contents Principles of Biology page 375 of 989 4 pages left in this module 73 Origin of Life Life on Earth likely began as macromolecules that developed into self-replicating protocells. Lightning during a storm. Scientists hypothesize that forces such as lightning could have provided the energy and circumstances needed for forming complex organic molecules. NOAA Research. Topics Covered in this Module From Organic Molecules to Self-Replicating Protocells How Did Macromolecules Assemble from Organic Molecules? Major Objectives of this Module Explain how organic molecules self-assemble into macromolecules. Describe how macromolecules could replicate using templates. Discuss hypotheses about the formation of self-replicating protocells.
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contentsPrinciples of Biology
page 375 of 989 4 pages left in this module
73 Origin of Life
Life on Earth likely began as macromolecules that developed into self-replicatingprotocells.
Lightning during a storm.Scientists hypothesize that forces such as lightning could have provided the energy and circumstances needed forforming complex organic molecules.NOAA Research.
Topics Covered in this Module From Organic Molecules to Self-Replicating ProtocellsHow Did Macromolecules Assemble from Organic Molecules?
Major Objectives of this Module Explain how organic molecules self-assemble into macromolecules.Describe how macromolecules could replicate using templates.Discuss hypotheses about the formation of self-replicating protocells.
contentsPrinciples of Biology
73 Origin of Life
How did life begin? The short answer is we don't quite know. Evidencecomes from a variety of sources: the anatomy and physiology of current lifeforms and fossils, geologic findings that show how different the Earth wasearlier in its history, data from astronomy describing how stars and planetsare created, and laboratory experiments that attempt to replicate early life ona molecular level. Current hypotheses fit the evidence we have, but becausethe evidence is limited, they are still hypotheses. There is no coherent,widely accepted scientific theory about the origins of life.
From Organic Molecules to Self-Replicating ProtocellsHow are plants and animals different from rocks and water? Livingorganisms reproduce themselves. Even the simplest bacteria produce copiesof their single cells. How could this complicated process have evolved?Scientists generally agree on a basic trajectory. First, organic molecules(molecules containing carbon) developed, then macromolecules, thenprotocells. At what point in this process did the molecules becomeself-replicating, or living?
How did organic molecules originate?Our best interpretation of the scientific evidence available is that a sequenceof events like the following might have occurred: About 4.6 billion years ago,dust and rocks around our Sun condensed to form our solar system,including Earth. The planet would have been battered by rocks and icehurtling through space, keeping it too hot for water to form until conditionscalmed down between 4.2 and 3.9 billion years ago. The atmosphere wasprobably made up primarily of carbon dioxide and nitrogen, but volcaniceruptions might have contributed methane, ammonia, and hydrogen sulfide.As the planet cooled, water vapor in the atmosphere condensed, formingseas. Most of the hydrogen could have escaped into space. Geologicalevidence suggests that almost as soon as the oceans formed, life began.
In the 1920s, two scientists — J. B. S. Haldane, in Britain, and A. I. Oparin,in Russia — independently hypothesized that early Earth might have had areducing atmosphere that, along with energy from ultraviolet radiation orvolcanic explosions, could create organic molecules. A reducing environmentis one that adds electrons to molecules. Haldane called this earlyenvironment a "primitive soup."
In 1953, Stanley Miller, a graduate student working in Harold Urey's lab atthe University of Chicago, tried to replicate the atmospheric conditions ofearly Earth to determine how life could have begun (Figure 1). He simulatedlightning and volcanic eruptions, both conditions that create reducingenvironments. Under the conditions he created, simple chemicals changedinto complex organic molecules, including amino acids (the building blocks ofprotein). Other scientists have replicated these results. One of Miller's formergraduate students, Jeffrey Bada, reanalyzed Miller's original samples in 2008using modern equipment and found additional amino acids Miller had notdetected.
This illustration of the Miller-Urey experiment shows a series of glasstubes and compartments containing water, water vapor, methane, andelectric charge.
Miller and Urey might have produced the wrong atmospheric conditions forreplicating early Earth. More recent evidence suggests that the earlyatmosphere was mostly nitrogen and carbon dioxide, making it closer toneutral: neither electron-adding nor electron-removing. Researchers haverepeated experiments like Miller's with a simulated atmosphere madeprimarily of nitrogen and carbon dioxide, and these researchers have alsofound organic molecules. Based on these findings, a reducing atmospheredoes not appear to be necessary for synthesizing organic molecules.
