The most powerful evidence comes from Kalambo Falls in Zambia where many things related to the use of fire by humans had been found , like charred wood , charcoal , reddened areas , carbonized grass stems and plants , and wooden implements which may have been hardened by fire . The strongest evidence comes from Kalambo Falls in Zambia where several artifacts related to the use of fire by humans had been recovered including charred logs , charcoal , reddened areas , carbonized grass stems and plants , and wooden implements which may have been hardened by fire .