英語聽力：美洲大平原-5

Mud from the ancient riverbanks is good for building nests. lt also holds more evidence that will help us to reconstruct the ice age past.

Every now and then,new clues surface, hinting at what else might lie beneath. ln this dried-up pond in South Dakota, known as Hot Springs, scientists unearthed great piles of bones. What kind of creature died here? The bones reveal it stood four metres tall and weighed more than 10 tonnes. There's nothing fitting that description living here today.

Here's the give-away, a pair of tusks two metres long, the trademark of a Columbian mammoth, the biggest animal to roam the ice age plains. By comparing it to elephants in Africa today, can we shed light on how those ice age elephants lived and what they lived on?

These are mammoth teeth, huge molars the size of bricks. They have deep ridges very similar to those of modern elephants, suggesting mammoths, too, survived by grinding vast amounts of grass.

Plant fragments trapped between the ridges can still be identified today. Thousands of years after this mammoth died, we know exactly what it ate for its last meal. Grass is a tough, abrasive food. Even with protective enamel ridges, these teeth would gradually have worn down. But just like modern elephants, the mammoths had evolved a way to deal with this. As one set of teeth was eroded8, another grew up to take its place. The evidence suggests they had six sets in all, to last a lifetime, up to 60 years.

The South Dakota mammoth didn't make it to old age and it was not alone. The site turned out to be a mammoth graveyard9, hiding more than 50 skeletons, all from animals in their prime. There's no sign they were killed by hunters, so how did so many healthy mammoths die?

1 unearthed

出土的(考古)

參考例句：

Many unearthed cultural relics are set forth in the exhibition hall. 展覽館里陳列著許多出土文物。

Some utensils were in a state of decay when they were unearthed. 有些器皿在出土時已經(jīng)殘破。

2 tusks

n.(象等動物的)長牙( tusk的名詞復數(shù) );獠牙;尖形物;尖頭

參考例句：

The elephants are poached for their tusks. 為獲取象牙而偷獵大象。

Elephant tusks, monkey tails and salt were used in some parts of Africa. 非洲的一些地區(qū)則使用象牙、猴尾和鹽。 來自英語晨讀30分(高一)

3 trademark

n.商標;特征;vt.注冊的…商標

參考例句：

The trademark is registered on the book of the Patent Office.該商標已在專利局登記注冊。

The trademark of the pen was changed.這鋼筆的商標改了。

4 mammoth

n.長毛象;adj.長毛象似的，巨大的

參考例句：

You can only undertake mammoth changes if the finances are there.資金到位的情況下方可進行重大變革。

Building the new railroad will be a mammoth job.修建那條新鐵路將是一項巨大工程。

5 ridges

n.脊( ridge的名詞復數(shù) );山脊;脊狀突起;大氣層的)高壓脊

參考例句：

The path winds along mountain ridges. 峰回路轉(zhuǎn)。

Perhaps that was the deepest truth in Ridges's nature. 在里奇斯的思想上，這大概可以算是天經(jīng)地義第一條了。

6 abrasive

adj.使表面磨損的;粗糙的;惱人的

參考例句：

His abrasive manner has won him an unenviable notoriety.他生硬粗暴的態(tài)度讓他聲名狼藉。

She had abrasions to her wrists where the abrasive rope had scraped her.她的手腕有多出磨傷，那是被粗糙的繩子擦傷的。

7 enamel

n.琺瑯，搪瓷，瓷釉;(牙齒的)琺瑯質(zhì)

參考例句：

I chipped the enamel on my front tooth when I fell over.我跌倒時門牙的琺瑯質(zhì)碰碎了。

He collected coloured enamel bowls from Yugoslavia.他藏有來自南斯拉夫的彩色搪瓷碗。

8 eroded

adj. 被侵蝕的，有蝕痕的 動詞erode的過去式和過去分詞形式

參考例句：

The cliff face has been steadily eroded by the sea. 峭壁表面逐漸被海水侵蝕。

The stream eroded a channel in the solid rock. 小溪在硬石中侵蝕成一條水道。

9 graveyard

n.墳場

參考例句：

All the town was drifting toward the graveyard.全鎮(zhèn)的人都象流水似地向那墳場涌過去。

Living next to a graveyard would give me the creeps.居住在墓地旁邊會使我毛骨悚然。