Another possibility is that life did evolve in a reducing atmosphere but not inthe atmosphere that was typical on most of the planet. How would that havebeen possible? About 30 years ago, geologists discovered hydrothermalvents on the ocean floor. Now many of these vents have been identified, inthe Pacific, Atlantic, Indian, and Arctic Oceans. They arise near volcanoes orwhere tectonic plates are moving apart, in places where the magma beneaththe Earth's crust is exposed, and heat the seawater to temperatures as highas 405°C (761°F). Seawater sinks into the ocean crust, leaches minerals andmetals from the rocks, and then boils up and emerges into the coolerseawater as hot springs. The dissolved material precipitates out, oftencausing what's known as a "black smoker." Hydrogen sulfide and methanecreate a reducing environment. Nearby, temperatures drop dramatically andthe chemical environment changes.
A very hot, acidic environment may sound inhospitable, but many organismslive in or near hydrothermal vents. Archaebacteria in black smokers obtaintheir energy from hydrogen sulfide and replicate at temperatures as high as121°C (250°F), hotter than any other known organism. Thesemicroorganisms are among the most evolutionarily stable organisms known
Figure 2: Unique organisms living in a hydrothermal vent.
Some organisms found in hydrothermal vents might be "living fossils" ofsome of the earliest organisms to evolve on Earth. Panel a): Siboglinidtubeworms (Sclerolinum contortum) spread across the side of a hydrothermalvent in front of white mats of microbes. Panel b): A close-up of thesiboglinid tube worms with small gastropods (Pseudosetia griegi and Skenea
spp.) on the tubes.
(Figure 2). Their presence in hydrothermal vents constitutes one piece ofevidence supporting the idea that life evolved there. Fossilizedmicroorganisms have also been found in fossilized black smokers, includingsulfide deposits dated to over 3 billion years ago. Hydrothermal vents wouldhave existed on earth as soon as water did, around 4.2 billion years ago.Some of the organisms found on hydrothermal vents today, such assiboglinid tubeworms, might be "living fossils," some of the least-changingorganisms to have evolved.
Hydrothermal vents also house bacteria that obtain their energy frommethane. The process that these bacteria use to fix carbon dioxide andproduce ATP, the molecule that provides energy to cells, is similar to thepathway the mitochondria in our own cells use. It is, however, more efficient,producing more energy-containing molecules per cycle. This bacterialprocess might resemble a metabolic pathway that could have sustainedearly-evolving microorganisms.
An alternate theory of how organic molecules arose on Earth is that they didnot form on Earth but simply landed here. A meteorite, called the Murchisonmeteorite, landed in Australia in 1969. It contained more than 70 aminoacids, many in large quantity and some that were unusual. Some of theseamino acids were present in two configurations, called L and D. D and Lisomers are different forms of the same molecule, like mirror images or rightand left hands. While nearly all of the amino acids on Earth are in the Lconfiguration, many of those on the meteorite were in the D configuration.Later research found hints of terrestrial contamination of the meteorite butalso uncovered evidence that at least some of the amino acids and someother molecules had an extraterrestrial origin. The Murchison meteorite alsocontained other organic compounds, including lipids, nitrogenous bases, andsimple sugars, for a count of more than 14,000. Of course, the real answermay be a combination of both theories — it is entirely possible thatmacromolecules both arrived on asteroids and evolved in deep-sea vents.
In 2010, astronomers found something else exciting on an asteroid: ice.Scientists don't know exactly when the current supply of water on Earthdeveloped. One hypothesis is that an extraterrestrial object collided forcefullywith the proto-Earth and began to orbit proto-Earth as our moon. That eventwould have vaporized any water on the planet at the time. Could all of ourwater have been delivered by asteroids?
Figure 3: The asteroid Gaspra, photographed by the Galileospacecraft.
NASA. Figure Detail
One hypothesis about the origin of life holds that ice and organicmolecules came to Earth on asteroids.
