. . . or how to make sense

out of

Ch. 8 of the text . . .

Prehistoric Cultures

Tim Roufs’ section ©2009

Class Slides Set 10A

Special Skills Used to Study Early Humans

ArchaeologicalArchaeological

DatingDating

MethodsMethods

In the Field and LabIn the Field and Lab

techniques =

specific tools / procedures used

methods =basic overall approaches to a

problem

In the Field and LabIn the Field and Lab

archaeological dating methods

1. relative dating2. chronometric dating

(aka “absolute” dating)

Relative and Chronometric DatingUnderstanding Humans, 10th Ed., p. 189.

Understanding Humans, 10th Ed., p. 188.

REM: relative

methods

tell you whether something is

older / younger / the same age

methods

Understanding Humans, 10th Ed., p. 188.

REM: chronometric

methods

yield yield a date

often scaled in calendar years

Michels, Dating Methods in Archaeology, p. 4.

Relative and “Absolute” (Chronometric) Dating Techniques.

method technique

People of the Earth, 10th Ed., p. 11.

technique

techniques

In the Field and LabIn 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

Understanding Humans, 10th Ed., p. 188.

REM: relative

methods

tell you whether something is

older / younger / the same age

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.

Hoebel, Anthropology: The Study of Man and Archaeology, 4th Ed., p. 153.

Olduvai Gorge, Kenya.

Bed I

In the Field and LabIn the Field and Lab

archaeological dating methods

1. relative dating2. chronometric dating

(aka “absolute” dating)

In the Field and LabIn 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 LabIn the Field and Lab

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

archaeological dating methods

In the Field and LabIn 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 samplee.g., dendrochronologye.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.

People of the Earth, 10th Ed., p. 11.

technique

techniques