【每日阅读训练第四期——速度越障3系列】【3-09】科技-exobiology

babybearmm

[计时一]

Introduction to Exobiology

You're driving in your car down dark road late one night with your friends. All of a sudden, you see a large circular object with blue lights spinning right in front of your car. A bright spotlight shines down on your car for ten seconds, and then leaves. As the object disappears before your eyes, you are left in amazement, wondering what just happened. Was that really a UFO? Is there really intelligent life out there in the universe? You turn around to ask your friends, only to find that one of them is missing.

Sound a little farfetched? OK. How about something a little more down to Earth.

You just got back from a two week vacation in Hawaii with your family. You walk into your room, throw down your suitcase, and sit on your bed. You glance over at the lamp on the table next to your bed. Reaching over to turn on the lamp, you notice a rather unpleasant smell. Looking down, there is a half full glass of what once might have been juice, but now is a nice bluish-green color with fuzz all around the edges. Yuck! Where did that come from?

Scientists have been asking these same questions for a long time now. Come explore the field of exobiology, the search for the origin of life on the Earth, and in the Universe.

Where would you like to go?

[238 words]

[计时二]
Pre-biotic Earth

In order to attempt to understand how life started billions of years ago, we need to first look at what scientists believe to be the conditions of our pre-biotic earth. It all started about five billion years ago. Our solar system was filled with hot gases and dust, which swirled and revolved around a white hot core. When the core approached one million degrees Fahrenheit, our sun was born. The gaseous dust clouds gradually condensed and formed asteroids. It is estimated that over 100 trillion planetesimals, or large asteroids, existed when our solar system was formed. (Picture) As these huge pieces of matter were revolving around the sun, many of them collided with one another. While some of these collisions destroyed the planetesimals, others caused them to combine. As their mass increased, gravity pulled in more particles and debris, and the planetesimals grew larger. This process, called accretion, is how the earth and the other planets were formed.

Over hundreds of millions of years, the earth continued to change due to the bombardment of asteroids.

These asteroids released such an enormous amount of energy upon impact that they began to melt the earth's crust. Radioactivity from the earth's core also changed the surface of the earth. Radioactive decay caused heat and gases to build up in the earth's core. This caused huge volcanoes to spew forth molten rock, or lava, as well as various gases which had been trapped under the surface of the earth. As this lava covered the earth, evidence of the early craters began to be erased.

[266 words]

[计时三]

As the planet earth continued to be hit by meteorites, cosmic H2O was released from the meteorites and from the crust of the earth. This gaseous H2O rose into the atmosphere, combined with CO2 and other gases, and formed incredibly dense clouds above the earth. These clouds formed a reflective shield above the earth, keeping solar heat from penetrating to the surface. As the frequency of meteorite impacts declined, the surface of the earth began to cool. When this happened, the immense clouds which had emerged began to pour rain over the entire planet, cooling the molten rock, and creating lakes and oceans. Water and wind from the atmosphere slowly began to erase the enormous craters which covered the earth.

For a long time it was thought that the early Earth had a reducing atmosphere. A reducing atmosphere contains reductants, or molecules saturated with hydrogen atoms, which are able to reduce other molecules. Many scientists believed that the atmosphere consisted of CH4, NH3, and H2. This is the mixture of gases Miller and Urey used in 1953 to mimic the conditions of the early earth. Their experiment showed that abiotic molecules could be used to create important biotic compounds thought to be necessary for the origin of life.

However, most of the scientific community now believes that the early Earth's atmosphere was not reducing. Instead, scientists believe the atmosphere was full of oxidants, such as CO2 and N2. An oxidizing atmosphere is essentially neutral, and does not permit organic chemistry to occur.

There is much known about the environment and composition of the early earth. However, there is even more which is uncertain and not known. Because of this, scientists are studying and searching for the conditions which they believe were present when life began. If we know these conditions then perhaps we can discover the building blocks from which life came.

In the next section, we will look at the Miller/Urey experiment which inspired a generation of scientific experiments in order to discover how life began.

