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Four and a half billion years ago, hot gases coalesced into a roiling amalgam of elements that would eventually cool and differentiate into what we now call "Earth."

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For most of scientific history it was believed that the first nascent signs of life did not emerge until one billion years ago, after the Earth had had time to form a cool crust, tepid seas and an oxygenated atmosphere. But evidence now suggests that life emerged billions of years sooner than scientists had believed possible, under conditions once assumed to be  far too hostile to support even the most primitive life.

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Now scientists are looking into the primitive pedigree of a microbe to find the answer to the question that human beings have pondered across the millennia:  How did life emerge and develop on Earth?

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Yellowstone National Park.  For over a century tourists have flocked here to observe its wildlife and it's geothermal spectacles.  The most salient features, of course, are the geysers.  Early trappers and explorers noted how the hot water flowed over patches of brilliant yellow, orange, red and green. Microbiologists, however, would later come to appreciate these natural carpets for more than their riotous colors.

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 The water in these hot springs is hot enough to boil an egg, which, by the way, is illegal, and I brought mine from home to make a point. But what does this have to do with the subject of this unit, you're asking --microbial evolution?  

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Well, quite a lot, actually, because, unlike eggs, certain microbes do not cook in the boiling waters of this hot spring.   In fact, these microorganisms thrive in temperatures that would be lethal to most other forms of life.

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These high temperature-tolerant microbes are called hyperthermophiles. The hyperthermophile's abilities to thrive under such extreme conditions suggest to microbiologists a possible link to the earliest life on Earth, billions of years earlier than scientists had believed it could have existed.

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The main idea behind evolution is the fact that all new species evolve from preexisting ones.  We're going to see how microbes are helping scientists peer back through the mists of time to the very origins of all species. I'm Jim Leinfelder and in this episode of "Unseen Life on Earth, " we'll go back in time and down in size to the beginnings of life.

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For many of us, it's very difficult to accept that we evolved from microbes, from germs. Perhaps one reason is that we, who live on average just 70 years, have such a limited grasp of time -- time like the four and a half billion years the Earth has been around.

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But try thinking of those four and a half billion years being sped up until they all take place in an amount of time we can comprehend -- one 24-hour day.

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 If the history of the Earth were compressed into one day, microbes would be the only form of life on Earth from before sunrise ... until long after sunset. When would the first human beings appear on Earth?  Not until a scant few seconds before midnight.

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German scientist Karl Stetter is returning for the tenth time to the tiny island of Vulcano, off the coast of Sicily. In ancient times, this active volcano was believed to be the gateway to Hades, land of the dead. I love these guys, these volcanos, and there are only two ways -- either you like them or you hate them.

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 I like even the sulfur smell.   So this is an environment which really makes me excited --thinking and dreaming of the primitive Earth.   It's very stimulating for me. At the age of 58, Karl Stetter is focussing his considerable energy on a monumental task -- unraveling the mystery of how life began on Earth.

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But Stetter is not searching for fossils.  He is searching for microbes -- what most of us casually dismiss as germs, but are really tiny fellow residents of the planet, who inhabit a world that is even more complex and diverse than the world we can see.

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 When I was a little child already my parents donated me for Christmas a little my microscope and looked in it.  I saw all this, many shapes of things -- of amoeba and bacteria, and so I became so excited with it, I must work on this.   Now I'm so happy that I even can search for the deep organisms in the tree of life.

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The tree of life.  For thousands of years, human beings have thought of life as being divided into just two branches -- one for plants and one for animals.  

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Now, through breakthroughs in the understanding of DNA, scientists are painting a very different picture of the tree of life. The most amazing discoveries are about the evolutionary relationship between human beings andmicrobes.

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For those of us who think of microbes as germs, it's hard to believe that tiny life-forms like these belong at the beginning of our family tree.

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Yes, that is exactly what Karl Stetter is out to prove.  How?  Just as any one of us might learn more about the history of our own family --by tracking down our oldest living relative. Stetter searches for the hottest spots he can find hoping to locate the modern life-forms that are most closely related to the first life on Earth. 

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 But why hot spots?  From studying microbe fossils, scientists are convinced that life on Earth began before three and a half billion years ago.  But from studying rocks, they've discovered that before three and a half billion years ago, our planet was still steaming hot and covered by oceans that regularly reached the boiling point -- all of which made for a riddle:  What can live in boiling water?

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 Microbes that thrive in boiling water, first extensively studied by Karl Stetter on the island of Vulcano. These amazing microbes live in an environment very much like that of the early Earth.

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Some of these microbes, especially the ones which grow in this high temperature, well, I would say are very different from our way of living.  We are -- for example, we like to have roast pork and, on the other hand, we need oxygen to do our respiration.  And these guys, instead of pork, they like hydrogen gas, and instead of oxygen, they like sulfur. And you see it all here -- yellow --that s a stinky gas of stink bombs. 

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These microbes inhabit such remarkable homes as the boiling mud on the ocean floor near Vulcano. The temperature is about 90 to 95 centigrade, so it's  really damn hot, this sedimen.  Stetter is on a mission to gather another sample of these microbes he affectionately calls "bugs . " He is particularly interested in a species he named "Thermatoga maritima."

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A lot of high temperature bugs are already in and this will be very interesting to look at it in the lab.

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A lot has happened in the intervening billions of years.  Life has evolved from simple single-celled organisms to the myriad diversity of life on Earth.  Nowhere is that diversity more dazzling displayed than in the tropical rain forests that encircle the Earth's equatorial middle.

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Rain forest environments are a nursery for species diversity, accounting for about one/third of all the plants and animals on Earth.  But faced with all that variety, when you  look at the natural world from a genetic perspective, what is perhaps even more astonishing is the profound sameness of all living creatures.  

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By sameness, I mean all organisms contain DNA as genetic material.  All organisms show the same basic steps in genetic information flow. And the biochemical machinery in biological information flow is the same in all organisms.

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All mammals share 97 percent of  all genes.  Three percent is the small  portion that differentiates species  and organisms from each other.  There  are patterns that run through all  living things.  These patterns are  what suggest that all living things  came from the same basic blueprint.

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Macrofossils, such as this fearsome-looking elasmosaur or this? allosaurus behind me here in hot pursuit of a Istegosaurus, can only take us so far back in Earth's history between 140 and 180 million years ago.  Now, as important as large fossils like this are to our understanding of the evolutionary process, they're few and far between and really can only provide an incomplete picture.

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Microfossils, which are rare, give evidence of bacterial life that existed 3.5 billion years ago, but even this evidence won't take us back to the very origins of life.  To get a clearer picture, we need to look further back in time than fossils can take us -- into the DNA, through the prism of living cells.

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 One way to think of DNA is as the re~ for producing a particular kind of organism in the same way that a musical score is the recipe for prying a particular piece of music. In music, hard as it is to believe, the instructions for all the wonderful and complex songs ever written are made up of a finite number of notes.

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In DNA, hard as it is to believe, the instructions for all the wonderful and complex organisms ever produced, including us human beings, are made up of just four different chemicals.

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In music,  this limited number of basic notes have been arranged and rearranged in an almost infinite number of combinations to produce unique scores for all of the songs ever sung.

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In DNA, the basic chemicals have been arranged and rearranged in an almost infinite number of combinations to produce a unique score; what scientists call a "genome" for every organism that has ever existed -- from bacteria to boys. In the 1960s, most scientists  believed that creating a new tree of life by comparing the DNA of different species was impossible.

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But in Urbana,  Illinois, Carl Woese, a jazz aficionado and molecular biologist, disagreed.  For Woese, creating a tree that showed how life on Earth evolved, from the first form of life to the last, became an obsession.

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I knew that this was a jigsaw puzzle that had to be put together.  Now, in my case, I emphasize "had to be," because I understood that to really be a biologist, to really understand biology, you had to understand where everything came from.

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Woese focused first on the evolution of the first forms of life -- microbes.  The problem that had stumped everyone else was that when it comes to microbes, you can't tell much by how closely they're related from just looking at them.

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But Carl Woese had an ace in the hole -- a technique that involved analyzing a unique chain of genetic material that exists inside every living thing -- ribosomal RNA. Woese's technique involved looking at  the essential components of the genetic code.  By breaking the molecules in shorter sections, Woese used radiographic techniques to identify the individual pieces. 

