Monday, December 22, 2008

Earliest evidence of cave-dwelling humans.

A research team led by Professor Michael Chazan, director of the University of Toronto's Archaeology Centre, has discovered the earliest evidence of our cave-dwelling human ancestors at the Wonderwerk Cave in South Africa.
Stone tools found at the bottom level of the cave — believed to be 2 million years old — show that human ancestors were in the cave earlier than ever thought before. Geological evidence indicates that these tools were left in the cave and not washed into the site from the outside world.
Archaeological investigations of the Wonderwerk cave — a South African National Heritage site due to its role in discovering the human and environmental history of the area — began in the 1940s and research continues to this day.

Wonderwerk Cave: Basic Information

Location: Northern Cape Province, South Africa between Danielskuil and Kuruman
How did the Cave Form: The cave formed by water action in the Dolemite rocks of the
Asbestos Hills. This rock formation is over 2 billion years old, some of the oldest rock
on earth, so we do not know when exactly the cave formed.

Basic properties of the cave; The cave runs 130 meters from front to back.
How was Wonderwerk discovered: Local farmers dug up large parts of the cave in the
1940’s to sell the sediments for fertilizer. Subsequently a series of brief archaeological
excavations began. Peter Beaumont of the McGregor Museum carried out major
excavations at the site between 1978-1993.

The Discovery
Using a combination of dating methods it has been possible to date the bottom level
reached by Peter Beaumont in the front part of the cave to 2 million years ago.
A small number of very small stone tools have been recovered from excavations in this

Geological evidence indicates that these tools were deposited in the cave by human
ancestors, not washed into the site from the outside.

The combination of stone tools indicating the presence of human ancestors and the dating
of the level leads to the conclusion that human ancestors (hominids) were in the cave 2
million years ago.

This is the earliest evidence for intentional cave occupation by human ancestors.
There were a number of species of hominids in southern Africat 2 million years ago. The
most likely candidate as the manufacturer of the stone tools found at Wonderwerk is
Homo habilis.

The oldest known stone tools from sites in Ethiopia date to 2.4 million years. The
Wonderwerk Cave discoveries are those close in age to the very earliest known stone
tools and similar in date to the bottom levels at Olduvai Gorge.

How Was the Site Dated
The deposits at Wonderwerk Cave built up over time so that the deeper one excavates the
layers become older. The trick is to figure out exactly how old the levels are.
We used two methods that together provide a secure date.

For Paleomagnetic Dating Hagai Ron of the Hebrew University took small samples of
soil from the entire sequence (over fifty samples). These samples allow him to measure
changes in he earth’s magnetic field and to correlate the Wonderwerk sequence with a
global timescale for changes in the magnetic field (known as reversals).

For Cosmogenic Burial Age Ari Matmon, also from the Hebrew University, took soil
samples and carefully prepared them in the lab. He then sent these samples to an atomic
accelerator in the United States where a procedure to measure isotopes, much like the
method used in carbon dating, was carried out. Unlike carbon dating, Cosmogenic Burial
Age dating can provide very old dates.

Why was this so difficult? Most well dated early sites are in East Africa where there are
volcanic ash layers that can be dated using the Argon method. In southern Africa we
lack these ash layers so that we need to develop new methods. The first use of
Cosmogenic Burial Age dating in South Africa was at the Cradle of Humankind. Our
results show the value of this method, particularly when combined with Paleomagnetic
dating, for archaeological research both in the region and globally.

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