Geology Reference
In-Depth Information
From the human perspective these natural processes
often act so slowly that change may not be visible
over an entire lifetime. Conversely, humans as agents
of geologic change have had an enormous impact on
the Earth's surface, an impact that is greatly out of
proportion to the amount of time humans have occu-
pied the Earth.
A necessary outgrowth of years of geologic studies
has been the development of a calendar of geologic time,
known as the geologic time scale. In the early days of
collection of fossil and rock specimens or the timing of
geologic events, a standard chronologic sequence of rel-
ative time was developed based on the way strata occur
one on top of another and on stages of evolutionary
progress shown by fossil organisms. In the last half cen-
tury radiometric dating methods have been developed
that allow precise determination of absolute time in
terms of actual years before the present (Appendix II).
Global environmental changes in the last 50,000
years have been particularly rapid and significant for the
human colony; however, the standard geologic time
scale does not adequately represent most recent time.
The Geoenvironmental Time Scale (McKenzie et al.,
1996) encompasses the standard time scale but empha-
sizes, with greater detail, recent time and includes his-
torical events (Figure 1.2). It is designed to place
environmental events in a geologic perspective. Use it
and the more detailed traditional time scale showing
eras, periods and epochs from Appendix II for answer-
ing the questions below.
QUESTIONS 1, PART C
1.
Which subdivision of geologic time represents the great-
est length of time (era, period, epoch)?
2.
What is the length in millions of years of the:
Cenozoic Era?
Tertiary Period?
Quaternary Period?
Eocene Epoch?
Pleistocene Epoch?
3. How does the Pleistocene Epoch compare in length to the
Ordovician Period?
4. Approximately how many times longer is Precambrian
time than the Cenozoic Era?
5.
What is the age in million years (Ma) of the boundary
between the Cretaceous and the Tertiary (K/T boundary)?
6.
Approximately how many years ago did the following
geologic events occur?
Mt. St. Helens eruption
New Madrid, Mo., earthquake
Vesuvius eruption
Toba eruption
