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| People left traces
of their presence in the sediments of a shoreline
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Human settlers made it to the Americas 30,000 years earlier than
previously thought, according to new evidence.
A team of scientists came to this controversial conclusion by dating
human footprints preserved by volcanic ash in an abandoned quarry in
Mexico.
They say the first Americans may have arrived by sea, rather than by
foot.
The traditional view is that the continent's early settlers arrived
around 11,000 years ago, by crossing a land bridge between Siberia and
Alaska.
Details of the latest findings were unveiled at the UK Royal Society's
Summer Science Exhibition.
Dr Silvia Gonzalez of Liverpool's John Moores University and her
colleagues found the footprints in the quarry, some 130km (80 miles)
south-east of Mexico City, in 2003. But they have only finished dating
them this year.
Dr Gonzalez was under no illusions that the finding would be
controversial: "It's going to be an archaeological bomb and we're up for a
fight," she said.
The team used several methods to date a variety of material from the
site near Puebla, Mexico, in order to be sure they were right about the
age.
The researchers used radiocarbon dating on shells and animal
bones in the sequences and dated mammoth teeth by a technique called
electron spin resonance. The
sediments themselves were dated by optically
stimulated luminescence.
"Some lake sediments were incorporated into the ash and were baked.
They look like small fragments of brick and these were the ones we dated
in the footprint layer. They gave us a result of 38,000 years," Dr
Gonzalez.
(Agencies) |
最新的證據(jù)顯示，人類移居美洲的歷史要比之前了解的提前3萬(wàn)年。
對(duì)保存在火山灰中的人類足跡進(jìn)行年代測(cè)定后，一個(gè)科學(xué)家小組得出了這一具有爭(zhēng)議性的結(jié)論。這些火山灰是在墨西哥一個(gè)廢棄的采石場(chǎng)被發(fā)現(xiàn)的。
他們表示，首批美洲人可能是經(jīng)由海路抵達(dá)美洲的，而非徒步遷徙過(guò)去的。
傳統(tǒng)觀點(diǎn)認(rèn)為，最初定居美洲的古人類大約在一萬(wàn)一千年前跨越西伯利亞與阿拉斯加州之間的大陸橋抵達(dá)美洲。
英國(guó)皇家社會(huì)夏季科學(xué)展覽上公布了最新發(fā)現(xiàn)的詳細(xì)資料。
來(lái)自利物浦約翰·摩爾斯大學(xué)的西爾維亞·岡薩雷斯博士和她的同事們于2003年在采石場(chǎng)發(fā)現(xiàn)了這些足跡，但是他們今年才完成了足跡的年代測(cè)定。該采石場(chǎng)位于墨西哥城東南約130公里（80英里）的地方。
岡薩雷斯博士堅(jiān)信這一發(fā)現(xiàn)將引起爭(zhēng)議，她說(shuō)：”在考古學(xué)界看來(lái)，這無(wú)疑是一枚炸彈，我們將面臨一場(chǎng)戰(zhàn)爭(zhēng)。”
該小組運(yùn)用多種方法對(duì)墨西哥普埃布拉附近遺址的各種物質(zhì)進(jìn)行了年代測(cè)定，以此確保他們得出的結(jié)果是正確的。
研究人員利用放射性碳測(cè)定法計(jì)算貝殼及動(dòng)物骨骼的年代，用電子自旋共振法測(cè)量猛犸牙齒的年代，對(duì)沉積物本身則運(yùn)用了光致發(fā)光技術(shù)進(jìn)行檢測(cè)。
岡薩雷斯博士稱：“一些湖底沉積物被摻雜到火山灰中，之后被烘烤，這些看起來(lái)好象是磚塊的碎片具有三萬(wàn)八千年的歷史，它們與足跡層屬于同一年代。”
（中國(guó)日?qǐng)?bào)網(wǎng)站譯） |
Updated: 2005-07-07 11:02
