Unit 1B Lesson 4 History of Life on Earth How do we learn about ancient life? Paleontologists scientists that studies fossils Fossil- a trace or imprint of a living thing that is preserved by geological processes. What can we learn from fossils? Fossil record- all of the fossils discovered worldwide. By examining fossils we can identify all species that have lived and died Two ways to describe the age of fossils 1. Relative dating determines whether a fossil formed before or after another fossil o Newer fossil are above and older fossils are below 2. Absolute dating- estimates the age of a fossil in years o Estimations are based on radioactive elements in certain rocks near the fossil The fossil record gives us an overall understanding of patterns of change. Over generation populations change Fossils preserve these changes Some species are present for long periods of times, others for shorter Extinctions When every individual of a species dies. Mass extinction occur when large numbers of species go extinct Reasons- gradual environmental change, asteroids, etc. These are documented in the fossil record Geologic Time scale The standard method used to divide Earth s long 4.6 Billion year history Eon: Largest division of the time scale Era: Characterized by the largest group of organisms alive at that time Periods: subdivision of Eras Epochs: subdivision of Periods 1. Precambrian time Started 4.6 Billion years ago (BYA) Ended 542 Million years ago (MYA) Broken up into three eons: Hadean, Archean, Proterozoic
A. First organisms Prokaryotes, found in oceans, no oxygen o Around 3 Billion years ago Cyanobacteria used sunlight to produce energy and oxygen o Oxygen filled the atmosphere and the ozone layer formed o Ozone blocks harmful radiation from the sun. o Before the ozone layer life could only survive in oceans and underground. B. Multicellular organisms evolved o Increased oxygen allowed new organisms to evolve around 1 BYA o Single celled eukaryotes formed o Then multicellular eukaryotes formed C. Mass Extinction occurred o Increased oxygen killed some organisms o Microscopic organisms do not preserve well (little known about them) 2. Phanerozoic Eon Started - 542 MYA Ended Today (still going) A. Paleozoic era Started 542 MYA Ended 251 MYA Periods Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian o Fossils rich in animals and plants o Include sponges, corals, snails, trilobites, fish (earliest backbone), sharks o Life moved to land o Plants, fungi, air breathing animals o All major plant groups except flowering plants appeared o Crawling insect among first on land then large salamanders o Giant fern forests, reptiles, flying insect by the end of the era o Permian mass extinction (largest) 96% of marine species became extinct B. Mesozoic Started 251 MYA Ended 65.5 MYA o Age of the Reptiles (Dinosaurs) o First birds and mammals appeared o Most important plants were the conifers (cone bearing) o Flowering plants arrived in the late Mesozoic o Mass Extinction (asteroid hit Yucatan Peninsula) o 2/3 all land species went extinct
C. Cenozoic Era Started 65 MYA Ended Still going today Periods tertiary, quaternary Epochs Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene o Mammals dominated this Era o Humans appeared o Climate has changed many times during this era o During ice ages many creatures moved to the equator, adapted to cold or died o Primates include humans, apes, monkeys o Eyes are located in front of skull, five digits (opposable thumb)
Possible Essay Questions: A. Explain the difference between relative and absolute dating? B. Explain how a scientist might use fossils to explain how a mass extinction occurred? C. Put the following time periods in order and explain what it was like in each: Mesozoic, Precambrian, Cenozoic, and Paleozoic. D. What are two reasons that mass extinctions occur? E. Put the following events in order (1-7) Humans appear Cyanobacteria produce oxygen Age of Reptiles Ozone layer forms First Plants Permian mass extinction Earth is created F. What could we predict would happen to organisms if the global temperatures increased by ten degrees?