Transcript File
Earth and Radioactive Dating History of Life - Part 1 Before Life Existed on Earth: • • • • 1st, Formation of the Universe, (then) Formation of the Solar System (then)Formation of the Earth (then)Environment able to support life had to come about on Earth Universe • • • • What is the universe? What is matter? What is the opposite of everything? Is the Universe static? Unchanging? Finite or infinite? Olbers' Paradox (1823*) • The argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe. The BIG BANG Theory • This is the event in which the universe was formed. • All matter and radiation in the universe came into being during the Big Bang. • Happened 13.7 (or 15) billion years ago. Our Solar System • Formed out of a solar nebula about 5 billion years ago • Earth formed at same time as other planets (4.6 billion years ago) A Time Line (sort of) Earth • Formed by accretion • Started out as rocky ball of uniform composition and density • Then began to melt from the inside • May have collided with another protoplanet and remelted • 4.6 -4.1 billion years ago I Don’t Believe This • Or is it that I don’t understand? Formation of Earth • The next layer was formed by the gases escaping from the interior of the earth as it cooled. 4.1 -3.8 billion years ago (no oxygen) ATMOSPHERE • Photosynthetic organisms added oxygen to the atmosphere.(2.8 billion years ago) 78% Nitrogen & 21% Oxygen Formation of Earth • Water from Earth, clouds, rain from atmosphere • Earth was bombarded by water-rich (ice)asteroids/comets. This created our next layer(starting about 4 billion years ago HYDROSPHERE • All the water in, on and around the earth. Formation of Earth • The narrow layer around the earth’s surface in which life can exist is called the BIOSPHERE • Can be related to the skin on an apple. What is a million? • How long would it take to count to a million? Well, counting once per second (easy at the start, but tough when you reach the hundred thousand mark), eight hours per day, seven days per week (no weekends off), it would take you a little over a month to count to one million! Big Numbers • http://wimp.com/budgetcuts/ Now 2 “oldies” • Remember these slides from last semester?????? ISOTOPE • An atom with a different than usual number of neutrons in the nucleus. • Usual Carbon has 6P +6N = 12 C12 • Some Carbon may be 6P +8N = C14 RADIOACTIVITY • Some isotopes are radioactive. • That means their nuclei are unstable and break down over time. • As they break down, energy is released from the nucleus. • Radioactivity can be good or bad. Radioactivity • Some atoms are unstable • Radioactivity is the process whereby unstable atomic nuclei release energetic subatomic particles. The word radioactivity is also used to refer to the subatomic particles themselves. This phenomenon is observed in the heavy elements, like uranium, and unstable isotopes, like carbon-14. Measuring Absolute Time • Original radioactive isotopes, called parent isotopes, decay into stable isotopes (daughter isotopes) by the process of fission. • During fission, an atom splits into 2 atoms. Half-Life • The isotope decays at a constant rate that is measured by the isotope’s half-life. • Half-life is the time it takes for half of the parent isotopes to decay into daughter isotopes. Half – Life of some elements Carbon14 • Radioactive isotope of Carbon • Living organisms are constantly adding carbon to their bodies, some of which is C14 • When an organism dies, no new carbon is entering the body, and radioactive decay takes place, C14 decays to N14 • Using ratio of C14 to N14 allows you to calculate number of half-lives, and then the age of the sample of once living material See other powerpoint • On radioactive decay Radioactive Isotope Dating • Process of measuring ratios of parent to daughter isotopes in a sample to determine absolute age of the sample Use of radioactive/radiometric dating • By using various radioactive isotopes found in rocks, minerals, and organic materials (bone fragments, wood, ashes), scientists can date when rocks were formed, or when something died or was burned. • This is a basic tool used to determine the geologic time scale – organization of how old different rocks and fossils are Geologic Time • Starts with the formation of the earth approximately 4.6 BILLION years ago. • Still developing into current time. • How do we know? – Layers of the crust – Fossils (most form in sedimentary rock) – Radioactive dating Fossils • Preserved remains or evidence of an ancient organism • Organic material has usually been replaced by inorganic rock/minerals • Dinosaur track – Clayton Lake State Park • Ammonite fossil, Cabezon, NM • 17” across • Coelophysis fossil uncovered at Ghost Ranch, New Mexico, in 1947. • http://www.blm.gov/n m/st/en/prog/more/pal eontology.html Geologic Time Charts • Visual representation of Earth’s geologic history • Shows names for the different time intervals • Note the heirarchy of names – Eon, Era, Period, Epoch • **** Note that the chart is organized with youngest, most recent events on top, oldest on bottom Precambrian • 90% of earth’s history (longest time) • First life forms 1. Single- celled, prokaryotic type (bacteria) • Anaerobic organisms 2. Photosynthetic organisms (added oxygen) 3. Eukaryotes Paleozoic • • • • • • Cambrian Ordovician Silurian Devonian Carboniferous Permian – Mass Extinction • Diversity of marine life • 95% of the life in the oceans disappeared at the end of Era. Mesozoic • Age of reptiles • Earth warmer than it is today • Break up of Pangaea • Cretaceous • Jurassic • Triassic Cenozoic • Tertiary • Quaternary • Age of the mammals • Lived on land, in water and in the air. Geologic Time • • • • 99% of all living organisms have gone extinct Fossils occur in a specific order Early life was single cellular Liquid water was needed for life to start Fossil rock • http://www.youtube.com/watch?v=ClJ5lwl_ wM0&list=PLvgILFwoRX2luskEUC5XKfzC jmaLnGUse&index=1 Fossil Record • Millions of fossils have been discovered. • Fossils occur in sequences – observations dating from the 1700’s • Fossils prove that humans did not exist alongside dinosaurs. • Scientists can check accuracy of radioactive dating by using different isotopes Important dates/ages (in years ago/years before present) • • • • • • Earth formation – 4.6 billion Oldest rocks – 3.8 billion Oldest life – 3.5 billion– anaerobic bacteria Oldest eukaryotic – 1.5 billion Oldest multicellular – 1billion “Explosion” of life – 544 million (shells)