plates. These
Overall, the origin of mountain systems and belts of mountains are slowly weathered and worn down as the next
mountains such as the Cascades involves a complex mixture belt of mountains begins to build at the new continental edge.
of volcanic activity as well as folding and faulting. An indi- How long does it take to build a mountain and then wear it
vidual mountain, such as Mount St. Helens, can be identified completely down to sea level? How would you ever find an
as having a volcanic origin. The overall picture is best seen, answer to this question? These questions will be discussed
however, from generalizations about how the mountains have in chapter 21. First, we must consider how the land is worn
grown along the edges of plates that are converging. Such down, the topic of chapter 20.

SUMMARY

The principle of uniformity is the frame of reference that the geologic Stress is a force that tends to compress, pull apart, or deform a rock,
processes you see changing rocks today are the same processes that and the adjustment to stress is called strain. Rocks respond to stress by
changed them in the past. (1) withstanding the stress without change, (2) undergoing elastic strain,
Diastrophism is the process of deformation that changes Earth’s (3) undergoing plastic strain, or (4) breaking in fracture strain. Exactly
surface, and the movement of magma is called vulcanism or volcanism. how a particular rock responds to stress depends on (1) the nature of
Diastrophism, volcanism, and earthquakes are closely related, and their the rock, (2) the temperature, and (3) how quickly the stress is applied.
occurrence can be explained most of the time by events involving plate Deeply buried rocks are at a higher temperature and tend to
tectonics. undergo plastic deformation, resulting in a wrinkling of the layers into

494 CHAPTER 19 Building Earth’s Surface 19-18