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Astronomers once thought the asteroids traveled too close to the Sun tomaintain ice (Figure 3). But then, Andrew Rivkin and Joshua Emery, lookingthrough an infrared telescope at Mauna Kea, Hawaii, found a pattern in theradiation reflecting off an asteroid that indicated ice and organic materials.The astronomers monitored the asteroid, called 24 Themis, over six years.Another team of scientists, led by Humberto Campins, independentlyconfirmed Rivkin and Emery's results. The asteroid 24 Themis is about threetimes further from the Sun than the earth is, but because asteroids have noatmosphere, that distance is usually too close for ice to stay on the surface.Researchers think the ice may be emerging gradually from a reservoir underthe asteroid's surface. Perhaps asteroids brought water to Earth, too, and notjust organic molecules. Of interest, even a planet as close to Sun as Mercurymight, according to recent findings, have pockets of ice in craters at its poles.
The possibility of asteroids bringing the building blocks of life to Earth raisesan intriguing question: if life could happen on Earth, could it also behappening on other planets? After all, we have known since the 17th centurythat our Sun is just one of many Suns within our galaxy. Cosmologists CarlSagan and Stephen Hawking, among other prominent scientists, haveargued that life on Earth is unlikely to be the only life in the universe. Afterall, if it could happen here, why not on another planet with similar conditions?
Test Yourself
What is one explanation for why most isomers of amino acids in living things are those in theL configuration?
Future perspectives and open questions.
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24 Themis might not be representative of asteroids near Earth. It could haveformed much farther from the Sun and later been knocked in closer. Ifasteroids near Earth rarely contain water or organic molecules, it would beless probable that those asteroids played a role in the origin of life. Anotherfactor is the isotope ratio of the ice. If deuterium, or heavy hydrogen (whichcontains an extra neutron and is therefore "heavy"), were found in the sameratio on the asteroid as on Earth, this result would support an asteroid originhypothesis. Julie Castillo-Rogez, an astrophysicist at NASA, has suggestedthat NASA send robotic and manned missions to search for water and ice onasteroids near Earth. Now that researchers have also pretty clearlyestablished the presence of ice and water on Mars, the question ofextreplanetary delivery becomes even more interesting.
Scientists speculate not just about the origin of organic molecules in general,but also about the origins of particular molecules that would have beennecessary at particular stages in the evolution of life. For example, RNAformation requires both ribose and phosphate. Where did these ingredientscome from? Ribose will form from two simple sugars, but it breaks downrapidly in an alkaline, or basic, solution. Alonso Ricardo, a researcher atHarvard University, has studied ways to stabilize ribose. Phosphorus, acritical component of the phosphate backbone connecting ribose moleculesin RNA, is abundant in the Earth's crust but usually isn't released into waterin large quantities, even around modern volcanoes. In 2005, Matthew Pasekand Dante Lauretta at the University of Arizona discovered that solublephosphate is released from certain meteors. The origin of these molecules isa field of active research.
From Organic Molecules toSelf-Replicating Protocells
How Did Macromolecules Assemble fromOrganic Molecules?
Summary
Test Your Knowledge
The Climate Connection
A Sea of Microbes Drives GlobalChange
Stanley Miller Explains
Up Close With Hydrothermal Vents
IN THIS MODULE
WHY DOES THIS TOPIC MATTER?
How is life on Earth reacting toclimate change?
Do floating microbes in the ocean’ssurface waters play an outsize role in globalclimate?
SCIENCE ON THE WEB
Do your own Miller-Urey experiment
Browse through underwater imagescaptured by exploring scientists
contentsPrinciples of Biology
73 Origin of Life
BIOSKILL
BIOSKILL
How Did Macromolecules Assemble from OrganicMolecules?How does a simple, single-celled organism survive and reproduce? It needsmacromolecules like DNA and RNA to make proteins. It needs proteins, suchas enzymes, to make DNA and RNA. How were the first molecules made ifthere were no enzymes? The answer might have been that jack-of-all-tradesmolecule, RNA, or another type of flexible nucleic acid.
Was tPNA the First Genetic Material?Scientists have tried to create self-replicating chains that resemble RNA orDNA, but once bound together, the chains usually do not rearrange theirbase pairs to copy a template. In 2009, the chemist Reza Ghadiri at theScripps Research Institute succeeded in creating a synthetic DNA-likemolecule with nucleic acids reversibly bound to a backbone. They created abackbone from two repeating amino acids, and then attached the bases to itusing adenine thioesters. The molecule is called thioester peptide nucleicacid (tPNA). When put in solution with a DNA template, tPNA rearranges itsnucleic acids to match up with that particular template. Although tPNAdoesn't look like current nucleic acids, the way it works does seem like a steptoward replication. The next step is to find a way to keep the tPNA togetherso it will act as a template for another DNA or PNA strand. PNA is morechemically stable than RNA, and some researchers think that it might havebeen the first genetic material.
