The Origin of Life

"On this single planet called Earth, there co-exist (among countless other life forms), algae, beetles, sponges, jellyfish, snakes, condors, and giant sequoias. Imagine these seven living organisms lined up next to each other in one-place. If you didn't know better, you would be hard-pressed to believe that they all came from the same universe, much less the same planet."
-- Neil deGrasse Tyson

Neil De Grasse Tyson is Frederick P. Rose Director, Hayden Planetarium, American Museum of Natural History (since 1996); Visiting Research Scientist, Department of Astrophysics, Princeton University (since 1994). He writes a monthly column called "Universe" for Natural History magazine and is the author of several books, including "One Universe: At Home in the Cosmos" (2000) and "The Sky is Not the Limit: Adventures in an Urban Environment" (2000).

His most recent work is the book (published by W.W. Norton & Co.) and NOVA PBS four-part series, "Origins". Chapter fifteen, titled "The Origin of Life on Earth," is excerpted here with publisher permission.

The search for life in the universe begins with a deep question: what is life? Astrobiologists will tell you honestly that this question has no simple or generally accepted answer.

Not much use to say that we'll know it when we see it. No matter what characteristic we specify to separate living from nonliving matter on Earth, we can always find an example that blurs or erases this distinction. Some or all living creatures grow, move, or decay, but so too do objects that we would never call alive.

Does life reproduce itself? So does fire. Does life evolve to produce new forms? So do certain crystals that grow in watery solutions. We can certainly say that you can tell some forms of life when you see them -- who could fail to see life in a salmon or an eagle?-- but anyone familiar with life in its diverse forms on Earth will admit many creatures will remain entirely undetected until the luck of time and the skill of an expert reveal their living nature.

Since life is short, we must press onward with a rough-and-ready, generally appropriate criterion for life. Here it is: Life consists of sets of objects that can both reproduce and evolve. We shall not call a group of objects alive simply because they make more of themselves. To qualify as life, they must also evolve into new forms as time passes.

This definition therefore eliminates the possibility that any single object can be judged to be alive. Instead, we must examine a range of objects in space and follow them through time. This definition of life may yet prove too restrictive, but for now we shall employ it.

As biologists have examined different types of life on our planet, they have discovered a general property of Earthlife. The matter within every living Earth creature mainly consists of just four chemical elements: hydrogen, oxygen, carbon, and nitrogen.

All the other elements together contribute less than one percent of the mass of any living organism. The elements beyond the big four include small amounts of phosphorus, which ranks as the most important, and is essential to most forms of life, together with still smaller amounts of sulfur, sodium, magnesium, chlorine, potassium, calcium, and iron.

But can we conclude that this elemental property of life on Earth must likewise describe other forms of life in the cosmos? Here we can apply the Copernican principle in full vigor. The four elements that form the bulk of life on Earth all appear on the short list of the universe's six most abundant elements. Since the other two elements on the list, helium and neon, almost never combine with anything else, life on Earth consists of the most abundant and chemically active ingredients in the cosmos.

Of all the predictions that we can make about life on other worlds, the surest seems to be that their life will be made of elements nearly the same as those used by life on Earth. If life on our planet consisted primarily of four extremely rare elements in the cosmos, such as niobium, bismuth, gallium, and plutonium, we would have an excellent reason to suspect we represent something special in the universe. Instead, the chemical composition of life on our planet inclines us toward an optimistic view of life's possibilities beyond Earth.

The composition of life on Earth fits the Copernican principle even more than one might initially suspect. If we lived on a planet made primarily of hydrogen, oxygen, carbon, and nitrogen, then the fact that life consists primarily of these four elements would hardly surprise us. But Earth is mainly made of oxygen, iron, silicon, aluminum, and iron. Only one of these elements, oxygen, appears on the list of life's most abundant elements.