[341 words]

[attachimg]102473[/attachimg]

[计时四]

Miller/Urey Experiment

By the 1950s, scientists were in hot pursuit of the origin of life. Around the world, the scientific community was examining what kind of environment would be needed to allow life to begin. In 1953, Stanley L. Miller and Harold C. Urey, working at the University of Chicago, conducted an experiment which would change the approach of scientific investigation into the origin of life.

Miller took molecules which were believed to represent the major components of the early Earth's atmosphere and put them into a closed system

The gases they used were methane (CH4), ammonia (NH3), hydrogen (H2), and water (H2O). Next, he ran a continuous electric current through the system, to simulate lightning storms believed to be common on the early earth. Analysis of the experiment was done by chromotography. At the end of one week, Miller observed that as much as 10-15% of the carbon was now in the form of organic compounds. Two percent of the carbon had formed some of theamino acids which are used to make proteins. Perhaps most importantly, Miller's experiment showed that organic compounds such as amino acids, which are essential to cellular life, could be made easily under the conditions that scientists believed to be present on the early earth. This enormous finding inspired a multitude of further experiments.

In 1961, Juan Oro found that amino acids could be made from hydrogen cyanide (HCN) and ammonia in an aqueous solution. He also found that his experiment produced an amazing amount of the nucleotide base, adenine. Adenine is of tremendous biological significance as an organic compound because it is one of the four bases in RNA and DNA. It is also a component of adenosine triphosphate, or ATP, which is a major energy releasing molecule in cells. Experiments conducted later showed that the other RNA and DNA bases could be obtained through simulated prebiotic chemistry with a reducing atmosphere.

[318 words]

[计时五]

These discoveries created a stir within the science community. Scientists became very optimistic that the questions about the origin of life would be solved within a few decades. This has not been the case, however. Instead, the investigation into life's origins seems only to have just begun.

There has been a recent wave of skepticism concerning Miller's experiment because it is now believed that the early earth's atmosphere did not contain predominantly reductant molecules. Another objection is that this experiment required a tremendous amount of energy. While it is believed lightning storms were extremely common on the primitive Earth, they were not continuous as the Miller/Urey experiment portrayed. Thus it has been argued that while amino acids and other organic compounds may have been formed, they would not have been formed in the amounts which this experiment produced.

Many of the compounds made in the Miller/Urey experiment are known to exist in outer space. On September 28, 1969, a meteorite fell over Murchison, Australia. While only 100 kilograms were recovered, analysis of the meteorite has shown that it is rich with amino acids. Over 90 amino acids have been identified by researchers to date. Nineteen of these amino acids are found on Earth. (table showing comparison of Murchison meteorite to Miller/Urey experiment) The early Earth is believed to be similar to many of the asteroids and comets still roaming the galaxy. If amino acids are able to survive in outer space under extreme conditions, then this might suggest that amino acids were present when the Earth was formed. More importantly, the Murchison meteorite has demonstrated that the Earth may have acquired some of its amino acids and other organic compounds by planetary infall.

If these compounds were not created in a reducing atmosphere here on Earth as Miller suggested, then where did they come from? New theories have recently been offered as alternative sites for the origin of life.

[319 words]

Continue reading
http://www.chem.duke.edu/~jds/cruise_chem/Exobiology/sites.html


[越障]

NATURE | NEWS FEATURE

Life-changing experiments: The biological Higgs

Biologists ponder what fundamental discoveries might match the excitement of the Higgs boson.

Heidi Ledford
28 March 2012

Biologists may have little cause to envy physicists — they generally enjoy more generous funding, more commercial interest and more popular support. But they could have been forgiven a moment of physics envy last December when, after a week of build-up and speculation, researchers at the Large Hadron Collider (LHC) near Geneva in Switzerland addressed a tense, standing-room-only auditorium.

