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福建厦门市薇格医院地址They know by studying the remains of past lifepreserved in rocks, particularly sedimentary rocks.研究人员在研究岩石特别是沉积岩中保存着的生物遗骸时找到了据。These rocks are formed from particles of mudand sand, typically when they settle to the bottom of a body of water.这些岩石是由泥土和沙砾沉积在水底形成的。Fossils of organisms withhard body parts dont appear in sedimentary rock older than about 600 million years,生物体中较硬的身体部分所形成的化石不会出现在6亿年以上的沉积岩中,but theEarth is estimated to be 4.6 billion years old.但是地球预计已经有46亿年之久了。To find the oldest life, paleontologists looked for it in the oldest sedimentary rock they could find.为了寻找最古老的生命,古生物学者找到了他们可以找到的最古老的沉积岩。Sedimentary rocks dating back to Earths earliest days are rare.这些可以追溯到形成于地球初期的沉积岩是十分罕见的。Some of the oldest known areabout three and a half billion years old.目前所知的一些最古老的沉积岩大约有35亿年的历史。In these very old rocks, paleontologists have found something that looked familiar.在这些古老的岩石中,古生物学者发现了一些熟悉的东西。Certaincommunities of microbes can form layered, rock-like mounds called stromatolites.某些菌落可以形成一层一层,岩石状的土丘,被叫做叠层石。Stromatolitesgrow in shallow bodies of water in many places around the world.世界上有很多地方的浅水区都存在着叠层石。In the 1980′s paleontologistsfound the remains of ancient stromatolites in 3.5 billion year old sedimentary rocks.在20世纪80年代的时候,古生物学家在35亿年的沉积岩里发现了古叠层石的遗骸。Besides stromatolites, possible microscopic fossils have been found in rocks up to 3.5 billion yearsold.除了叠层石外,其他目前在岩石中已经找到的可能的微观化石已经有长达35亿年的历史了。While the origin of these tiny structures is still intensely debated, many scientists areconvinced that they are the remains of microorganisms.虽然关于这些微小结构的起源还存在着严重的分歧,但很多科学家已经确认,他们是微生物的残骸。It appears that by at least 3.5 billion yearsago, the oceans were teeming with life, and that the land was also colonized by microbes veryearly in Earths history.似乎在地球演变的早期过程中,至少在35亿年以前,海洋里存在着大量生体命,而陆地是微生物的主要栖息地。 201407/314218厦门Vmax薇格整形医院网上挂号 When you go back to work or class after lunch, why is it so hard to stay awake?当我们用完午餐回去工作或上课时,为什么很难保持清醒呢?Although we get energy from food, we also use lots of energy to digest it. Your energy use increases 25-50% as you digest a meal.尽管我们从食物中获取能量,但也需要耗费许多能量来消化这些食物。消化一餐就会增加百分之二十五至五十的能量消耗。With all that action going on in the digestive system, the body sends extra blood to the gut to supply oxygen and other necessities.有了消化系统内的一系列活动,身体才能源源不断地将额外的血液输送到消化道以提供充足的氧气和其它必需物。How does the body know when to do this?身体如何知道何时这样做?As food enters the stomach, the intestines secrete substances that dilate, or expand, the blood vessels that supply them with blood.当食物进入胃,肠道便分泌许多物质,它们使得为肠道供血的血管膨胀或扩张。As a result, more blood flows to the upper digestive tract, and there’s a bit less to go around to the rest of the body.结果便是更多的血液流向上消化道,而循环于身体其它部分的血液则相应减少,That might make your arms and legs and brain feel a little sluggish!这时你可能感觉浑身懒洋洋的,连大脑也变得迟钝起来。At the same time, the small intestine releases a hormone that activates the part of the brain that controls sleep, making you drowsy.同时,小肠释放出一种荷尔蒙,它可以激活控制睡眠的大脑区域,让你昏昏欲睡。Finally, the natural components in foods can also contribute to the snooze effect. Certain foods, especially carbohydrates, increase production of serotonin in the brain.最后,食物中的天然成分也会让你打盹。某些食物,特别是碳水化合物,会增加大脑中血清素的生成。Serotonin works both to stop sugar craving, and to make you very relaxed. The larger the meal, the more pronounced that feeling can be.血清素既可以抑制吃甜食的欲望,又可让你倍感放松。吃得越多,这种感觉就越明显。With all of these physiological reasons why we might feel sleepy after eating, a siesta after lunch sounds like a brilliant idea, and maybe after dinner and breakfast too!鉴于诸多生理原因导致我们餐后昏昏欲睡,也许午餐抑或早晚餐后小憩一会儿是个明智的选择。 /201306/243199厦门薇格医疗美容韩式三点多少钱

厦门祛斑医院Until recently, when scientists studied changes in open-ocean ecosystems, they looked at changes in the bottom of the food chain that gradually make their way to the top, like foodshortages and shifts in the ocean environment.直到最近,当科学家们在研究远洋地区生态系统的变化时,他们观察了处于食物链最底层并且在慢慢上升的变化,比如说食物短缺、海洋环境的变化。A recent study,however, suggests that more attention needs to be given totop-down influences as well.然而,最近的一项调查显示,人们还应该更多的注意自上而下的影响。For example, over the past few decades, theres been a major collapse of the populations ofharbor seals, fur seals, sea lions, and sea otters living on the coasts of western Alaska.比方说,在过去的几十年里,生活在阿拉斯加西海岸的斑海豹、海、海狮和海獭数量极具下降。Now a newstudy suggests that all this destruction can be traced back to humans overfishing sperm andbaleen whales between 1946 and 1979.现在,一项新的调查显示,所有的这些毁坏都可以归咎于人类在1946年到1979年期间过度捕捞抹香鲸和须鲸。Killer whales, who live at the top of the ocean food chain, used to prey on sperm and baleenwhales.虎鲸是在海洋食物链的最高层,它习惯于捕食抹香鲸和须鲸。When these were no longer available, the killer whales were forced to fish farther down the food chain.当虎鲸不能再捕食它们的时候,它就被迫捕食处于更下一层的食物链。First they fed on seals, which were the easiest to catch and the most nutritionallyvaluable.她们先捕食的是最容易捕捉且最有营养价值的海豹。Then, when seals became rare, the killer whales turned to sea lions.接着,当海豹变得稀少后,虎鲸便转向了海狮。When the sea lionpopulation crashed, they started fishing sea otters.而又当海狮的数量变少后,虎鲸又开始猎杀海獭了。The domino effect reaches even farther.多米诺效应又继续延伸。Without sea otters keeping sea urchins in check, their population has exploded.没了海獭约束海胆,海胆的数量变得庞大起来。And theyvedestroyed the kelp forests, and with it, the kelp forest ecosystem in southwestern Alaska.并且破坏阿拉斯加啊西南部的海藻林生态系统。Animals switching food sources can have a very serious effect on the environment.动物间交换食物来源对环境有着很严重的影响。And thatwe humans, as the ultimate predators, need to give a lot of thought to the choices we make.而作为终极捕食者,人类需要好好思考一下他们所做的选择。They may affect the food web in unintended ways.这些选择可能会以人们所不知道的方式来影响食物网。 201405/301199 厦门薇格医疗整形美容医院隆胸多少钱福建省厦门薇格整形医院网上咨询



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