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 Then Woese began the painstaking process of decoding the nucleotides, labeling each either A, C, G, or U, and slowly revealing their sequence.  Why go to such herculean lengths?  Because Woese believed that this chain of nucleotides,  the blueprint for life, could show him how life on Earth evolved. 

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He had learned that this chain has done its job so well that it has been passed down from the first forms of life to all life that followed. Woese realized that by comparing the thousands of A's, C's, G's and U's in the ribosomal RNA chains of two different  species, he would be able to see how much of the score of this special chain they had in common.

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A ribosome's function is to make proteins, regardless of the organism.  Ribosomes equal protein synthesis.  We can safely presume that ribosomes evolved very early, because proteins are the building blocks of all living things.  Ribosomes, themselves, are composed of a number of proteins and various types of RNA.

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What Woese discovered was that the sequence of nucleotides in one of these RNAs varies in different organisms and that the patterns of differences reflects evolutionary change between organisms.  In other words, ribosomal RNA is a document of evolutionary history.

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The more of the score any two species had in con~non, the more closely related Woese believed they had to be on the tree of life.   And it was, indeed, just like putting a jigsaw puzzle together.  You don't know at all what the picture is and then you put all these little islands together and you say,  "0h! Here's a part of it!"

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One key to Woese's approach was to search for the places where major new branches of life began, by looking for the place where a group of A's, C's, G's and U's showed up in an order he'd never seen before.

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 It was like only having heard notes arranged to play classical music your whole life and then suddenly hearing them arranged in a rhythm and blues beat. And slowly, but surely, one after another, the major branchings on the tree began to appear.

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You could feel the thing growing.   The islands became joined, became bigger islands, and then all of a sudden you say,  "Ah!  This is what the picture's going to be about!"  And you gleefully throw in all of the other pieces as fast as you can.

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After more than ten years, Carl Woese completed the puzzle -- a new tree of life created by comparing the ribosomal RNA as an indicator of the genetic makeup of different organisms. When it comes to the branch of the tree that happens to include us human beings, Woese's tree points to a new, very different way of looking at ourselves.

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The new tree is based exclusively on how similar the genetic instructions of different species are,  and the fact is that, just like the scores of country songs are remarkably similar to the scores of rock and roll songs, the scores of plants are stunningly similar to the scores of animals and human beings.

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And so the Woese's tree, far from being just two branches divided between animals and plants, has only allotted animals and plants tiny twigs together, out on the end of the branch we share with all visible life.

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It's difficult to see this tree here as your relative because ever since recorded history, almost, mankind has distinguished between animals and plants.

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 These were the two  great forms of life and they were as different as different could be. But, yet, scientists began to find out that there was a lot of coLL~tonality between plants and us, and that's the thing that has really sort of shocked even me -- to find out not how different animals and plants are, but how much alike they are.

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 If you have a hard time believing that animals and plants are alike, consider what it takes to be different.

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When Woese decoded the scores of a newly discovered group of microbes, including a species that eats volcanic gases in the ocean, he found the letters arranged in a pattern far,  far different than any he'd seen before.   It was as if Woese had discovered a new kind of music that human beings had never heard before.

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Woese found the same unusual pattern in some of the microbes that Karl Stetter had collected from hot springs.

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Woese realized that their unusual genetic material made these strange organisms so different from the bacterial branch and from our branch that they had to be given their own branch on the tree of life, which he named the "archaea," for "ancient."

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Woese's work was especially meaningful to Karl Stetter's work, for it shows that the genetlc progenxtors of all three branches of the tree lived in boiling water.

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Due to the work done by Carl Woese, you can find out where these  little tiny bugs are in the tree of life, and so it was so interesting. The hotter the temperature, the deeper the branches are, and this makes my work even more exciting.

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Our concept of the evolutionary tree has changed over the years.  By studying microbes and examining genetic material, other scientists have created new, more accurate versions of the tree of life model using whole chromosome data.

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This new model is rooted in the comparison of entire genomes, reveal-ing that the genetic relationship of human beings and all the categories of life are linked to each other.

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Now that we have the ability to decipher the entire genetic score of an or------ganism, we are in a position to truly understand the evolutionary relationships between all organisms  and this knowledge will allow us to comprehend the scope of the diversity of microbial life, the subject of the next episode of "Unseen Life on Earth."