Relative and absolute dating

Relative dating
tells us the
sequence in which
events occurred,
not how long ago
they occurred.
Chronological order
- relational

a. Law of Superposition
The law of superposition states that in an
undeformed, undisturbed sequence of
sedimentary rocks, each bed is older
than the one above it and younger than
the one below it.

A Record of Uplift, Erosion,
and Deposition

b. Original Horizontality
The principle of original horizontality
means that layers of sediment are
generally deposited in a horizontal position.
Draw it
out!

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

d. Geological Column
Geologic column is an ideal sequence
of rock layers that contains all the
known fossils and rock formations on
Earth arranged from oldest to
youngest.

Absolute Dating –
• the process of
establishing the age
of an object by
determining the
number of years it
has existed.
• It’s the most precise.
It gives an actual
number to the age

A. Radioactivity
 Radioactivity - the
spontaneous decay
of certain unstable
atomic nuclei

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
(daughter).

 Radiocarbon dating is the method for
determining age by comparing the amount
of carbon-14 to the amount of carbon-12 in
a sample.
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.
B. Carbon-14

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

Relative and absolute dating

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Relative and absolute dating