When we look into Earth's oceans, which are almost entirely hydrogen and oxygen, it is surprising that life lists carbon and nitrogen among its most abundant elements, rather than chlorine, sodium, sulfur, calcium, or potassium, which are the most common elements dissolved in seawater. The distribution of the elements in life on Earth resembles the composition of the stars far more than that of Earth itself. As a result, life's elements are more cosmically abundant than Earth's-- a good start for those who hope to find life in a host of situations.

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Just a good reminder about one of the biggest question, I guess. What is life?

I was always thinking that life while in some aspects unique, also is an integral part of the universe (like stars, planets and galaxies) - i.e. must have evolved somewhere else other than Earth.

I think there are two different realms we deal with, ie, physical and spiritual, and "life" is kind of the interaction between the two. I don't know if that makes sense to anybody.

Sometimes I think that the divisions we make do not exist anywhere else, but our minds. Sure, we all understand physical and spiritual (and the differences), but don't forget that spiritual still is connected with physical (your neurons are made of atoms)....

It's just sometimes hard for me to draw the line separating life from no-life (as it is for scientists apparently).

This has nothing to do with the original post. But Ender I like your little snail, it reminds me of the one I have.

--PunkDavid

In an aquarium.

about what life is, and what made the elements combine into life, i remember that episode of Cosmos, when Carl Sagan mixes the chemical elements and submits the mixture to pressure and heat and, of course knowing from the beginning it would not work, makes the viewers conclude that science has been learning to break things into smaller and smaller pieces, but hasn't come to the point of unveiling the greater hows and whys of creation. i've said that before, i believe that science is following the rusted signs paved by spirituality. subatomic space is alike intergalactic space, mathematical harmony in the physical world… the deeper you go in matter, and the further you go in space, rules bend, boundaries get thinner. it's the realm of mystery. maybe science and spirituality will bind again, the way it used to be in the beginning, and solve the mystery together. IMO.

There's something to it, isn't it? Cause sometimes the more precisely you try to define something (like life), the more you see it can't be done and the definition escapes you, because at a certain level things tend to blend into each other.

Physicists believe that all the basic forces found in nature (the electromagnetic force, the weak and strong nuclear forces, and gravity) all come from the same force (i.e. they were one force shortly after Big Bang). Now they all have different properties and 'look' different, but still are in a way the same thing.

I think it's a bit like that with the living and non-living parts of our universe.

What is life?

Duh.

Life is something that breathes, eats and grows. Didn't you see that episode of Sesame Street? The shoe did not eat the food when Robin Williams put the food in it because the shoe was not alive.

http://www.foxnews.com/story/0,2933,367260,00.html

Study: Life's Raw Material Came from Space

We may all be aliens, it seems. Some of the building blocks of life on Earth came from space, according to a new study of molecules in meteorite fragments.

The study confirmed that some of the raw material for DNA and RNA found in a meteorite did not contaminate the rock after it landed on Earth, but actually originated in space.

The materials in question are the molecules uracil and xanthine, which are precursors to the compounds that make up DNA and RNA, and are known as nucleobases.

"We believe early life may have adopted nucleobases from meteoritic fragments for use in genetic coding which enabled them to pass on their successful features to subsequent generations," said the study's lead author, Zita Martins, a researcher in the Department of Earth Science and Engineering at Imperial College London.

Martins and her colleagues detailed their findings in the June 15 issue of the journal Earth and Planetary Science Letters.

The team discovered the molecules in rock fragments of the Murchison meteorite, which crashed in Australia in 1969.

The scientists analyzed the genetic building blocks and found that they contain a heavy form of carbon which could only have been formed in space. Materials formed on Earth are made of a lighter type of carbon.

The two molecules in this study are only a few of the organic molecules that have been detected in the famous Murchison meteorite, said David Deamer, a chemist at the University of California, Santa Cruz.

"There are about 70 different amino acids in the Murchison meteorite," Deamer told SPACE.com. "About six or so are the same kinds of amino acids associated with life on Earth."

Uracil is one of the four base molecules of RNA, so is vital for life.

Just because the molecules found on this meteorite and others came from space doesn't mean that the same compounds weren't also independently synthesized on Earth, Deamer pointed out.

Scientists are unsure how many of the building blocks of life on Earth originated on this planet, and how many came from beyond.

"We don't know the answer yet," he said. "Most people would say that both contributed to the organic compounds available on Earth, but we don't know with certainty how much of one compared to the other."

Many space rocks similar to the Murchison meteorite rained down on Earth between 3.8 and 4.5 billion years ago, when primitive life was forming. The heavy bombardment would have dropped large amounts of meteorite material to the surface on planets such as Earth and Mars.

Martins and her colleagues say their discovery may help shed light on how life first evolved in our solar system.

"Because meteorites represent leftover materials from the formation of the solar system, the key components for life — including nucleobases — could be widespread in the cosmos," said co-author Mark Sephton, a professor of Earth science and engineering at Imperial College London. "As more and more of life's raw materials are discovered in objects from space, the possibility of life springing forth wherever the right chemistry is present becomes more likely."

So a machine that is sophisticated enough to breathe, eat and grow is alive?

Have you found one that does? I can see teaching it to "breathe" and "eat". But to re-create itself on a cellular level in order to attain more mass and really truly grow? Hmmm. I think that'd be neato!!!


Why is it news that "Life's raw materials came from space" ?? Are we soooooo arrogant now that we believe the Earth to be independent from the rest of the universe??

wait, you know god sent along that meteorite, right?

For me, life is when molecules act in a apparently way of reproducing a pattern...for example, i consider viruses to be alive. If they are not alive, they musr be the most complex poison ever.

http://www.nytimes.com/2009/05/14/science/14rna.html?em

Chemist Shows How RNA Can Be the Starting Point for Life

An English chemist has found the hidden gateway to the RNA world, the chemical milieu from which the first forms of life are thought to have emerged on earth some 3.8 billion years ago.

He has solved a problem that for 20 years has thwarted researchers trying to understand the origin of life — how the building blocks of RNA, called nucleotides, could have spontaneously assembled themselves in the conditions of the primitive earth. The discovery, if correct, should set researchers on the right track to solving many other mysteries about the origin of life. It will also mean that for the first time a plausible explanation exists for how an information-carrying biological molecule could have emerged through natural processes from chemicals on the primitive earth.

The author, John D. Sutherland, a chemist at the University of Manchester, likened his work to a crossword puzzle in which doing the first clues makes the others easier. “Whether we’ve done one across is an open question,” he said. “Our worry is that it may not be right.”

Other researchers say they believe he has made a major advance in prebiotic chemistry, the study of the natural chemical reactions that preceded the first living cells. “It is precisely because this work opens up so many new directions for research that it will stand for years as one of the great advances in prebiotic chemistry,” Jack Szostak of the Massachusetts General Hospital wrote in a commentary in Nature, where the work is being published on Thursday.

Scientists have long suspected that the first forms of life carried their biological information not in DNA but in RNA, its close chemical cousin. Though DNA is better known because of its storage of genetic information, RNA performs many of the trickiest operations in living cells. RNA seems to have delegated the chore of data storage to the chemically more stable DNA eons ago. If the first forms of life were based on RNA, then the issue is to explain how the first RNA molecules were formed.

For more than 20 years researchers have been working on this problem. The building blocks of RNA, known as nucleotides, each consist of a chemical base, a sugar molecule called ribose and a phosphate group. Chemists quickly found plausible natural ways for each of these constituents to form from natural chemicals. But there was no natural way for them all to join together.

The spontaneous appearance of such nucleotides on the primitive earth “would have been a near miracle,” two leading researchers, Gerald Joyce and Leslie Orgel, wrote in 1999. Others were so despairing that they believed some other molecule must have preceded RNA and started looking for a pre-RNA world.