Another popular hypothesis is that RNA was the first genetic material.Scientists Thomas Cech and Sidney Altman found that some types of RNAcatalyze reactions, like enzymes. Cech called these RNA catalysts"ribozymes". Ribozymes also produce nucleotide sequences that directlycomplement a piece of RNA, and some ribozymes replicate themselves. Ofthose ribozymes, some replicate themselves faster and with fewer errorsthan others.
David Bartels at the Massachusetts Institute of Technology and AlonsoRicardo and Jack Szostak at Harvard University directed ribozyme evolutionby selecting the most efficient catalysts. After many rounds of selection theyproduced ribozymes that could copy short strands of RNA. Tracey Lincolnand Gerald Joyce at Scripps Research Institute evolved a pair of ribozymesthat could copy each other, but these reactions were catalyzed by complexmacromolecules. Could RNA catalyze its own polymerization? The researchgroup at Harvard tried to make nucleotide polymers form a double strandwithout any catalysts. The reaction took weeks. Then they found that a slightchange to the chemical structure of the sugar component sped up thereaction so that it occurred in only hours. Although this finding could be aclue to the origin of modern-day DNA and RNA, the precise structure of theearliest genetic material remains an open question.
How did self-replicating protocells develop?All cells replicate using DNA in a complicated procedure. The DNA doublehelix unwinds and separates into two strands, and proteins stabilize eachstrand while several enzymes work to create first an RNA primer, then newDNA strands that preserve the information contained in the genome. How,therefore, could a cell replicate without proteins or enzymes?
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Figure 4: Nucleic acid polymerization is catalyzed by clay particles.
Lab experiments have shown that nucleotides are attracted to clayparticles, such as those that may have existed in primordial ponds. Byconcentrating nucleotides in a small area, the clay particles increase therate of nucleotide polymerization, spontaneously forming nucleic acids.Instead of enzymes making a reaction happen more quickly, in this case,clay does the job.
Test Yourself
If some ribozymes do not replicate, some replicate with errors, and some replicate quickly andaccurately, what will happen to the population of ribozymes over time?
Both prokaryotic and eukaryotic cells are enclosed in cell membranes: lipidbilayers with embedded proteins that control what goes in and out of the cell.How could cell membranes have developed? Adding lipids or other organicmolecules to water results in the creation of vesicles, or fluid-filled sacs.Vesicle self-assembly is much more likely when montmorillonite, a type ofclay created by weathering volcanic ash, is added along with organicmolecules to the water (Figure 4). The organic molecules cluster on thesurface of the clay. When positioned close together, they are more likely toform vesicles. The molecules enclosing a vesicle will arrange themselvesinto a bilayer, shielding their hydrophobic ends like the lipid bilayer of a cellmembrane.
Although they are not alive, vesicles have some properties in common withcells (Figure 5). Vesicles can divide to create more vesicles, just as cellmembranes divide to create two cells. They can take in montmorilliteparticles, and if the particles are carrying RNA or other molecules, the
Figure 5: A laboratory-produced protocell that fights cancer.
This electronmicrograph shows a protocell developed in the laboratory forencapsulating and delivering drugs to malignant tumors. Arrows point tothe membrane enclosing the protocell (scale bar = 25 nm).
vesicles will enclose those as well. Vesicles can have an internalenvironment different from the environment outside the lipid bilayer, and theycan grow larger without diluting their contents. Some vesicles can take inmolecules or chemicals selectively and use them in metabolic reactions.
Imagine a vesicle that could grow, split into two vesicles, and carry RNA thatcould replicate accurately and catalyze reactions. Such a vesicle would bealmost like a cell. In fact, vesicles like these could have been protocells thatlater evolved into true cells (Figure 6).
Figure 6: RNA and protocell replication.The first protocell could have formed from the internalization andreplication of nucleic acid molecules inside a phospholipid bilayer.
In the same way that RNA now acts as a template to create proteins, single-stranded RNA might have acted as a template for DNA. Double-strandedDNA is more stable than RNA and is copied more accurately, so cells withdouble-stranded DNA would likely have had an evolutionary advantage. RNAin these cells could have adapted to serve a different function, such astranslating genes into proteins. Protocells might have engulfed other cellsthat later became organelles. Mitochondria, which produce ATP usingglucose and oxygen, and chloroplasts, which produce glucose and oxygenfrom light and carbon dioxide, are widely believed to have begun as differenttypes of bacteria engulfed by host cells, perhaps bacteria much like thosestill living in hydrothermal vents.
Speaking of hydrothermal vents, one way to speed up a reaction — inaddition to enzymes or clay — is to apply heat. How much difference doesheat make? Some reactions that might have been important for developingthe molecules necessary for life on the early Earth are slow at 25°C (77°F).But heating to 100°C (212°F) speeds them up by a factor of 10 million. Of allpossible solvents for the molecules that assembled to create life, hot watermight be the very best. Boiling water is hot enough to speed biochemicalreactions by an enormous rate, but not so hot that it causes most complexmolecules to fall apart. This effect of heat is yet another reason to think lifemight have evolved in volcano vents on the ocean floor, with a reducingenvironment, inorganic nutrients from lava and ash, water, and a largeamount of heat.
Processes that influence the origin of species are not the same as thosethat influence the origin of life.Some people think that evolutionary processes such as natural selection,which is backed by overwhelming evidence and universally accepted as acornerstone of biology, equally explains the origin of life on Earth. It doesn't.Evolution is a characteristic of life, once it exists, but does not explain howlife formed in the first place. As soon as protocells became self-replicating,evolutionary processes such as natural selection and genetic drift wouldhave acted. For example, natural selection would have favored cells thatreplicated more effectively than other cells, cells that could use the availableenergy sources more efficiently, and cells that could repair themselves.
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Evolutionary processes such as natural selection underlie how protocellsevolved into cells, how single-celled organisms evolved into multicellularorganisms, and how organisms diversified into the multitude of species thatwe see across the Earth's ecosystems today. It does not, however, explainhow the ability to self-replicate developed in the first place. Evolutionarytheory deals with the origin of species but not with the origin of life.
Test Yourself
Why doesn't the theory of natural selection apply to the origin of life?
How did life begin? Is there life on other planets? Despite long-standinghuman curiosity about these questions, research on the origin of life hasyielded only a set of hypotheses, not a single accepted theory. Mostscientists agree that organic molecules must have appeared first, thenmacromolecules, and then self-replicating protocells. Maybe life began withmeteorites, or maybe it began in hydrothermal vents, or maybe both. MaybeRNA self-assembly was the first step toward replication, perhaps PNA wasthe first genetic material, or maybe metabolic processes developed first,followed by guided assembly of macromolecules. Chemists, geologists,astronomers, and biologists continue to explore many different ways to testthese hypotheses.
From Organic Molecules toSelf-Replicating Protocells
How Did Macromolecules Assemblefrom Organic Molecules?
Summary
Test Your Knowledge
The Climate Connection
A Sea of Microbes Drives GlobalChange
Stanley Miller Explains
Up Close With Hydrothermal Vents
IN THIS MODULE
WHY DOES THIS TOPIC MATTER?
How is life on Earth reacting toclimate change?
Do floating microbes in the ocean’ssurface waters play an outsize role in globalclimate?
SCIENCE ON THE WEB
Do your own Miller-Urey experiment
Browse through underwater imagescaptured by exploring scientists
contentsPrinciples of Biology
73 Origin of Life
OBJECTIVE Explain how organic molecules self-assemble intomacromolecules.
The origin of the first organic molecules is currently being investigated.These molecules self-assemble in conditions that are likely similar to theenvironment of primitive Earth. Hydrothermal vent conditions are conduciveto the formation of organic molecules. Organic molecules similar to thosefound on Earth are also found on asteroids. Once smaller organic moleculesformed, they might be able to aggregate into larger macromolecules. RNAmight self-assemble and will form relatively long chains in the presence ofclay. This process occurs faster at high temperatures.
OBJECTIVE Describe how macromolecules could replicate usingtemplates.
Some macromolecules, such as RNA, can self-replicate as well as catalyzeother reactions. Both RNA and PNA can produce nucleotide sequences thatare complementary to a strand of nucleic acid without the addition ofenzymes.
OBJECTIVE Discuss hypotheses about the formation of self-replicatingprotocells.
Phospholipids will self-assemble into bilayers when placed in an aqueoussolution. These vesicles can divide, take in macromolecules, and maintain aninternal environment that differs from their external environment. If thesevesicles contain RNA, these protocells might replicate and catalyze reactionswithin their membrane.
protocellA theoretical vesicle that could grow, split into two identical vesicles, and carryRNA that could replicate and catalyze reactions.
Summary
Key Terms
From Organic Molecules toSelf-Replicating Protocells
How Did Macromolecules Assemble fromOrganic Molecules?
Summary
Test Your Knowledge
The Climate Connection
A Sea of Microbes Drives GlobalChange
Stanley Miller Explains
Up Close With Hydrothermal Vents
IN THIS MODULE
WHY DOES THIS TOPIC MATTER?
How is life on Earth reacting toclimate change?
Do floating microbes in the ocean’ssurface waters play an outsize role in globalclimate?
SCIENCE ON THE WEB
Do your own Miller-Urey experiment
Browse through underwater imagescaptured by exploring scientists
page 378 of 989 1 pages left in this module
contentsPrinciples of Biology
73 Origin of Life
1.
The ratio of hydrogen to deuterium didn't match the ratio found on Earth.The meteor could not have accumulated amino acids on Earth because it landedin the ocean.The meteor landed in a barren field where it couldn't have picked up any organicmolecules.They were trapped under a crust and only seeped out when the ice under the crustmelted.About half of the amino acids were D isomers and half were L isomers, whereasnearly all organic molecules on Earth are in the L configuration.
When the Murchison meteorite that landed in Australia was found to contain aminoacids, how could scientists tell they had arrived with the meteorite rather thanhaving contaminated it after it landed?
2.
150 million years ago4.2 billion years ago6,000 years ago90,000 years ago2.2 billion years ago
Approximately when do scientists believe life originated on Earth?
3.
Primitive bacteria can live and reproduce using methane and hydrogen sulfide asenergy sources.RNA molecules will spontaneously self-assemble into polymers on a hot clay orrock surface.Amino acids and other complex organic molecules will spontaneously form in areducing environment.Complex organic molecules will spontaneously form in an atmosphere like that ofearly Earth.Heating water to its boiling point speeds up reactions tremendously, sometimes by10 million-fold.
What did the Urey-Miller experiment show that is still applicable today?
4.
Hydrothermal vents would have been present nearly as soon as Earth wascreated, about 2 billion years ago.On land, volcanic ash creates an environment inhospitable to living organisms.Archaebacteria fix carbon dioxide and produce ATP using the same pathwaymitochondria use.Organisms that live near hydrothermal vents have specific adaptations towithstand these harsh environments.Some of the microorganisms that appear to have evolved earliest still live inhydrothermal vents.
Which piece of evidence supports the idea that life originated in or near submarinehydrothermal vents?
5.
DNA catalyzed the formation of macromolecules.Simple reactions can occur quickly under any circumstances.Heat-catalyzed reactions led to the assembly of macromolecules.
What is the prevailing theory for how macromolecules assembled in the absence ofenzymes?
Test Your Knowledge
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The reactions occurred slowly.Macromolecules catalyzed the formation of more macromolecules.
6.
by cooling the solution to near freezingby adding the ribose sugars to the reaction lastby dissolving them in waterby adding microscopic particles of clayby changing the backbone structure
How have researchers encouraged longer RNA polymers to self-assemble?
7.
Its function changed over time.Its function has remained the same since the origins of life.It evolved after DNA.It evolved after protocells.Its biochemical structure has become completely different since it first originated.
Which of the following statements best represents the most likely evolution ofRNA?
8.
did not play a role in the evolution of early lifeexplains the formation of macromoleculesdetermined the elements available for the evolution of lifedid not play a role in the origins of lifeeliminated meteorite-carrying organisms from Earth
Natural selection ___.
Submit
From Organic Molecules toSelf-Replicating Protocells
How Did Macromolecules Assemble fromOrganic Molecules?
Summary
Test Your Knowledge
The Climate Connection
A Sea of Microbes Drives GlobalChange
Stanley Miller Explains
Up Close With Hydrothermal Vents
IN THIS MODULE
WHY DOES THIS TOPIC MATTER?
How is life on Earth reacting toclimate change?
Do floating microbes in the ocean’ssurface waters play an outsize role in globalclimate?
SCIENCE ON THE WEB
Do your own Miller-Urey experiment
Browse through underwater imagescaptured by exploring scientists
