Research press release





今回、Chris Clarksonたちの研究グループは、Madjedbebe岩窟住居での新たな発掘作業の結果、2015年の発掘で見つかった人工遺物が高密度で分布する層の最下層から約11,000点の人工遺物(剥片石器、砥石、知られる限りで最古の刃先が研削された手斧など)が出土したことを報告している。Clarksonたちは、こうした人工遺物が発見された位置を注意深く評価し、人工遺物が発見された堆積物の年代と対応するようにした上で、高度な年代決定法と用いて堆積物の年代を推定した。Clarksonたちの解析結果では、この遺跡が層序学的に正確なことが確認され、深くなるほど古くなる一般的なパターンがあることが明らかになり、これまでより正確な年代決定が行われた。発掘現場で最も深い部分の年代は、約65,000年前と推定され、この地域にヒトが初めて居住した年代が約5,000年も昔にさかのぼった。


Humans first arrived in northern Australia around 65,000 years ago, according to new archaeological evidence presented in this week’s Nature. This date is earlier than estimates that had been made during previous excavations of the same site in northern Australia and predates the extinction of Australian megafauna.

The date when humans first arrived in Australia is a contested issue, with current estimates ranging from 47,000 years ago to around 60,000 years ago. A key site in this debate is Madjedbebe, a rock shelter in northern Australia, the oldest known human occupation site in Australia. Previous dates from this site had put the presence of modern humans in Australia at between 50,000 and 60,000 years ago, but concerns have been raised about the dating of the artefacts from this site.

Chris Clarkson and colleagues report the results of new excavations from the site, yielding around 11,000 artefacts in the lowest dense artefact layer from the 2015 dig, such as flaked stone tools, grinding stones and the oldest known edge-ground hatchets. The authors carefully assessed the position of the artefacts to ensure that they matched the ages of the sediments in which the artefacts were found, and the ages of the sediments were estimated using advanced dating techniques. Their analyses confirm the stratigraphic integrity of the site, showing a general pattern of increasing age with depth, and provide ages that are more accurate than before. The deepest part of the dig is estimated to be around 65,000 years old, pushing back the timing of first occupation in the region by around 5,000 years.

The results set a new minimum age for the dispersal of modern humans out of Africa and across south Asia. Moreover, the findings indicate that modern humans arrived on the continent before the extinction of Australian megafauna, an event in which the role of humans has been questioned.

doi: 10.1038/nature22968

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