Geology Reference
In-Depth Information
Water:
The most common surface processes include the movement of rocks and
sediment by flowing water in river and stream channels. The water makes its way
across earth' surface by removing and depositing sediment, reshaping the land-
scape as it does. The different ways flowing water shapes the land are described in
Chapter 12.
Ice:
Similar to flowing water but much more powerful, ice moves rocks and can
shape the landscape of an entire continent through glacier movements. The slow-
flowing movement of ice and its effect on the landscape are described in Chapter
13.
Wind:
The force of wind is most common in dry regions, and you are probably fa-
miliar with the landforms it creates, called
dunes.
You may not realize that the
speed and direction of wind create many different types of dunes, which I describe
in Chapter 14.
Waves:
Along the coast, water in the form of waves is responsible for shaping
shorelines and creating (or destroying) beaches. In Chapter 15, I describe in detail
the various coastal landforms created as waves remove or leave behind sedi-
ments.
Interpreting a Long History of Life on
Earth
One of the advantages of studying geology is being able to learn what mysteries of the
past are hidden in the rocks. Sedimentary rocks, formed layer by layer over long periods
of time, tell the story of earth's history: changing climates and environments, as well as
the evolution of life from single cells to modern complexity.
Using relative versus absolute dating
Scientists use two approaches to determine the age of rocks and rock layers: relative
dating and absolute dating.
Relative dating
provides ages of rock layers in relation to one another — for example,
stating that one layer is older or younger than another is. The study of rock layers, or
strata,
is called
stratigraphy.
In methods of relative dating, geologists apply
principles of
stratigraphy
such as these:
