Timestone 15
40,000 to 10,000 years ago
modern Homo sapiens-Cro-Magnon
This specimen shows a fully modern Homo sapiens from Europe.
The most amazing feature of Cro-Magnon was not physical, but cultural-art,
body ornaments, and signs of astronomy and math.
The term "Cro-Magnon" describes both a specific skull and
a cultural time period. During this time throughout the world, humans
showed a burst of cultural activity with artistic objects, jewelry
(made from bones, teeth, shell, and ivory), musical instruments (made
from bones), and beautiful cave art.
Cast of fossil "Old Man of Cro-Magnon" skull
Homo sapiens
Found in Cro-Magnon rock shelter, Les Eyzies, Dordogne, France, in
1868 by workers building a railway
Age: 30,000 years
Cro-Magnon Cave
Ice-age artists
Within the chambers of Chauvet Cave are some
of the world's oldest known paintings. The artworkshows hundreds of
animals and more than a dozen species. There are images of horses,
rhinoceroses, bison, mammoths, cave lions, and cave bears. The artists
painted and drew with red ochre and charcoal or scratched into the
soft walls. The elegant art showed they had mastered the advanced
techniques of shading and perspective.
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"Cro-Magnon"
Reconstruction
Artist: William Munns
This fully modern human lived in what is now Europe. Homo
sapiens evolved in a warm environment. Scientists believe
that Cro-Magnon migrated from a warmer climate in what is
now Africa through the Middle East to the colder climate of
Europe.
Fossil
Dating
Relative or absolute age
To find the age of a hominid fossil, there are two types of
techniques: relative and absolute. Relative dating identifies
a fossil as older or younger than surrounding material. Absolute
dating identifies the actual age of a fossil or the surrounding
material. All dating techniques have drawbacks, so researchers
often use several techniques to date a fossil.
Relative Dating Techniques
Stratigraphy
As soil and rock layers build up over time, deeper layers
are usually older than shallower layers. From this scientists
infer that a fossil is older than the layer above it and younger
than the layer below it. If scientists know the ages of the
rock or soil layers, they can estimate the age range of the
fossil.
Biostratigraphy
Scientists know a lot about how animal groups have changed
over time, so they use animal fossils to mark specific time
periods. The fossils of pigs, elephants, and horses are especially
useful. If scientists find a hominid fossil, they can determine
its age relative to a fossil pig, for example, found in the
same rock layer nearby or at another site.
Paleomagnetism
Earth's magnetic field changes direction and intensity from
time to time. Today the magnetic pole is north, but is has
been south in the past. As rocks form from cooling volcanic
material, some minerals retain the direction of the magnetic
pole. Scientists have charted the age of rocks based on the
magnetic records they contain. They can use this magnetic
clock to determine the relative age of fossils in rocks as
old as 5 million years.
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Palynology (pollen analysis)
When plants shed pollen, it collects in the soil and layers
build up. For many sites scientists have determined the dates
for each pollen layer. By looking closely at the pollen at a
site, scientists can determine the past climate and environment
of a hominid fossil found in the same layer. Pollen analysis
can also show how local plant communities change over time.
Carbon-14 or radiocarbon dating
When an organism is alive, it contains a ratio of carbon-12
and the isotope carbon-14 that is the same as the ratio in the
atmosphere. When the organism dies, C-14 decays and the ratio
between C-12 and C-14 changes. Scientists measure this change
to determine when the organism died. This technique works on
organic material, such as wood or bone, younger than 50,000
years.
Electron spin resonance dating
This dating technique measures the electrons of the mineral
hydroxyapatite trapped in the crystal structures of teeth, coral,
or seashells. The greater the number of trapped electrons, the
older the specimen. Electron spin resonance can date tooth enamel,
coral, or seashells as old as 1 million years.
Thermoluminescence
This technique measures electrons trapped in the microscopic
structure of rocks and clay and can date heated clay as old
as 70,000 years.
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