a new study suggests that homo erectus（直立人） , a 1（先驱） to modern humans, was using advanced toolmaking methods in east africa 1.8 million years ago, at least 300,000 years earlier than 2 thought. the study, recently published in nature, raises new questions about where these tall and slender early humans originated and how they developed sophisticated tool-making technology. homo erectus appeared about 2 million years ago, and ranged across asia and africa before hitting a possible 3 dead-end, about 70,000 years ago. some researchers think homo erectus evolved in east africa, where many of the oldest fossils have been found, but the discovery in the 1990s of equally old homo erectus fossils in the country of georgia has led others to suggest an asian origin. the study in nature does not resolve the debate but adds new 4. at 1.8 million years ago, homo erectus in dmanisi, georgia was still using simple chopping tools while in west turkana, kenya, according to the study, the population had developed hand axes, picks and other 5 tools that anthropologists（人类学家） call "acheulian."
"the acheulian tools represent a great 7 leap," said study co-author dennis kent, a 8 with 9 appointments at rutgers university and columbia university's lamont-doherty earth 10. "why didn't homo erectus take these tools with them to asia?"
in the summer of 2007, a team of french and american researchers traveled to kenya's lake turkana in africa's great 11 valley, where earth's plates are tearing apart and some of the earliest humans first appear. 6 richard leakey's famous find--turkana boy, a homo erectus teenager who lived about 1.5 million years ago -- was 12（挖掘） on lake turkana's western shore and is still the most complete early human skeleton found so far.
six miles from turkana boy, the researchers headed for kokiselei, an archeological（考古学的） site where both acheulian and simpler "oldowan" tools had been found earlier. their goal: to establish the age of the tools by dating the surrounding 14. past flooding in the area had left behind layers of 15 and clay that hardened into mudstone, preserving the direction of earth's magnetic field at the time in the stone's magnetite grains. the researchers 16 away 17 of the mudstone at kokiselei to later 18 the periodic polarity reversals and come up with ages. at lamont-doherty's paleomagnetics lab, they compared the magnetic 20 with other stratigraphic（地层的） records to date the archeological site to 1.76 million years.
"we suspected that kokiselei was a rather old site, but i was taken aback when i realized that the geological data indicated it was the oldest acheulian site in the world," said the study's lead author, christopher lepre, a geologist who also has joint appointments at rutgers and lamont-doherty. the oldest acheulian tools previously identified appear in konso, ethiopia, about 1.4 million years ago, and india, between 1.5 million and 1 million years ago.
the acheulian tools at kokiselei were found just above a 13 layer associated with a polarity（极性，对立） 19 called the "olduvai subchron." it is named after tanzania's olduvai 21, 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 22 found on east side of lake turkana, at koobi fora 23, also sat above the olduvai subchron interval, making the skull and acheulian tools in west turkana about the same age.
收听单词发音 