Scientists there had caught the strongest hints yet of the Higgs boson: what some have called the 'God particle' and the final missing piece of the standard model that explains the behaviour of subatomic particles. The discovery, if confirmed, will mark the culmination of a hunt that has taken years and cost billions of dollars, and will shape the field for years to come. The research community was abuzz. “There were lots of rumours flying around about how significant the signal was,” says Lisa Randall, a theoretical particle physicist at Harvard University in Cambridge, Massachusetts, who got up at 4 a.m. to talk to the press before watching the webcast of the presentation at the LHC. “It's been quite exciting.”

All this led Nature to wonder: what fundamental discoveries in biology might inspire the same thrill? We put the question to experts in various fields. Biology is no stranger to large, international collaborations with lofty goals, they pointed out — the race to sequence the human genome around the turn of the century had scientists riveted. But most biological quests lack the mathematical precision, focus and binary satisfaction of a yes-or-no answer that characterize the pursuit of the Higgs. “Most of what is important is messy, and not given to a moment when you plant a flag and crack the champagne,” says Steven Hyman, a neuroscientist at the Broad Institute in Cambridge, Massachusetts.

Nevertheless, our informal survey shows that the field has no shortage of fundamental questions that could fill an anticipatory auditorium. These questions concern where and how life started — and why it ends.

Is there life elsewhere?

In 1964, palaeontologist George Gaylord Simpson wrote a stinging dismissal of exobiology, the search for life on other planets. “This 'science' has yet to demonstrate that its subject matter exists!” he wrote. The searing critique caused many researchers in the nascent field to shy away from exobiology.

But it was unfair, says planetary scientist Christopher Chyba of Princeton University in New Jersey. Chyba has for years been comparing the search for life on other planets to the search for the Higgs: another quest whose subject has never been proved to exist. “Why should we suddenly become giggly when it is biology at stake, rather than physics?” Chyba wrote in a 2005 rebuttal to Simpson's attack.

The search for extraterrestrial life can be described as one way to test “a standard model of biology”, says astrobiologist Chris McKay of the NASA Ames Research Center in Moffett Field, California. “It's the model of DNA and amino acids and proteins and a genetic code,” he says. “It's the common features of all biology, and the framework through which everything we know about life is based.” If life fundamentally different from this standard model — perhaps relying on a wildly different biochemistry — were found on another planet, it would show that there is more than one way to produce a living system, he adds.

Others say they don't need evidence of such a 'second genesis' to get a Higgs-like thrill from the prospect of life on other planets. “If we found our same biology, but on Mars, that would be pretty exciting,” says biochemist Gerald Joyce of the Scripps Research Institute in La Jolla, California. “Then the question would be: where did it come from first?”

But whereas the Higgs-hunters in Geneva have a good idea of what to look for, astrobiologists seeking alternative forms of life face a bigger logistical challenge: figuring out what clues are most revealing. The chemical signatures of compounds that are commonly associated with life, such as methane or liquid water, could identify planets to focus on. But atmospheric signatures of life are unlikely to be convincing, says Chyba.

Within the Solar System, McKay puts his money on three habitats as most likely to harbour life: Enceladus, an icy moon orbiting Saturn that, according to NASA's Cassini spacecraft, probably has liquid water and is spewing organic material from cracks in its surface3; Mars, but “old Mars, not Mars today”; and Jupiter's moon, Europa, whose icy surface masks tantalizing seas of water. The Mars Science Laboratory, scheduled to land on the red planet in August, will include a simple mass spectrometer and a laser spectrometer, enabling it to detect methane, and could reveal preliminary signs of life. But the mission is not designed to yield definitive evidence.

Another way to hunt for life is to look for organic molecules that are too complex to have arisen by simple chemical synthesis, unaided by enzymes. “Let's say you came to Earth and scooped up matter,” says McKay. “You'd find all of this chlorophyll and DNA: big, huge, complex molecules that were clearly there in high abundance and distinctly different from what you'd expect from a chemical mix.” Finding this would require sophisticated equipment that had been baked and scrubbed free of earthly contaminants and, at present, there are no concrete plans to include such equipment on NASA's proposed trips to Mars or Europa. “My sense is that people are just trying to avoid it as long as possible,” Chyba says. “Money is extremely tight, but at some point we'll just have to bite the bullet.”

