Geologic time scale 1 Geomorphology Chapter

1. • Geologic Time Scale:
• Its History and Development
Scottish geologist James Hutton (1726-1797) set the stage
for the development of the geologic time scale in the late
18th century with the publication of his Theory of the Earth
(1785). In it, Hutton advanced "uniformitarianism," a
geological doctrine which basically assumes that current
geologic processes, occurring at the same rates observed
today, in the same manner, account for all of Earth's
geological features.
• Next, British civil engineer, surveyor and amateur
geologist William Smith (1769-1839) made the discovery
that fossils are found buried in a definite order. The
geologic time scale was developed shortly thereafter.

2. • Geologic Time Scale
• The earth's crust consists of many layers of
sedimentary rock (called "strata"). Geologists
assume that each layer represents a long period
of time, typically millions of years. This is
actually a secondary assumption based upon
the primary assumption of Uniformitarianism.
These layers of sedimentary rock contain billions
of fossil remains and some of these fossils are
unique to certain layers. The layers are
catalogued and arbitrarily arranged into a
specific order (not necessarily the order in which
they are found). This order reflects the
assumption of macro-evolution (the widely held
notion that all life is related and has descended
from a common ancestor).

3. • Geologic Time Scale: Circular Reasoning
• We determine the age of the rock by the assumed age of the
index fossils it contains, then, to determine the age of all the
other fossils in the same layer of rock. The succession of
organisms has been determined by a study of their remains
embedded in the rocks, and the relative ages of the rocks are
determined by the remains of organisms that they contain." (R.
H. Rastall, "Geology", Encyclopedia Britannica, vol. 10, 1954,
p. 168)
• The geologic time scale provides a system of chronologic
measurement relating stratigraphy to time that is used by
geologists, paleontologists and other earth scientists to
describe the timing and relationships between events that
have occurred during the history of the Earth.
• It is a period of time covering the physical formation and
development of Earth, especially the period prior to human
history.
• Evidence from radiometric dating indicates that the Earth is
about 4.570 billion years old.

4. • Stratigraphy refers
to geological and
archaeological
layers that make
up an
archaeological
deposit.

5. William Smith's monograph on identifying strata based on fossils
(The remains of a once-living organism is called fossil)

6. Aegicerus sp
Heritiera sp Aegicerus
comiculatum
Xylicarpus sp Phoenix paludosa
Lumnitzera
racemosa

10. • ice age
Any geologic period during which thick ice sheets cover vast areas of land.
Such periods of large-scale glaciation may last several million years and
drastically reshape surface features of entire continents. A number of
major ice ages have occurred throughout the Earth's history; the most
recent periods were during the Pleistocene Epoch (1.8 million–10,000
years ago).