The Acheulian tools at Kokiselei were found just above a sediment layer associated with a polarity interval called the "Olduvai Subchron." It is named after Tanzania's Olduvai Gorge, where pioneering work in the 1930s by Leakey's parents, Louis and Mary, uncovered a goldmine of early human fossils. In a study in Earth and Planetary Science Letters last year, Lepre and Kent found that a well-preserved Homo erectus skull found on east side of Lake Turkana, at Koobi Fora Ridge, also sat above the Olduvai Subchron interval, making the skull and Acheulian tools in West Turkana about the same age.This is not terribly unrealistic or unpredictable. We know that Homo erectus appears on the landscape between 1.78 and 1.9 million years ago and that Oldowan tools date back to almost 2.4 million years ago at the site of Gona. It does mean that cognitive jumps were being made earlier than we thought, however and broadens our understanding of the abilities of early Homo erectus.
More pieces of the puzzle.