An­cient camps full of data

Pilbara News - - News -

■ Ra­dio car­bon data from pre­his­toric oc­cu­pa­tion sites are pro­vid­ing in­sights into Aus­tralia’s fluc­tu­at­ing hu­man pop­u­la­tion lev­els tens of thou­sands of years ago.

Aus­tralian Na­tional Univer­sity ar­chae­ol­o­gist Alan Wil­liams used ra­dio car­bon-dat­ing tech­nol­ogy to ex­am­ine char­coal dates from more than 1000 pre­his­toric camp­fires and based on this he says pop­u­la­tions ap­pear to have in­creased steadily un­til 25,000 years ago.

He did this by ex­am­in­ing the iso­tope Car­bon 14, which is ab­sorbed by all liv­ing things from the at­mos­phere.

Their re­mains then lose the iso­tope at a steady rate af­ter they die, and Car­bon 14 lev­els pro­vide re­li­able dates for any or­ganic mat­ter up to about 35,000 years old.

Dr Wil­liams com­pared these dates with cli­matic change pro­files pro­vided by a re­cent syn­the­sis of Aus­tralia’s palaeo­cli­mate from the Aus­tralasian In­te­gra­tion of Ice core, Marine and Ter­res­tial records pro­ject.

Co-au­thor UWA ar­chae­ol­o­gist Winthrop Pro­fes­sor Peter Veth says Dr Wil­liams’ com­par­i­son showed a clear cor­re­la­tion be­tween datasets.

“De­mo­graphic mod­els sug­gest pop­u­la­tions may have been quite high be­fore the last ice age,” he said.

Af­ter this ini­tial in­crease, he said, pop­u­la­tion lev­els re­mained steady or even de­clined from 25,000 years ago, dur­ing the more arid Last Gla­cial Max­i­mum (25,000 to 13,000 years ago) when tem­per­a­tures were about ten de­grees cooler.

This in­cluded ar­chae­o­log­i­cal “si­lences” — or lack of oc­cu­pa­tion data — within Aus­tralia’s arid zone dur­ing the Last Gla­cial Max­i­mum.

“There are re­ally only smaller biore­gions in the arid zone where their oc­cu­pa­tion ceases to be reg­is­tered,” Winthrop Pro­fes­sor Veth said.

“Then with the re­struc­ture in pop­u­la­tion and pos­si­bly lower car­ry­ing ca­pac­ity for large por­tions of the con­ti­nent that be­came more arid, pop­u­la­tion lev­els of de­mog­ra­phy may have ac­tu­ally be­come more neg­a­tive.”

Camp­fire num­bers be­gan to grow again 13,000 years ago when the north­ern wet sea­son reemerged.

In the west Pil­bara’s Chich­ester Range, for ex­am­ple, ra­dio­car­bon dat­ing shows peo­ple started to use rock shel­ters that had been un­oc­cu­pied since the late Pleis­tocene (up to 11,700 years ago).

Winthrop Pro­fes­sor Veth said while pop­u­la­tion lev­els, oc­cu­pa­tion pat­terns and over­all cli­mate trends cor­re­lated strongly from 35,000 un­til about 5000 years ago, things then be­came less pre­dictable.

He said Abo­rig­i­nal peo­ple started to em­brace tech­nolo­gies and prac­tices that ap­pear to have made their be­hav­iour less de­pen­dent on easily avail­able re­sources.

For ex­am­ple, they re­mained more seden­tary by wet-milling grass and aca­cia seeds to pre­pare damper and seed cakes.

Pic­ture: Chris Lees

Ar­chae­ol­o­gist Alan Wil­liams used ra­dio car­bon-dat­ing tech­nol­ogy to ex­am­ine char­coal dates from 1000 pre­his­toric camp­fires.

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