History of Life on Earth How Did Life Begin? The Age of the Earth: The Earth formed about 4.5 billion years ago according to evidence obtained by radiometric dating.
History of Life on Earth Measuring Earth’s Age: Radiometric Dating is the estimation of the age of an object by measuring its content of certain radioactive isotopes.
History of Life on Earth Measuring Earth’s Age: • An isotope is a form of an element whose atomic mass (the mass of each individual atom) differs from that of other atoms of the same element. • Isotopes Commonly used for Radiometric Dating • IsotopesHalf-life(years)Effective Dating Range(years)Dating SampleKey Fission Product Lutetium-176 Hafnium-176 37.8 billion early Earth Uranium-238 Lead-206 4.468 billion 10 million to origin of Earth Uranium-235 Lead-207 704 million 10 million to origin of Earth Rubidium-87 Strontium-87 48.8 billion 10 million to origin of Earth Potassium-40 Argon-40 1.277 billion 100,000 to origin of Earth Carbon-14 Nitrogen-14 5730 ± 40 0-100,000 • Note: the half-life durations listed in the text sections of this tutorial are rounded off foruranium-238 and potassium-40.
History of Life on Earth Measuring Earth’s Age: Radioactive isotopes , or radioisotopes, are unstable isotopes that breakdown and give off energy in the form of charged particles (radiation). The breakdown, called radioactive decay, results in other isotopes that are smaller and more stable. The time it takes for one-half of a given amount of radioisotope to decay is called a radioisotope’s half life.
History of Life on Earth The Evolution of Cellular Life: The Evolution of Prokaryotes: When did the first organisms form? To find out, scientist study the best evidence of early life that we have, fossils. A fossil is the preserved or mineralized remains (bone, tooth, or shell) or imprint of an organism that lived long ago.
History of Life on Earth The Evolution of Prokaryotes: Two Groups of Prokaryotes: Eubacteria are prokaryotes that contain a chemical called peptidoglycan in their cell walls. They include many bacteria that causes disease and decay.
History of Life on Earth Two Groups of Prokaryotes: Archaebacteria are prokaryotes that lack peptidoglycan in their cell walls and have unique lipids in their cell membranes. Chemical evidence indicates that the first eukaryotic cells were more likely to have evolved from archabacteria.
History of Life on Earth The Evolution of Eukaryotes: About 1.5 billion years ago, the first eukaryote appeared. • Are much larger than a prokaryote. • Have complex system of internal membranes. • DNA is enclosed in nucleus. • Almost all have mitochondria. • Chloroplast, which carry out photosynthesis, are found in protists and plants. • Mitochondria and chloroplasts are size of pro • karyotes, and they contain their own DNA.
History of Life on Earth Animal and Bacterial Cells:
History of Life on Earth Mass Extinctions: Extinctions is the death of all members of a species. Mass extinction is an episode during which large numbers of species become extinct. The 3rd and most devastating of all mass extinctions occurred at the end of the Permian period, about 245 mya. About 96% of all species of animals living at the time became extinct. The fifth mass extinction which occurred 65 mya, brought about the extinction of about 2/3 of all land species, including the dinosaur.