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Geologic Time Scale the division of the Earth's history into time units based on the life-forms that lived only during certain periods eons the longest subdivisions of geologic time is based upon the abundance of certain fossils eras after eons, it is the longest subdivision of time and is marked by major, striking, and worldwide changes in types of fossils; these units of time are divided into periods periods are units of geologic time characterized by the types of life existing worldwide at that time; two of these units of time are divided into epochs epoch this is the shortest unit of geologic time; they are characterized by differences in life-forms, but some of the differences can vary from continent to continent. organic evolution fossil record shows that species have changed over geologic time species a group of organisms that normally reproduces only with other members of their group natural selection a process by which organisms with characteristics that are suited to a certain environment have a better chance of surviving and reproducing than organisms that do not have these characteristics artificial selection breeding of animals to obtain specific characteristics; Example: breeding domestic animals trilobites exoskeleton consists of three lobes that run thelength of the body; it has a heaad, a segmented middle section and a tail index fossils fossils of creatures that indicates that they lived everywhere on the Earth for a short period of time: trilobites Pangea a giant landmass or supercontinent Precambrian Time the longest part of Earth's history and includes the Hadean, Archean and Proterozoic Eons; lated about 4.5 billion to 544 million years ago; rocks from this time have been so deeply buried that they have been changed by heat or pressure Cyanobacteria blue-green algae thought to be one of the earliest forms of life on Earth; first appeared about 3.5 billion yers ago; contained chlorophyll and used photosynthesis; then oxygen became a major atmospheric gas during Pre-Cambrian Time unusual life-forms during Pre-Cambrian Times similar to modern jellyfish, worms, and soft corals; many were bottom dwellers Paleozoic Era era of ancient life; 544 million -248 million years ago; traces of life easier to find in this era; warm shallow seas covered land and most life forms were marine; invertebrates and first vertebrates with backbones evolved during this era; many ancient fish had lungs and gills Appalachian Mountains formed during the Paleozoic era; it occurred as the ocean separating North America from Europe and Africa closed End of Paleozoic Era more than 90% of all marine species and 70 % of all land species died off; continental plates came together and formed the supercontinent Pangaea; glaciers formed over most of its southern part; mountain building processes caused seas to close and deserts to spread over North America and Europe possible cause of extinction of the dinosaurs a large asteroid or comet collided with Earth around 248 million years ago causing wide-spread smoke blocking the sun and killing plant life; OR extreme volcanic activity great enough to block the sun and affect the entire globe Mesozoic era 248-65 million years ago; marked by rapid movement of Earth's plates; Era of middle life; at the beginning of this era, all continents were a single landmass or Pangaea; Panagea separated into Laurasis (north mas) and Gondwanaland (south mass) then broke up into present-day continents; reptiles adapted readily to drier climates & became the most conspicuous animal during the Triassic Period Dinosaurs during the Mesozoic Era of the Triassic Period the first small dinosaurs appeared; large dinosaurs appeared during hte Jurassic and Cretaceous Periods; new species of dinosaurs evolved and othe species became extinct; they may have been warm or cold blooded What is know about the dinosaurs? Many nests have been found together and it is believed that the mothers nurtured their dinosaurs babies or young. Birds in the Mesozoic Era they appeared during the Jurassic Period; believed to have evolved from small, meat-eating dinosaurs; not believed to be direct ancestors of today's birds Mammals of the Mesozoic Era first appeared in the Triassic Period; they were small, mouse-like creatures; they were warm-blooded vertebrates that have hair covering their bodies & females produced milk to feed their young Gymnosperms in the Mesozoic Era first appeared in the Paleozoic Era & dominated the land; they are platns that produce seeds but not flowers; pines and ginkgo trees angiosperms during the Meszoic Era flowering plants first evolved during the Cretaceous Period; these plants produce seeds with hard out;er covering; they are the most diverse and abundant land plants today; magnolia and oak trees End of the Mesozoic Era ended around 65 million years ago; major extinction of land and marine species; dinosaurs disappeared; maybe an asteroid collided with Earth; great extinction Cenozoic Era era of recent life; began about 65 million years ago and continues today; it is divided into 2 periods: Tertiary and Quaternary and the 2 periods are divided into 7 epochs (PEOMPPH) What is the Cenozoic Era known for? mountain building period with cooler climates Cenozoic mammals they became dominant with many new life-forms appearing after the dinosaurs disappeared; expanding grasslands favors grass eaters like horses, cattle, camels, deer, elephants, etc. Cenozoic Marsupials mammals like kangaroos, loalas and wombats that carry their young in a pouch When did Homo Sapiens probably appear on Earth? around 140,000 years ago; fossils suggest that humans were hunters Palezoic = Early Life = ______ & ______ Trilobites in oceans & first land plants Mesozoic = Middle Life = _____ & ______ dinosaurs roam Earth & abundant gymnosperms Cenozoic = recent life = ______ & ______ mammals common & abundant angiosperms A change in the hereditary feature of a species over a long period is _________. organic evolution A record of events in Earth history is the ____________. geologic time scale The largest subdivision of geologic time is the ___________. eon The process by which the best-suited individuals survive in their environment is ___________________. natural selection A group of individuals that normally breed only among themselves is a _______. species How many millions of years ago did the era in which you live begin? 65 million years What is the process by which better suited organisms survive and reproduce? natural selection During what period did the most recent ice age occur? Quaternary what is the next smaller division of geologic time after the era? period What was one of the earliest forms of life? cyanobacterium During which era did the dinosaurs live? Mesozoic Which type of plant has seeds without protective coverings? gymnosperms Which group of plants evolved during hte Mesozoic Era and is dominant today? angiosperms In which era did the Ediacaran fauna live? Precambrian A student thought she found a dinosaur bone in Pleistocene sediment. Is this possible? It is not likely because dinosaurs became extinct long before the Pleistocene Epoch.