Discover 4

April 2018^ DISCOVER^39

OPPOSITE FROM TOP: IMAGE COURTESY OF PROFESSOR CHRISTOPHER HENSHILWOOD; DANIELA ROSSO ET AL./JOURNAL.PONE.0164793, 2016. THIS P

AGE: DAN BISHOP/DISCOVER

of which may exist at one site but not another,

requiring archaeologists such as Zipkin to take a

shotgun approach in deciding what to look for.

“If you talk to a geologist or a chemist about

measuring something in the lab, they’ll say,

‘No problem. How much, say, selenium is in

this? OK, we can measure that,’ ” he says. “But

archaeologists are not interested in measuring

specific elements; we measure everything and

figure out later what’s relevant.”

Zipkin typically measures more than 40

elements per sample and could find up to 15 of

them useful for the fingerprinting, which creates

that site’s geochemical signature. The signatures

are added to a database which, when large enough,

can be used to determine the geographic origin of

material found at an archaeological site.

The ability to discover, by cross-checking the

database for a geochemical signature match, that

an object found at Site A was actually collected

from Site B can have huge significance, says

Zipkin. “How far material was transported can be

seen as evidence of trade or social networks.”

Elemental fingerprinting has proven particularly

important for the Olorgesailie material.

The worked pieces of ochre there, while not

fingerprinted yet, are the oldest ochre found in

the region, and were discovered with pieces of

obsidian that came from about 60 miles away.

“The ochre at Olorgesailie appears in the same

time period as a new behavior: the importing of

obsidian from distant places,” Brooks says. “This

is a radical shift in behavior.”

Modern hunter-gatherer societies typically

limestone pebble with ochre residue on one side.

The pebble appears to have been dipped into an

ochre-based paint and used as a stamp on an

unknown material.

A few thousand miles to the south and much

earlier — about 100,000 years ago — people

were using ochre in even more complex ways at

Blombos Cave in South Africa. In addition to

pieces of ochre that appear to have been engraved

— the oldest such abstract art in the world —

archaeologists have found tool kits that included

abalone shells used as containers to mix ochre with

crushed bone, charcoal, quartz and other material

to make paint.

“The Blombos Cave ‘red ochre paint factory’

represents a milestone in human cognitive

evolution,” Rifkin says.

But Blombos is not the only — or even the

earliest — such landmark moment. New research

points to humans in Kenya working ochre pieces

more than 307,000 years ago at a site called

Olorgesailie. Brooks, a senior researcher on

the Olorgesailie project, describes two roughly

finger-sized pieces of ochre that bear the marks of

human alteration — and perseverance.

“One of the pieces has been chipped with some

kind of sharp object,” Brooks says. “The other

one has grinding striations and what seems to be

attempted perforation. It looks like someone took

something like a chisel and just dug and dug.”

NETWORKING IN

THE PALEOLITHIC

In addition to its use as a stand-in for charting

human evolution, ochre also serves as a proxy for

human movement. Last July, for example, a Nature

study pushed back the earliest human presence

in Australia to at least 65,000 years ago, nearly

20,000 years earlier than previously thought.

The new date is based on thousands of artifacts

from the Northern Australia site of Madjedbebe,

including numerous examples of ochre in ground,

slab and “crayon” forms.

Thanks to a new technique called elemental

fingerprinting, ochre can also provide information

about a different kind of human movement: social

and trade networks.

“Elemental fingerprinting sounds a little CSI,

but it’s the idea that you can sort something

back to its origin,” says Zipkin, a member of the

Olorgesailie research team and a leader in the

method, which involves collecting samples of

different kinds of material from a number of sites.

The samples are then analyzed to determine the

unique geochemical signature of each site. These

signatures are made of multiple elements, some

Site A

Archaeological

Site B

Geological

Site C

Site D

Range of territory

Elemental Fingerprinting

Analyzing the unique chemical signatures of materials

tells archaeologists a lot about their origins. Finding

artifacts at site A that came from site B implies the

people of site A must have left their territory and

interacted, in some way, with the neighboring people.