Researchers from Tel Aviv University collected samples of charcoal used as fuel for metallurgical furnaces in the Timna Valley, located in Israel's southern desert region, during the 11th to 9th centuries BCE and examined them under a microscope. They found that the charcoal fuels used changed over time. The earlier samples contained mainly local white broom and acacia thorn trees, excellent fuel available nearby, but the quality of the firewood had deteriorated over time, with later samples consisting of low-quality wood fuel and timber imported from afar.