古印度人定居北美早于预计时间
文章来源:未知 文章作者:enread 发布时间:2011-03-25 02:57 字体: [ ]  进入论坛
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Researchers excavating1(挖掘) a creek2(小溪) bed in central Texas have found evidence suggesting humans settled in North America some two thousand years earlier than previously3 estimated. The findings are reported in the March 25 issue of Science.

Earth scientists at the University of Illinois at Chicago determined4 the age using an optical dating technique. They linked sediment5 and mineral samples to human artifacts(史前古器物) and tools found in a single stratigraphic layer located below younger, previously dated Paleo-Indian Clovis-culture artifacts.

Texas A&M University anthropologist6(人类学家) Michael Waters led the archaeological dig in the Buttermilk Creek complex, near Austin, which has been excavated7 for years. While artifacts suggesting earlier settlement had been found at the site before, they couldn't be verifiably dated.

UIC earth and environmental sciences professor Steven Forman worked with Waters and a multi-university team of researchers, finding buried beneath the Clovis layer tools such as blades and cores -- technologies unique to the Clovis culture.

Forman gathered about 50 core samples from two sites at Buttermilk Creek for luminescence(发冷光) dating analysis at UIC. Carbon-14 dating couldn't be used to date the pre-Clovis artifact layer because that layer didn't contain any organic matter.

"We dated the sediments8 by a variety of optical methods," Forman said. "We also dated different mineral fractions as well, and we consistently got the same ages. We looked at the age structure of the sediment by many different ways and got the same answers."

This is the first time that optical dating has been used to constrain9 a paleoculture within a date range, Forman said.

Luminescence dating, a relatively10 new technique, measures light energy trapped in minerals such as feldspar(长石) and quartz11 formed centuries ago. Samples must be carefully handled to avoid any exposure to light, which would contaminate(污染) the readings. They were analyzed12 in a darkroom laboratory at UIC.

"We found Buttermilk Creek to be about 15,500 years ago -- a few thousand years before Clovis," Forman said. "It's the first identification of pre-Clovis lithic technology (stone tool technology) in North America."



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1 excavating 5d793b033d109ef3f1f026bd95b1d9f5     
v.挖掘( excavate的现在分词 );开凿;挖出;发掘
参考例句:
  • A bulldozer was employed for excavating the foundations of the building. 推土机用来给楼房挖地基。 来自《简明英汉词典》
  • A new Danish expedition is again excavating the site in annual summer digs. 一支新的丹麦探险队又在那个遗址上进行一年一度的夏季挖掘。 来自辞典例句
2 creek 3orzL     
n.小溪,小河,小湾
参考例句:
  • He sprang through the creek.他跳过小河。
  • People sunbathe in the nude on the rocks above the creek.人们在露出小溪的岩石上裸体晒日光浴。
3 previously bkzzzC     
adv.以前,先前(地)
参考例句:
  • The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
  • Let me digress for a moment and explain what had happened previously.让我岔开一会儿,解释原先发生了什么。
4 determined duszmP     
adj.坚定的;有决心的
参考例句:
  • I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
  • He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。
5 sediment IsByK     
n.沉淀,沉渣,沉积(物)
参考例句:
  • The sediment settled and the water was clear.杂质沉淀后,水变清了。
  • Sediment begins to choke the channel's opening.沉积物开始淤塞河道口。
6 anthropologist YzgzPk     
n.人类学家,人类学者
参考例句:
  • The lecturer is an anthropologist.这位讲师是人类学家。
  • The anthropologist unearthed the skull of an ancient human at the site.人类学家在这个遗址挖掘出那块古人类的颅骨。
7 excavated 3cafdb6f7c26ffe41daf7aa353505858     
v.挖掘( excavate的过去式和过去分词 );开凿;挖出;发掘
参考例句:
  • The site has been excavated by archaeologists. 这个遗址已被考古学家发掘出来。
  • The archaeologists excavated an ancient fortress. 考古学家们发掘出一个古堡。 来自《简明英汉词典》
8 sediments 8b3acb612b624abdf2c2881bc6928565     
沉淀物( sediment的名词复数 ); 沉积物
参考例句:
  • When deposited, 70-80% of the volume of muddy sediments may be water. 泥质沉积物沉积后,体积的70-80%是水。
  • Oligocene erosion had truncated the sediments draped over the dome. 覆盖于穹丘上的沉积岩为渐新世侵蚀所截削。
9 constrain xpCzL     
vt.限制,约束;克制,抑制
参考例句:
  • She tried to constrain herself from a cough in class.上课时她竭力忍住不咳嗽。
  • The study will examine the factors which constrain local economic growth.这项研究将考查抑制当地经济发展的因素。
10 relatively bkqzS3     
adv.比较...地,相对地
参考例句:
  • The rabbit is a relatively recent introduction in Australia.兔子是相对较新引入澳大利亚的物种。
  • The operation was relatively painless.手术相对来说不痛。
11 quartz gCoye     
n.石英
参考例句:
  • There is a great deal quartz in those mountains.那些山里蕴藏着大量石英。
  • The quartz watch keeps good time.石英表走时准。
12 analyzed 483f1acae53789fbee273a644fdcda80     
v.分析( analyze的过去式和过去分词 );分解;解释;对…进行心理分析
参考例句:
  • The doctors analyzed the blood sample for anemia. 医生们分析了贫血的血样。 来自《简明英汉词典》
  • The young man did not analyze the process of his captivation and enrapturement, for love to him was a mystery and could not be analyzed. 这年轻人没有分析自己蛊惑著迷的过程,因为对他来说,爱是个不可分析的迷。 来自《简明英汉词典》
TAG标签: human culture America
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