Geologic Time Test • I can/can do/will know….(see the pink writing on the slides) – List how old the Earth is slide 2 – Explain how the start and endings of the divisions on the Geologic Timeline are determined. slide 2 – Explain how scientists know all about Earth’s past slide 5 – Define what an index fossil is and how it is a slam dunk in determining the age of a rock layer. slide 5 – Place in order, by length, the time spans: Epoch, Era, Eon, and Period. (longest to shortest) slide 6 – Explain how an organism's size/complexity tells us about its position on the Geologic Timeline. slides 7-12 – List what eon and era we live in slides 8 &12 – When the dinosaurs disappeared and why slide 10 – Given fossil evidence, make conclusions about what events have taken place in history. slide 11 Geologic Time Scale • Helps us study Earth’s pastwhich is really old (estimated 4.6 billion years old) • Divides Earth’s history into intervals of time determined by --major events/changes in the rock layers, and --the appearance/disappearance of fossils/life Slow Changes on our Earth •Mountain forming •Climate •Erosion •Weathering Fast Changes on our Earth • Volcanic Eruptions • Earthquake • Flood How do we know what has happened all this time? • Fossil information – Tells us what life existed when • Rock layers/sequencing – Tells the relative age & what the environment was like • Index fossils have a wide distribution world-wide, live for a short period of time in one particular time span, and help date the layer(s) they are found in. • Fossilized seashells found in the mountains tells us that there was no mountains there long ago, just seafloor. • Fossilized corals on land indicates that a previous ocean environment existed there. Divisions & sizes of Geologic Time spans • Eon-largest unit of time (Earth’s history has four eons) • Era- A division of an Eon. The most recent eon is divided into three eras: Paleozoic, Mesozoic, and Cenozoic. • Periods-Each era is subdivided into a number of periods. • Epoch- The periods of the Cenozoic, the most recent era, are further divided into epochs “Pre-Cambrian Time” • Makes up 90% of Earth’s History • Hadean, Archean, and Proterozoic eons make up the Pre-Cambrian Time • Fossil record dominated by tiny, single celled organisms that can only be seen with a microscope (bacteria) and soft bodied animals that didn’t fossilize (like jellyfish) • Earth cooled, continents formed Phaneorozoic Eon (our current eon) •Divided into 3 Eras: •Paleozoic- “ancient life” •Mesozoic- “middle life” •Cenozoic- “recent life” Paleozoic Era • 542 mya to 251 mya • All life lived in the ocean at the start. Multi-celled life • Early Paleozoic =Age of the Invertebrates • Middle Paleozoic =Age of the Fishes Vertebrates & insects evolve and first plants • Late Paleozoic =Age of the Amphibians Life started to move on land. Reptiles evolve. Pangaea and mountain ranges form • Mass extinction happened at the end (248 mya)90% of all species perished. • • • • • Mesozoic Era 250 mya to 65 mya Bigger and more complex life Age of the Reptiles (dinosaurs dominate) Pangaea breaks up Sm. mammals, birds, and flowering plants first appeared & evolve. • N. America covered by a sea • A mass extinction event (asteroid?) 65mya killed off 50% of all species (& the dinosaurs) – from the heat at the impact site, – lack of sunlight and thus photosynthesis world-wide, & – other catastrophic impact effects (tsunamis, earthquakes, etc) KT Asteroid • Is thought to have caused the mass extinction of the dinosaurs as evidenced by the lack of fossil size & diversity afterwards • Happened 65 million years ago Cenozoic Era • • • • 65 mya to present day (our current era) Age of Mammals –biggest and most complex life Ice Age happened during this time Mammoth, saber-toothed cats and other large mammals common during the first part of this time are now extinct • End of era natural land bridges allowed first humans and animals to spread around the planet.