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THE HISTORY OF LIFE Ch 14 EARTH’S EARLY HISTORY Evolution is a scientific THEORY based on different types of evidence collected over the years Evidence Includes: Earth was an inhospitable planet Hot Volcanic gasses First organisms appeared between 3.5 to 3.9 billion years ago There is direct evidence of Earth’s history Fossils & rocks show that Earth formed about 3.9 billion years ago HISTORY IN ROCKS Fossils = any evidence of an organism that lived long ago Trace fossils – something left by an animal (example footprint, trail, burrow) Casts – minerals in rocks fill a space left by a decayed organism (form a replica of organism) Petrified fossils – minerals replace the hard parts of an organism Imprints – thin objects can leave an imprint as sediments turn to rocks Amber-preserved & frozen – actual organism is trapped in amber or ice Dunkleosteus (30 ft long; bony skull shown here is about 1 meter high) Extinct at the end of the Devonian FOSSIL EXAMPLES STUDYING FOSSILS Paleontologists study fossils Kinds of organisms that lived Learn about behavior Earth’s climate Geography (rivers, continent position) Fossils are found in sedimentary rock Organism is buried in mud, sand, or clay soon after death Particles compress & harden over time to form sedimentary rock DETERMINING FOSSIL AGE Relative dating Surface layers are newest so they have the most recent fossils. Deeper layers contain older fossils Scientists can determine the order of appearance & extinction Radiometric dating Uses radioactive isotopes Potassium 40 (half life of 1.3 billion yrs) Carbon 14 (half life of 5730 years) Scientists can approximate ages THE GEOLOGIC TIME SCALE A time scale of Earth’s existence based on fossil evidence 4.6 billion years ago – present Divided into Eras Precambrian, Paleozoic, Mesozoic, Cenozoic Distinguished by organisms that lived during the era Eras are divided into periods Mass extinction = entire groups of organisms disappear from the fossil record almost all at once PRECAMBRIAN ERA 87% of Earth’s history 3.5 billion years ago to 544 million years ago Began with prokaryotes Eukaryotes developed and flourished Soft-bodied invertebrates (jellyfish, sponges) Oldest fossils – 3.5 billion years old resemble forms of modern species of cyanobacteria Stromatolites – evidence of photosynthetic bacteria PALEOZOIC ERA Beginning (Cambrian period) Dramatic increase in diversity of life forms Worms, sea stars, trilobites in the oceans Fish appeared – oldest animals with backbones Land species – ferns & seed plants Middle – amphibians End – Reptiles Largest mass extinction – 90% of Earth’s marine species & 70% of the land species disappeared MESOZOIC ERA Began about 245 million yrs ago Triassic Jurassic (began ~ 280 million years ago) Mammals appeared on Earth Early mammals were small and mouselike Age of the Dinosaurs Birds appeared Evidence of bird relation to dinosaurs Cretaceous (began ~ 144 million years ago) New types of mammals & flowering plants Mass extinction of dinosaurs ~ 66 million years ago GEOLOGICAL EVENTS OF THE MESOZOIC Geologic evidence of a large crater East of Mexico Continental Drift Could have filled the atmosphere with dust, changing climate Pangaea broke apart & continents began to move apart Plate tectonics = Earth’s crust consists of several rigid plates on top of molten rock. Plates continuously move Explains continental drift CENOZOIC ERA Began ~ 66 million years ago – the current era Mammals began to flourish Primates appeared (~30 million years ago) Modern humans appeared (~200,000 yrs ago) 14.2 ORIGIN OF LIFE THE ORIGIN OF LIFE ON EARTH Abiogenesis – life from non-living things and Spontaneous Generation = idea that nonliving material can produce life Primordial Soup – natural processes formed early organic compounds Disproven by Redi and Pasteur Miller-Urey experiment Biogenesis = living organisms only come from other living organisms REDI & PASTEUR THE ORIGIN OF CELLS Prokaryotes – Archaebacteria (1st cells) Eukaryotes – endosymbiont hypothesis Separate DNA in chloroplasts and mitochondria Both organelles the same size and shape of bacteria