The miracle seems now to have been explained. In the article in Nature, Dr. Sutherland and his colleagues Matthew W. Powner and Béatrice Gerland report that they have taken the same starting chemicals used by others but have caused them to react in a different order and in different combinations than in previous experiments. they discovered their recipe, which is far from intuitive, after 10 years of working through every possible combination of starting chemicals.

Instead of making the starting chemicals form a sugar and a base, they mixed them in a different order, in which the chemicals naturally formed a compound that is half-sugar and half-base. When another half-sugar and half-base are added, the RNA nucleotide called ribocytidine phosphate emerges.

A second nucleotide is created if ultraviolet light is shined on the mixture. Dr. Sutherland said he had not yet found natural ways to generate the other two types of nucleotides found in RNA molecules, but synthesis of the first two was thought to be harder to achieve.

If all four nucleotides formed naturally, they would zip together easily to form an RNA molecule with a backbone of alternating sugar and phosphate groups. The bases attached to the sugar constitute a four-letter alphabet in which biological information can be represented.

“My assumption is that we are here on this planet as a fundamental consequence of organic chemistry,” Dr. Sutherland said. “So it must be chemistry that wants to work.”

The reactions he has described look convincing to most other chemists. “The chemistry is very robust — all the yields are good and the chemistry is simple,” said Dr. Joyce, an expert on the chemical origin of life at the Scripps Research Institute in La Jolla, Calif.

In Dr. Sutherland’s reconstruction, phosphate plays a critical role not only as an ingredient but also as a catalyst and in regulating acidity. Dr. Joyce said he was so impressed by the role of phosphate that “this makes me think of myself not as a carbon-based life form but as a phosphate-based life form.”

Dr. Sutherland’s proposal has not convinced everyone. Dr. Robert Shapiro, a chemist at New York University, said the recipe “definitely does not meet my criteria for a plausible pathway to the RNA world.” He said that cyano-acetylene, one of Dr. Sutherland’s assumed starting materials, is quickly destroyed by other chemicals and its appearance in pure form on the early earth “could be considered a fantasy.”

Dr. Sutherland replied that the chemical is consumed fastest in the reaction he proposes, and that since it has been detected on Titan there is no reason it should not have been present on the early earth.

If Dr. Sutherland’s proposal is correct it will set conditions that should help solve the many other problems in reconstructing the origin of life. Darwin, in a famous letter of 1871 to the botanist Joseph Hooker, surmised that life began “in some warm little pond, with all sorts of ammonia and phosphoric salts.” But the warm little pond has given way in recent years to the belief that life began in some exotic environment like the fissures of a volcano or in the deep sea vents that line the ocean floor.

Dr. Sutherland’s report supports Darwin. His proposed chemical reaction take place at moderate temperatures, though one goes best at 60 degrees Celsius. “It’s consistent with a warm pond evaporating as the sun comes out,” he said. His scenario would rule out deep sea vents as the place where life originated because it requires ultraviolet light.

A serious puzzle about the nature of life is that most of its molecules are right-handed or left-handed, whereas in nature mixtures of both forms exist. Dr. Joyce said he had hoped an explanation for the one-handedness of biological molecules would emerge from prebiotic chemistry, but Dr. Sutherland’s reactions do not supply any such explanation. One is certainly required because of what is known to chemists as “original syn,” referring to a chemical operation that can affect a molecule’s handedness.

Dr. Sutherland said he was working on this problem and on others, including how to enclose the primitive RNA molecules in some kind of membrane as the precursor to the first living cell.

it was the /size that had me convinced.

I thought God did it 6000 years ago

heretics

i respect your opinion but i disagree.

CAN YOU EXPLAIN THE COMPLEXITY OF THE EYE OH I DON'T THINK SO!!! Therefore, God exists. Pwnd.

interesting stuff