Class Slides Set 10A
Special Skills Used to Study Early Humans
. . . or how to make sense
out of
Ch. 8 of the text . . .
Prehistoric Cultures
Tim Roufs’ section ©2009
Archaeological
Dating
Methods
In the Field and Lab
methods =
basic overall approaches to a
problem
techniques =
specific tools / procedures used
In the Field and Lab
archaeological
dating methods
1. relative dating
2. chronometric dating
(aka “absolute” dating)
Relative and Chronometric Dating
Understanding Humans,
10th
Ed., p. 189.
REM: relative
methods
tell you whether something is
older / younger / the same age
Understanding Humans, 10th Ed., p. 188.
methods
REM: chronometric
methods
yield yield a date
often scaled in calendar years
Understanding Humans, 10th Ed., p. 188.
method
technique
Relative and “Absolute” (Chronometric) Dating Techniques.
Michels, Dating Methods in Archaeology, p. 4.
techniques
technique
People of the Earth, 10th Ed., p. 11.
In the Field and Lab
stratigraphy
the sequence of geological strata, or
layers, formed by materials deposited by
water or wind
also the study of this sequence
REM: relative
methods
tell you whether something is
older / younger / the same age
Understanding Humans, 10th Ed., p. 188.
Humankind Emerging, 7th Ed., p. 24.
People of the Earth, p. 18.
Main gorge at Olduvai. Note geological beds.
Understanding Humans, 10th Ed., p. 197.
Bed I
Olduvai Gorge, Kenya.
Hoebel, Anthropology: The Study of Man and Archaeology, 4th Ed., p. 153.
In the Field and Lab
archaeological
dating methods
1. relative dating
2. chronometric dating
(aka “absolute” dating)
In the Field and Lab
archaeological dating methods
2. chronometric dating
(aka “absolute” dating)
provides estimates in
actual numbers of years
(sometimes +/-)
Relative and Chronometric Dating
Understanding Humans, 10th Ed., p. 189.
In the Field and Lab
archaeological dating methods
2. chronometric dating
(aka “absolute” dating)
determining the actual age of
geological deposits (and the fossils in
them) by examining the chemical
composition of rock fragments and
organic remains containing radioactive
substances such as uranium 238, and
carbon 14, which decay at a known rate
In the Field and Lab
A.1. or “First Order
Absolute Dating”
direct determination of age
based on internal evidence
e.g.,
14C
dating of bone sample
e.g., dendrochronology
e.g., molecular clocks
Relative and Chronometric Dating
Understanding Humans, 10th Ed., p. 189.
Technician in a radiocarbon dating laboratory.
Understanding Humans, 10th Ed., p. 194.
Radiocarbon dating:
• method was developed in the
1940’s by Willard Libby and a
team of scientists at the
University of Chicago.
Very powerful in dating artifacts
•and
geological events up to
about 50,000 years ago.
Radiocarbon dating relies on a simple natural phenomenon. As the
earth’s upper atmosphere is bombarded by cosmic radiation,
atmospheric nitrogen is broken down into an unstable isotope of
carbon– carbon 14 (C-14).
Because it reacts identically to C-12 and C-13, C-14 becomes
attached to complex organic molecules through photosynthesis in
plants and becomes part of their molecular makeup.
Animals eating those plants in turn absorb Carbon-14 as well as the
stable isotopes. This process of ingesting C-14 continues as long as the
plant or animal remains alive.
The C-14 within an organism is continually decaying into stable carbon
isotopes, but since the organism is absorbing more C-14 during its life,
the ratio of C-12 remains about the same as the ratio in the atmosphere.
When the organism dies, the ratio of C-14 within its carcass begins to
gradually decrease. The ratio of decrease is ½ the quantity at death
every 5,730 years. That is the half life of C-14.
techniques
technique
People of the Earth, 10th Ed., p. 11.