Searching rocks on other planets for fossils is another popular proposition, says Jeffrey Bada, a planetary geochemist at the Scripps Institution of Oceanography in La Jolla. “That's easy enough,” he says. “But if you don't find them, does that tell you that life never existed there?” McKay argues that fossil evidence or living proof of life may be required to convince a field. “Ultimately, you'll have to have a body,” he says. “It doesn't have to be alive, but you'll have to have a body.”

Is there foreign life on earth?

Alien life — and a Higgs moment — might also be lurking close to home. Some have postulated the existence of a 'shadow biosphere' on Earth, teeming with life that has gone undiscovered because scientists simply don't know where to look. It could contain life that relies on a fundamentally different biochemistry, using different forms of amino acids or even entirely novel ways of storing, replicating and executing inherited information that do not rely on DNA or proteins.

The idea is not as far-fetched as it might sound, says Steven Benner, a chemist at the Foundation for Applied Molecular Evolution in Gainesville, Florida. Researchers have found shadow biospheres before. The invention of the microscope revealed whole new worlds, says Benner; and the discovery of a new realm of microorganisms, the archaea, opened a window on another. “The question is: is it going to happen again?”

The trick is deciding what to look for and how to detect it. The usual way that researchers search for new organisms — by sequencing DNA or RNA — will not pick up life that does not depend on them.

Some scientists have speculated that desert varnish, a peculiar dark-coloured coating of unknown origin found on many desert rocks, could be a product of a shadow biosphere. Benner suggests looking in nooks and crannies that cannot support conventional life, such as areas with extremely high temperatures, radiation levels or harsh chemical environments.

Felisa Wolfe-Simon, now at the Lawrence Berkeley National Laboratory in Berkeley, California, and her colleagues took this approach when they searched for life in the arsenic-rich environment of California's Mono Lake. In late 2010, they reported the discovery of a life form that can use arsenic in place of phosphorus in its DNA and proteins — a seemingly remarkable departure from conventional life. But at least one attempt to reproduce the result has failed.

Another approach is to search on the basis of size. If cells were liberated from their reliance on bulky ribosomes and proteins, they could be much smaller, says Benner, perhaps tucked away in rocks with pores only nanometres across. That is the rationale behind a project that John Atkins, a molecular geneticist at the University of Utah in Salt Lake City, is pursuing with Richard Herrington of the Natural History Museum in London. They plan to sequence the contents of rocks of different ages and origins with pores less than 100 nanometres in diameter. By screening for nucleic-acid sequences that lack the code for protein-making ribosomes, they hope to find a protein-free life form that has its roots in RNA, as known life probably does, but that arose independently. “The RNA world is thought to have originated, in geological terms, relatively quickly,” Atkins says. “So why couldn't it have arisen again multiple times?”

[1492 words]


Continue reading
http://www.nature.com/news/life-changing-experiments-the-biological-higgs-1.10310
(as attached)

A related TED talk:
John Delano: Is anyone else out there?
https://www.youtube.com/watch?v=qrQY7vQy50M

jiline

早上一来没看到新作业竟然浑身不舒服~~~
1'16 Two situations about exobiology: one people suddently disappeared when you saw a UFO; a juice became a nice bluish-green color with fuzz
1'24 The birth of sun, asteroids, earth(volcanoes, molten rock or lava)
1'42 The birth of water, lakes, oceans, wind. For a long time it was thought the ealy Earth had a reducing atmosphere, but now, most of the scientific community believes the atmosphere was not reducing.
1'46 Scientist conducted experiments to research the origin of life. They found RNA and DNA bases could be obatined through simulated prebiotic chemistry with a reducing atmosphere
2'04 Doubt whether the amino acids were present when the Earth was formed.Questions where did they come from

越障：
8‘23好长呀，记不住全的了，今天的内容好丰富的，还有TED视频
Physicists found the final missing piece of the standard model that explains the behaviour of subatomic particles. But it raises doubts.
1. life else where?
2. alien life on earth?

teddybearj4

占座，姐姐的图图好可爱~
————————————————————
速度：
57"   1'35   1'53   1'15   1'34

越障：10'57
(这篇文章见证了科学就是不断提出问题和解决问题的过程啊~一个问题接着一个问题呀！)
Main idea:
A biologists discusses some questions related to Higgs Boson, which are wait to be studied and solved.
Situation:
In the biology field, it appears a rearch about the Higgs Boson, which catches many interest and appeal lots of funding. In this passage, the author compose the paper by raising some question, then discussing in order to guide the reader's thought.
Problem solving with Q & A:
Q1: Is there life elsewhere?
A:2 ways to explode.
The first is a traditional way? ,but can be improved by Higgs.
Another is organic way, studying fossils,stc.
Q2:Is there foreign life on earth?
A:2 ways to explode.
The first is sequence of DNA,RNA(also a traditional way maybe?).
Another is to search on basis size.
(记科技类文章细节的能力真差唉……基本上是看了后面往前面，看完整篇细节已经基本上都不记得了~)

Olina加油

地板！

0‘49  1’00  1‘05  1’07  1‘08

6’31

zhaobingd

1.21
1.44
2.25
2.17
2.08
第一个是一道蓝光，一个人就消失了，是谁干的呢？
后面的讲地球生物起源的，在模拟元始环境下搞出氨基酸，可以是个很好的证明。
10.56好长啊。
貌似有外星人的事情。宇宙中有其他的生物么？地球上有外星人么？怎么区别呢？

猫咪团团

wow~baby滴~
-----------------------
1:15
1:33
1:23
1:34
1:26

7:49

铁板神猴

<prebiotic earth>'s illustration is so interesting!

铁板神猴

1'00''
1'22''
1'52''
2'03''
1'59''

10'00''

小胖宝

1'29, 2'03, 2'14, 2'15, 1'50, 7'53

暮已央

( ⊙o⊙ )哇~先占位
速度：
1:00；
1:14；
1:36；
1:23；
1:20；
先举了两个例子，假设了两种情况，一种是看见貌似UFO的物体，另一种是许久没回家后发现有奇怪东西，由此引出了外空生物学的概念；
宇宙和太阳的产生→地球及其他行星的产生→地球经历了几大时期的变化，被小行星撞等等；
地球早期大气的构成，产生的化学法英，出现了一些什么物质，产生了降雨冷却地球表面~
最新的研究表明一些化学成分不是反应后产生而是一直存在的；
科学家已经知道了很多，但还有更多未知的等待研究；
M和U做了一个化学实验，在1950年，模拟了地球早期大气成分，得到了氨基酸——这是生命的起源成分之一；后来J做了一个实验，得到了RNA和DNA这些生命产生的重要因素；
这些实验结果令科学家很乐观的认为在几十年间就可以把生命起源之谜破解；实际上，这只是探索的开端；
模拟实验的许多成分在当时的地球存在吗？
有一些成分在造访地球的外空物体——像小行星和彗星——的上面找到了，比如氨基酸，这样的确有可能；
但是如果不是像M实验中的假设呢，那么这些成分又是怎样来的呢？最新的研究提供了一些可能的地方。
越障：8:00
木有看懂···木有看懂···木有看懂···
看到一半就开始走神，各种词汇进了脑子又转了一圈出来了，看的好吃力···
我觉得就算是全部翻译成中文，偶对这个话题还是看不懂···
总之，好像，就是讲了一个关于希格斯玻色子的发现吧（这两个单词还是查出来的）
科学界很振奋，什么化学家要嫉妒物理学家啦···
然后也讨论到了生命起源的事？
外太空有没有生命啦，有的话某人提出可能存在三个星球上面，什么以前的火星，木星的卫星~
再提问，现在的地球上面有外太空生命吗？
然后科学家做了实验，一些什么极端的条件下怎么怎么样，blabla~~~
~\(≧▽≦)/~啦啦啦，我就是没看懂···o(╯□╰)o