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The History of Life Unit 5 Chapter 14 Hypothesis of early Earth Very hot surface from colliding meteorites Very hot planet core from radioactive materials Volcanoes spewing lava and gases that helped to form the early atmosphere Hypothesis of early Earth About 4.4 billion years ago, Earth might have cooled enough for the water in its atmosphere to condense. This might have led to millions of years of rainstorms with lightning, enough rain to fill depressions that became Earth’s oceans. The oldest rocks dated are 3.9 million years old. Fossils: evidence of an organism that lived long ago that is preserved in Earth’s rocks Paleontologists estimate that about 95% species are extinct from life’s origins. Climate and ancient geography can be determined from fossils. Types of Fossils Formation Fossils Types A trace fossil is any indirect A trace fossil is anyevidence indirect evidence Trace fossils left by an animal and may include a footprint, a trail, or a burrow. When minerals in rocks fill a space left by a decayed organism, they make a replica, or cast, of the organism. Casts Molds A mold forms when an organism is A mold forms when an organism is Petrified/ Permineralized fossils AmberPreserved or frozen fossils buried in sediment and then decays, leaving an empty space. Petrified-minerals sometimes penetrate and replace the hard parts of an organism. Permineralized-void spaces in original organism infilled by minerals. At times, an entire organism was quickly trapped in ice or tree sap that hardened into amber. Forming fossils Organisms usually have to be buried in mud, sand, or clay soon after they die. It is not likely that each species that ever existed will be fossilized. Most fossils are found in sedimentary rocks. Relative dating If the rock layers have not been disturbed, the layers at the surface must be younger than the deeper layers. Using this principle, scientists can determine relative age and the order of appearance of the species that are preserved as fossils in the layers. Radiometric dating Determines specific age of rocks Radioactive isotopes are atoms with unstable nuclei that break down, or decay, over time, giving off radiation. Because every radioactive isotope has a characteristic decay rate, scientists use the rate of decay as a type of clock. The decay rate of a radioactive isotope is called its half-life. Half-life Geological time scale divided into four large sections the Precambrian Era the Paleozoic Era the Mesozoic Era and the Cenozoic Era Each era is subdivided into periods. What has been learned from fossils several episodes of mass extinction that fall between time divisions mass extinction: an event that occurs when many organisms disappear from the fossil record almost at once The geologic time scale begins with the formation of Earth about 4.6 billion years ago. Precambrian – 87% of history Oldest fossils about 3.4 billion years old resembling cyanobacteria stromatolites. Stromatolites still form today in Australia from mats of cyanobacteria. The stromatolites are evidence of the existence of photosynthetic organisms on Earth during the Precambrian. Only prokaryotic life found in fossil record End of Precambrian – 543 MYA multicellular eukaryotes, such as sponges and jelly-fishes, diversified and filled the oceans Paleozoic and Cambrian Period Paleozoic Era: more animals and plants Early: fishes, aquatic vertebrates, ferns Middle: amphibians Late: reptiles and mass extinction Cambrian Period: oceans teemed with many types of animals, including worms, sea stars, and unusual arthropods Mesozoic - 248 MYA Triassic Period: mammals and dinosaurs Jurassic Period: dinosaurs and birds Cretaceous Period: more mammals, flowering plants, but mass extinction of dinosaurs 65 MYA Continental drift Earth’s continents have moved during Earth’s history and are still moving today at a rate of about six centimeters per year. The theory for how the continents move is called plate tectonics. Changes during the Mesozoic Era Click on image to play video. Cenozoic – 65 MYA It is the era in which we now live. Mammals began to flourish during the early part of this era. Primates diversified 75 MYA. Early ideas about origin of life spontaneous generation: nonliving material can produce life Redi disproved this idea in 1668. Pasteur also disproved this idea in the 1800s. He solidified that idea that life begets life. Scientific hypotheses of life’s origins First, simple organic molecules, or molecules that contain carbon, must have formed. Then these molecules must have become organized into complex organic molecules such as proteins, carbohydrates, and nucleic acids that are essential to life. Oparin experiment: energy from the sun, lightning, and Earth’s heat triggered chemical reactions to produce small organic molecules from the substances present in the atmosphere Primordial soup Rain probably washed the molecules into the oceans to form what is often called a primordial soup In 1953, two American scientists, Stanley Miller and Harold Urey, tested Oparin’s hypothesis by simulating the conditions of early Earth in the laboratory. Protocell Protocell: membranous structures capable of growth and reproduction The work of American biochemist Sidney Fox in 1992 showed how the first cells may have occurred. Likely the first cells were anaerobic, unable to use oxygen and able to use organic materials in the oceans as energy. Archaebacteria Prokaryotic Live in harsh environments, such as deep-sea vents and hot springs Used sulfur as energy to make glucose (sugar) Photosynthetic bacteria Photosynthesizing prokaryotes might have evolved next, releasing oxygen. Oxygen in Earth’s atmosphere increased to form a protective ozone layer. Organisms that use oxygen to make ATP energy molecules through aerobic respiration evolved. The earliest photosynthetic cells – 3.4 MYO and resembling archaebacteria Endosymbiotic theory American biologist Lynn Margulis in the early 1960s proposed this theory. This explains how eukaryotic cells may have evolved. Evidence: Mitochondria and chloroplast organelles have circular DNA like bacteria. They reproduce independently of the cell. They are the same size as bacteria. Endosymbiotic theory A prokaryote ingested some aerobic bacteria. The aerobes were protected and produced energy for the prokaryote. Aerobic bacteria Over a long time, the aerobes become mitochondria, no longer able to live on their own. Mitochondria Some primitive prokaryotes also ingested cyanobacteria, which contain photosynthetic pigments. Cyanobacteria The cyanobacteria become chloroplasts, no longer able to live on their own. Chloroplasts Plant cell Prokaryote Animal Cell