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Evidence from meteorites and radioactive isotopes found in the earth’s crust http://universe-review.ca/10-36-Humanevo.jpg Oldest known hominid (artistic portrayal), discovered recently (July 2002) in northern Chad, Africa with a complete cranium and dated back to nearly seven million years ago. Sahelanthropus tchadensis. It is generally believed that humankind had its roots in Africa http://universe-review.ca/I10-36-oldesthominid.jpg http://universe-review.ca/I10-36-familytree.jpg Evolution = Mutation + Natural Selection “Other” Mechanisms: • Mass Extinctions • Cambrian Explosion http://universe-review.ca/I10-70-selection.jpg From the site http://universe-review.ca 30% of the genera wiped out! The suspected causes include severe volcanism and global warming. Plenty of From the site http://universe-review.ca groups, including small predatory dinosaurs, the early mammals, and some crocodile relatives survived into the Jurassic. Yet large groups of archosaurs mysteriously vanished. It really isn't obvious why the non-dinosaurs get hammered the most. Anyway, the end-Triassic extinction pruned a number of dinosaurs, but the group as a whole marched on, and prospered in the Jurassic period. From the site http://universe-review.ca http://universe-review.ca/R10-19-animals.htm Dinosaurs became dominant, reaching their largest size. The brontosaurus (thunder lizard) was a huge sauropod with length up to 80 feet and a total weight of 30 to 35 tons. The large size probably helped them to escape predation by carnivorous dinosaurs. In the same picture, the stegosaur protected itself by the elaborate armour. Its small brain was compensated by large ganglia (a mass of never cells) between the shoulders and another one above the hips; those are sometimes referred to as the second brain. From the site http://universe-review.ca From the site http://universe-review.ca http://universe-review.ca Molecular Clocks Study of DNA variation among different species provides another way to classify them as shown by the tree of life in the figure above. According to this scheme the common ancestor at the base of the tree gave rise to three branches: microbes known as archaea (primitive unicellular organisms that live in most extreme environments), bacteria (unicellular organisms without nucleus or cell structure), and eukaryotes (any organism with one or more cells that have visible nucleus and organelles). The lengths of the branches reflect how much the DNA of each lineage has diverged from their common ancestor. They demonstrate that most of life's genetic diversity turns out to be microbial; the entire animal kingdom (shown at the upper right) are just a few twigs at one end of the tree. http://universe-review.ca http://universe-review.ca 11-cis-retianal trans-retinal rodopsin changes shape makes opsin sticky to transducin GDP from transducin falls off and replaced by GTP activated opsin binds to phosphodiesterase which aqcuires the ability to cut cGMP lower cGMP conc. causes ion channels to close lowering Na concentration in cell and lowers cell potential current transmitted down optic nerve to brain http://universe-review.ca The Cambrian “Explosion” From the site http://universe-review.ca http://universe-review.ca http://universe-review.ca/F10-multicell.htm#animals “There is another and allied difficulty, which is much more serious. I allude to the manner in which species belonging to several of the main divisions of the animal kingdom suddenly appear in the lowest known fossiliferous rocks. Most of the arguments which have convinced me that all the existing species of the same group are descended from a single progenitor, apply with equal force to the earliest known species. For instance, it cannot be doubted that all the Cambrian and Silurian trilobites are descended from some one crustacean, which must have lived long before the Cambrian age, and which probably differed greatly from any known animal. Some of the most ancient animals, as the Nautilus, Lingula, etc., do not differ much from living species; and it cannot on our theory be supposed, that these old species were the progenitors of all the species belonging to the same groups which have subsequently appeared, for they are not in any degree intermediate in character. Consequently, if the theory be true, it is indisputable that before the lowest Cambrian stratum was deposited long periods elapsed, as long as, or probably far longer than, the whole interval from the Cambrian age to the present day; and that during these vast periods the http://universe-review.ca “To the question why we do not find rich fossiliferous deposits belonging to these assumed earliest periods prior to the Cambrian system, I can give no satisfactory answer. Several eminent geologists, with Sir R. Murchison at their head, were until recently convinced that we beheld in the organic remains of the lowest Silurian stratum the first dawn of life. Other highly competent judges, as Lyell and E. Forbes, have disputed this conclusion. We should not forget that only a small portion of the world is known with accuracy….. The several difficulties here discussed, namely, that, though we find in our geological formations many links between the species which now exist and which formerly existed, we do not find infinitely numerous fine transitional forms closely joining them all together. The sudden manner in which several groups of species first appear in our European formations, the almost entire absence, as at present known, of formations rich in fossils beneath the Cambrian strata, are all undoubtedly of the most serious nature…” http://universe-review.ca http://universe-review.ca/R10-19-animals.htm 600 mya rise of Edicarian “fauna”: at various times they have been considered algae, lichens, giant protozoans, or even a separate kingdom of life unrelated to anything living today. A novel explanation suggests that the Ediacaran fossils weren't animals at all. Rather, they were probably lichens. http://universe-review.ca … an artist's impression of the Cambrian scenery at the Burgess Shale halfway up Mt. Field, British Columbia. More than 120 different species of animal fossils have been found there. Some of those shown in the drawing are: sponges, cnidarians, worms, trilobites, anomalocaris, marrella, hallucigenia, sea scorpions, and brachiopods. http://universe-review.ca There is still much controversy over the significance of the Burgess and Chengjiang fossils. What is certain is that the transformation of life from singlecelled organisms to multicellular organisms was swift, sudden and widespread. Another fine bed of early Cambrian fossils exists in Chengjiang, China. This site contains similar type of fossils to those found in the Burgess Shale, and date to around 530 million years old (about 20 million years older than the Burgess Shale fauna). They are the oldest such fossils ever found and contain organisms with soft body parts. Paleontologists have extracted over 100 species of trilobites, worms, sponges and various ancestors of crustaceans, spiders, insects and probable early chordates, as well as numerous problematical forms that cannot definitely be assigned to well established taxa. http://universe-review.ca Unicellular Organisms Research in 2004 attributed the complexity of multicellular organism to the use of RNA based regulatory signals. The Cambrian explosion was related to the abrupt addition of this genetic regulatory system. The figure above shows the complexity of eubacteria and archaea at low levels over the past billion years up to the present. While the complexity in eukaryote organisms advanced gradually up to a ceiling and then increased abruptly at the Cambrian explosion when a new regulatory system became available.. The proliferation of complex life forms some 20 million years prior to the Cambrian explosion might be just the initial trials to become multicellular. http://universe-review.ca