Stone Age humans... knowingly tweaked the chemical and physical properties of an iron-containing pigment known as red ochre with the gum of acacia trees to create adhesives for their shafted tools.Archaeologists had believed the blood-red pigment--used by people in what is now South Africa about 70,000 years ago--served a decorative or symbolic purpose.
But the scientists had also suspected that the pigment may have been purposely added to improve glue that held the peoples' tools together.
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