Theory, Fossils, And A Two-sided Puzzle-t6670

Do fossils support evolution? Or do they undermine the theory? Scientists have now scrutinized over 100,000 specimen from around the world covering fauna from the past 3,500,000,000 years. What have they learned? Let’s check it out. Glimpses from the Past The fossil record has troubles of its own. See if you can follow this logic: Paleontologists start with the premise that evolution progresses from simple to .plex life forms. Thus the simpler the fossil, the older it is. As a result, the fossil is roughly dated according to its .plexity. Paleontologists use the "dated" fossils to establish the age of rock segments in which they are found. Then they turn right around and say, "Look, evolution is a fact. We have a series of increasingly .plex forms taken from chronologically dated rock segments to prove it." The assumption of evolution is used as proof of evolution! The whole thing reminds you of a dog chasing its tail. Just the same, rock layers occasionally play tricks on the experts. More advanced specimen are found in levels lower than expected, while simpler types show up where they shouldn’t be. These contradictions are dismissed as irregularities or nonconformities. But if rock layers are sometimes uncooperative, so are the fossils. Geologists, as well as paleontologists, frequently rely on "index fossils" to provide a rough date for rock segments. That procedure gives us ballpark figures as long as the origin and the extinction dates of the index fossils are known. But what happens when the fossil, which has been officially declared dead millions of years ago, suddenly turns up alive? All the rock segments dated by that fossil have to be reevaluated. This embarrassment has happened all too often. The tuatara lizard, the small mollusk Neopilina galatea, the maidenhair tree, the dawn redwood, and the coelacanth were all thought to be extinct. Now we know better. Have we ironed out all the knotty little dating problems? Probably not, especially when you consider that most index fossils are small marine organisms, and the ocean depths are still largely unexplored. Charles Darwin left us with a pretty good metaphor. He .pared the fossil record to a book in which only a few scattered pages were preserved; on those pages only a few lines are found; of those few lines, just a few words remain; and of those few words, only a few letters are legible. That was a very apt description of the fossil record in Darwin’s day. Our picture of the past is somewhat better than it was in the mid 19th century, but it is still limited. Bear in mind when we find anything at all, it is usually a tooth, bone, or shell – or more likely, just part of a tooth, bone, or shell. Most animals, past and present, have no hard parts. Consequently, we are not likely to find any evidence at all for most species. Occasionally, paleontologists get lucky and find whole specimens preserved intact – soft parts and all. They discover insects in amber or entire .munities of creatures encased in a mud slide. Outside of those rather unusual circumstances, we have little or no evidence of most animals’ soft anatomy. You would think that such a scanty fossil record with all of its limitations and imperfections would be enough to make a paleontologist humble. The fossil record, spotty as it is, still tells us a story we cannot get from any other source. Fossils are our only real evidence of prehistoric life on earth. Over 100,000 specimen from around the world now provide us with a series of glimpses from the past. An imperfect record to be sure, but it’s the best we have. Here is what the fossil record shows: Early Fossils: A Two-Sided Puzzle Precambrian Eon – 3,500,000,000 years ago – Blue-green algae and Bacteria found in 24 locations in western Australia, Africa, and Canada. These were .pletely soft-bodied, single-celled organisms, known as prokaryotes. This is a relatively simple type of cell having no organelles, no nucleus, no paired chromosomes, no mitochondria, and no chloroplasts. They reproduce by simple cell division. The cell divides into two identical "daughter" cells. Since the daughter cells are identical to its "parent," the only way change can .e about is if an accident (mutation) affects the genetic material itself. The difference between prokaryotic cells (blue-green algae, bacteria, and fungi) and eukaryotic cells (all other life forms) is so profound that prokaryotics are classified as a separate kingdom, the kingdom Monera. Precambrian Eon – 1,500,000,000 years ago – Protistans found worldwide. These were .pletely soft-bodied, single-celled organisms, known as eukaryotes. They too have a separate kingdom, called Protista. Some lived by photosynthesis like plants; others fed on food particles like animals; still others did both. Eukaryotes are larger and much more sophisticated cells than the prokaryotes. Outside of bacteria, blue-green algae, and fungi, every other form of life – protistans, plants, and animals – are .posed of eukaryote cells. The difference between the two types of cells is striking. Eukaryote have distinct nucleus with chromosomes containing genetic instructions and a nucleus membrane isolating the genetic material from the rest of the cell. Moreover, eukaryotic cells include a nucleolus which synthesizes ribosomes: endoplasmic reticulum which transports materials and synthesizes lipids and certain proteins; golgi .plex which stores materials and transports them out of the cell and synthesizes carbohydrates; lysomes which break down unwanted molecules; and mitochondri which performs cellular respiration. What does all of this mean? It means after two billion years of nothing but prokaryotes, we run into an entirely different form of life. Cell by cell you, I, and an oak tree have more in .mon with a single-celled protistan than the protistan has in .mon with a bacteria or blue-green algae. It’s a big leap from a prokaryote to an eukaryote. And