Geology Reference
In-Depth Information
While neither of these theories accurately explains how all rocks are formed,
each contains partial truths. Some rocks do precipitate from ocean water, and
some rocks do form from volcanoes, as you discover in Chapter 7.
Developing Modern Geologic Understand-
ing
In this section, I introduce three of the most prominent geologists of the seventeenth
and eighteenth centuries and describe the theories they proposed: theories that stand
up to current scientific scrutiny and form the basis for modern geologic thought.
Reading the rock layers: Steno's stratigraphy
In the mid-seventeenth century, Nicholas Steno, a Danish physician, made great contri-
butions to geology and especially
paleontology:
the study of fossil life. When Steno
began his observations, only a few other scientists had proposed, tested, and attempted
to prove that fossils found in rocks were the remains of once-living organisms. Steno ad-
vanced these ideas through observations and the study of rocks. His work led him to
other questions, such as how could any solid object (a rock, mineral, or fossil) become
trapped within another solid object, such as a rock?
Steno is considered the father of modern
stratigraphy,
which is the study of
layers of rock. He described four principles of stratigraphy that still hold true
today:
Principle of superposition:
States that in an uninterrupted sequence of
sediment-
ary
rocks (those composed of pieces of other rocks; see Chapter 7), the rock lay-
ers below are older than the rock layers above (as long as they have not been
de-
formed,
which I describe in Chapter 9).In Figure 3-1, the principle of superposition
indicates that layer A is older than layer B, C, or E.
