b. Original Horizontality
The principle of original horizontality
means that layers of sediment are
generally deposited in a horizontal position.
c. Index fossils
• Index fossils are used to determine
approximate age. Index fossils are
widespread geographically, are
limited to a short span of geologic
time, and occur in large numbers.
FOUND IN SEDIMENTARY ROCKS
Absolute Dating –
• the process of
establishing the age
of an object by
number of years it
• It’s the most precise.
It gives an actual
number to the age
Radioactivity - the
of certain unstable
1. Half - life
A half-life is the amount of time necessary
for one-half of the nuclei in a sample
(parent) to decay to a stable isotope
Radiocarbon dating is the method for
determining age by comparing the amount
of carbon-14 to the amount of carbon-12 in
1. When an organism dies, the amount of
carbon-14 it contains gradually decreases
as it decays.
2. By comparing the ratio of carbon14 to
carbon-12 in a sample, radiocarbon dates
can be determined.
Radioactive atom has an
unstable nucleus that decays
a. Radiation is given off
b. Decay is at a constant rate
c. Decay material is formed
d. Half-life is the amount of
time for ½ of the
radioactive element to decay
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