there is nothing between. Think of two billion years of seeing nothing but three-piece jazz bands. Suddenly, you encounter a full symphony orchestra. If your theory was that jazz bands evolved into symphony orchestras, you would expect to find a few intermediate-sized bands between the two. The puzzle remains. If prokaryotes evolved into eukaryotes, why don’t we see a progression of forms? Some reason that since the intermediate forms would be soft bodied, we shouldn’t expect to find any fossilized remains. The obvious reply to this argument is: All the prokaryotes and the protistans were soft bodied too. Yet we have discovered a good number of each intact, whole, and clearly distinguishable from each other. However, we find no transitional cells between the two. Life in the fossil record is 3.5 billion years old. For 2.8 billion years – 80 percent of life’s fossil history – life apparently did not evolve at all. It stayed on the same level of single-celled organisms, each one carrying on all life’s functions independently. Then around 700 million years ago, multicellular animals began showing up in the fossil record. Precambrian Eon – 700,000,000 years ago – Ediacara fauna found worldwide. Ediacara fauna are the first known multicellular animals. These large pancake-flat soft bodied creatures were originally discovered in Australia but the fauna has since been found world wide. They may have been an experiment in multicellular life that failed. Their design matches no modern anatomical plan. By the Cambrian period, all traces of these animals had perished. Cambrian Period – 525,000,000 years ago – Anemones, Clams, Crustaceans, Jelly Fish, Octopuses, Sea Lilies, Snails, Sponges, Starfish, Trilobites, and Worms. By the end: Corals and Chordates – found worldwide. Paleontologists call it the Cambrian explosion. In a geological moment just before the beginning of the Cambrian, nearly all modern invertebrate phyla appear suddenly and simultaneously along with an even greater number of anatomical curiosities which did not survive. Phylum already show their distinct characteristics. Transitional forms are conspicuously absent. Even classes, the taxonomic level below phylum are found in place and very similar to what they are today. At the lowest classification level, more than five thousand species have been discovered in the Cambrian layers. Surprising? Yes, it is. Evolution is not suppose to work that way. In a geological blink of an eye, we go from single-celled organisms to a vast array of .plete, multi-celled animals found worldwide. These animals are fully equipped with intestines, hearts, stomachs, bristles, eyes, and feelers. The eyes and feelers tell us that .plex nervous systems were already intact. Trilobites show a distinctive head and tail, numerous thoracia parts, joint legs, a .plex respiratory system, and fully developed .pound eyes. The relatively simple single-celled prokaryote dates back 3.5 billion years; 2,975,000 years later we find the highly .plex, multi-celled, multi-organed trilobite. For all practical purposes, everything between the two is a missing link. Did a prokaryote cell evolve into an eukaryote cell? Did an eukaryote cell in turn evolve into the trilobite, sponge, jellyfish etc., of the Cambrian period? The fossil record is .pletely silent on these subjects. What we find is a two-sided puzzle. We have explored the first half of that puzzle. Life didn’t evolve. It stayed at the same level of single cells for 2,800 million years. Then after one or possibly two false starts, life exploded into a multitude of radically different, .plex creatures. Equally inexplicable is the flip side of the coin. Over five hundred million years have passed since the end of the Cambrian period, and not a single new animal phylum or basic design has shown up in the fossil record. Something opened the flood gates 525 million years ago, and out poured phyla and classes. The gates remained open for five to ten million years. Then abruptly, they were closed again. Few new classes and no new phylum have appeared since that time. The last 500 million years have added nothing but variations to the well-established Cambrian designs. Most curious. One explanation for the Cambrian explosion is that the period merely marks the appearance of shells in the fossil record. Before developing shells, multicellular life may have undergone a long history of gradually increasing .plexity, leaving no record in the rocks. If you will recall, that’s the pretext offered for not finding intermediate stages between prokaryote and eukaryote cells. That line of reasoning ignores all of the soft-bodies fauna gathered from rock segments dated before, during, and after this period. In fact, soft bodies were the rule – not the exception in the early years of life. Bacteria, blue-green algae, the protistans, and the Ediacara fauna were all soft-bodied types. Even the creatures in the Burgess Shale were partially soft. Yet we find a number of them preserved intact. All of these soft forms defied the odds and found their way into the fossil record. Bearing all of that in mind, let’s assume for a moment that the theory of evolution is correct. If single-celled eukaryotes took million and millions of years to evolve into jellyfish, trilobites, octopuses, and all of the other five thousand species of the Cambrian period, why haven’t any of those intermediate fossils turned up? And another question: Why did all the Cambrian fossils, diverse as they are, choose the same geological moment for developing shells? Here is one possible explanation. No Cambrian fauna predecessors have been found because — there weren’t any. And those shelled fossils all appeared at the same time because that is when those animals came into existence. This interpretation accounts for all the known facts. Moreover, it does not resort to any slight of hand, claiming that all the important evidence is for one reason or another "off the record." 相关的主题文章: