當你真正想完成一件事時，根本不會在意別人是否看到。備考漫漫長路，和你一起默默地走下去。以下是“GRE閱讀材料練習：樹木的年輪判斷其年齡”，一起來看看吧！
    
    Not always the ring of truth.The use of wood to assess past environments needs care.TREE rings are Mother Nature's history books.Researchers often look at chemicals stored in them when trying to reconstruct past environments.Like all history books, though, they can be unreliable.And in the case of one particular chemical of interest, mercury, Jose Antonio Rodriguez Martin of the National Institute for Agricultural and Food Research and Technology, in Madrid, and his colleagues have just shown how unreliable they are.
    年輪不一定反映事實通過樹木判斷過去的環(huán)境時要小心了年輪是大自然的史書。在試圖重現(xiàn)過去的環(huán)境時，研究人員經(jīng)常會從年輪中所含的化學物質(zhì)入手。然而就和所有的史書一樣，年輪也并不怎么靠譜。通過其關(guān)注的一個特別的化學物質(zhì)-汞，西班牙國家農(nóng)業(yè)與食物研究及技術(shù)學會的何塞·安東尼奧·羅德里格斯·馬丁及其同事便剛剛證明了年輪多么不靠譜。
    Dr Rodriguez Martin was studying pines on La Palma, in the Canary Islands.He knew that Hoyo Negro, one of the island's volcanoes, had erupted violently in 1949, and believed that the clouds of ash and explosive ejections of rock from the eruption had destroyed all of the pines nearby.However, as he describes in Naturwissenschaften, when he and his team examined the area, they were stunned to discover a revenant from this cataclysm just 50 metres from the crater.
    羅德里格斯·馬丁博士一直在研究拉帕爾馬島上的松樹。他知道該島上的霍約內(nèi)格羅火山曾于1949年發(fā)生過劇烈噴發(fā)，并認為噴發(fā)產(chǎn)生的火山灰及迸散的巖石摧毀了附近所有的松樹。然而，正如他在《自然科學》雜志上所說，當他和自己的團隊對該區(qū)域進行調(diào)查時，在離火山口僅50米的地方發(fā)現(xiàn)了一棵劫后余生的松樹，讓他們震驚不已。
    Like a battle-scarred soldier, this now-great pine had many half-healed wounds in its trunk.It had survived those. It did not, however, survive Dr Rodriguez Martin's axe.He reluctantly felled it and, for comparison, collected a tree of similar age that was growing 400 metres from the eruption site, and another that was 16km away.
    One unpleasant element often ejected in volcanic eruptions is mercury.That was certainly the case in 1949, as soil-sampling showed.
    就像一名身經(jīng)百戰(zhàn)的士兵，這棵現(xiàn)已長成參天大樹的松樹的樹干上疤痕累累。這些傷口沒讓它倒下，但卻沒有逃過羅德里格斯·馬丁博士的斧頭。羅德里格斯·馬丁博士忍痛將它放倒，并分別從離噴發(fā)點400米及16千米處砍倒兩棵與其樹齡相同的松樹進行比較?；鹕絿姲l(fā)時經(jīng)常會噴 射出一種不怎么好的元素-汞。正如土壤采樣所示，1949年的火山噴發(fā)確實釋放出了汞元素。
    The question was, how much of it had got into the trees·Mercury falling.When he analysed the survivor's scar tissue Dr Rodriguez Martin found high levels of the metal in it:more than 22 micrograms per kilogram of wood.That was not surprising, given that this tissue would have formed soon after the eruption.What was surprising was that the wood of the survivor tree's rings had only 2.3 micrograms of mercury per kilogram in it.
    但問題是，有多少進入了樹體中?脫落的汞當羅德里格斯·馬丁博士分析了這棵幸存的樹上的疤痕組織后，他發(fā)現(xiàn)其中的汞元素含量很高：每公斤木材中超過22毫克。這并不出人意料，因為該組織是在火山噴發(fā)不久后形成的。出人意料的是這棵幸存的樹中年輪的木質(zhì)中每公斤僅含2.3毫克汞。
    More surprising still, the rings of the other two trees were mercury-free, despite there being mercury in nearby soil.Tree rings are made of tissue called xylem.This is a set of channels that carry water and minerals from the soil to the leaves, so its composition might be expected to reflect what is in the soil.A second set of channels, the phloem, found just under a tree's bark, carries the products of photosynthesis to the roots.
    更讓人大跌眼鏡的是，其他兩棵書的年輪中汞含量為零，盡管其附近的土壤中含有汞。構(gòu)成年輪的組織被稱為木質(zhì)部。這是從土壤中將水合礦物質(zhì)輸送至葉片的一組通道，所以其組分應該能夠反映出土壤中的組分。第二組通道叫韌皮部，就長在樹皮之下，它將光合作用的產(chǎn)物輸送到樹的根部。
    This tissue, however, is not preserved from year to year.When Dr Rodriguez Martin sampled the phloem of the trees he had chopped down, he found it much richer in mercury than their xylem.Phloem from the tree at the eruption site had 9.5 micrograms of the metal per kilogramThe two more distant trees had 2.9 and 2.0 respectively.The explanation for the discrepancy lay in the trees' bark.
    然而該組織每年都會更新。羅德里格斯·馬丁博士對被他砍倒的樹的韌皮部采樣后，他發(fā)現(xiàn)韌皮部的汞含量比木質(zhì)部的要高。位于噴發(fā)點的樹上的韌皮部中每千克含有9.5毫克汞。另外兩棵較遠的樹的韌皮部每千克汞含量分別為2.9及2.0。產(chǎn)生這種差異的原因就藏在樹皮之中。
    This had similar mercury levels to the phloem.What Dr Rodriguez Martin reckons is going on is that trees are using their bark, which they shed continually, as a waste-disposal system.Mercury is carried there by the phloem and selectively deposited in it, rather than in the plants' more permanent parts.The metal is then got rid of when the bark is sloughed off.
    樹皮的汞含量與韌皮部相近。羅德里格斯·馬丁博士認為是這么回事：樹木將其不斷脫落樹皮當做一種廢物處理系統(tǒng)。汞通過韌皮部被轉(zhuǎn)運到樹皮中，有選擇性地在其中沉積，而非在自己不易更新的部位沉積。然后當樹皮脫落時，其中的汞也隨之被除去。
    That makes it invisible to researchers who come along later. What happens to mercury, moreover, might well happen to other toxic materials.That could throw the calculations of palaeoecologists severely out of kilter.All of which is a caution to those who read the Book of Tree Rings for clues to what happened in the past.Trees, it seems, are as good as rewriting history as people are.
    這使隨后而來的研究人員無法發(fā)現(xiàn)汞的存在。而且，在汞身上出現(xiàn)的情況很可能也會出現(xiàn)在其他有毒物質(zhì)上。這會讓古生態(tài)學家的推測嚴重失準。對于那些在年輪史書中尋找線索來了解過去發(fā)生了什么的人來說，所有這些都是一個警示。樹木，似乎和人一樣精于改寫歷史。