Views of Earth’s Past

 Geologists divide Earth’s past into different time periods based on specific traits  For the Time Scale, scientists  Used clues preserved in the rock record  Fossils are important evidence

 Eons –  Longest periods of time  There are 3 Archean Oldest Rocks– begins with formation of Earth’s Crust Almost 4 Billion years ago Proterozoic Began 2.5 Billion Years Ago Contains earliest fossils, none of which are land based Phanerozoic Characterized by visible signs of life

 Eons are divided into Eras  Phanerozoic Eon has 3 Eras Paleozoic 543 million years ago Fossils of both land and plant organisms Mesozoic DINOSAURS! RAWR! Cenozoic 65 million years ago Continues today Ice ages, human fossils

 The Earth has changed a lot  Some dramatic, some not  Ex. Over time, earth’s movement has changed so that our year is a few days shorter than an early paleozoic year  Landmasses appeared, then vanished  Global climate has warmed, then cooled, then warmed, then cooled…  Early atmosphere was mostly carbon dioxide, sulfur dioxide, water vapor and nitrogen

 Showed up when photosynthetic organisms developed (like algae)  Level of Oxygen in atmosphere increased gradually

 Fossil evidence indicates early organisms were very simple  Ex. Grand Canyon  Top layers – land reptiles, ferns, insects  Middle layers – marine fossils  Lower layers – few shells, traces of worms  Bottom layers- no fossils at all

 Fossil records show disappearance of species and emergence of others  Indicates a changing pattern of life forms

 States that organisms that have favorable traits survive to pass them on to new offspring  Many organisms’ fossil records show long periods of being unchanged  Then, there appears to sometimes be a quick change (in a million years or less)  Still a debate over gradual vs. abrupt evolution

 Common way of referring to everything before the Cambrian period of the Paleozoic era

 Precambrian makes up the majority of earth’s past  Approx. 4 billion years  Rocks are hard to date  Timeframe is HUGE  Rocks are severely bent and folded  Often lack fossils  Craton is the oldest rock. An exposed area of this is called a shield.

 Found in rock 3.5 billion years old  Early organisms resemble bacteria (cyanobacteria)  Stacked mats of bacteria and sediment form stromatolites  Make up the greatest amount of precambrian fossils

1. Cambrian Period a. Evidence for first vertebrate life b. Only marine fossils are found c. Trilobites- most common

2. Ordovician Period a. Fossils similar to Cambrian b. Also all ocean animals c. Graptolite used as index fossil for this period

3. Silurian Period a. Appearance of land animals/plants b. Ocean fossils similar to previous time c. Seas over North America dry up d. Eurypterids were common

4. Devonian Period a. Age of fishes I. Giant, jawless and jawed fish b. First forests c. North America collides with a continental fragment, building parts of Appalachian Mountain Chain

5. Carboniferous Period a. Appearance of reptiles b. Insect numbers increased c. Major swamps in Northeast us I. These later became the coal deposits in Pennsylvania, West Virginia etc.

6. Permian Period a. Dry Climate b. A great ice age covered parts of South America, Australia, South Africa and India c. Lots of mountain ranges were built because of plate movement d. First mass extinction near end of period

 Began 248 million years ago  Divided into Triassic, Jurassic, Cretaceous  Mild Climate  No Glacial Ice at Poles

 MYA  First Dinosaurs  Many were small  Some adapted to the sea

 Ammonites  Important Index Fossils  Worldwide at the time  Almost extinct at end of period

 Triassic Plants  Tree Ferns  Spore-bearing ferns  Conifers Conifers at Arizona’s Petrified Forest National Park

 Land formations  At this time, most land was connected in Pangaea  At end of triassic, land began to split apart Laurasia –North America and Europe Gondwanaland – The remaining continents

 mya  Dinosaur types increased  Larger dinosaurs were more common  First true mammals (rodent-like)  First metamorphic animals appear (butterflies etc.)  Bird-like fossils

 Jurassic Plants  Ferns Declined  Mosses, conifers abundant

 Ocean formation  South Atlantic Ocean began to open  Indian and North Atlantic Oceans had formed by end of period  Huge sea covered most of central and western North America

 MYA  Largest Dinosaurs  T-Rex  Brontosaurus

 Cretaceous Plants  Conifers  Appearance of flowering plants  Deciduous trees  Sequoia

 Cretaceous Geology  South Atlantic becomes major Ocean  Australia and Antarctica still joined, as were North America and Eurasia

 50% of species perished  Climate Change?  Rise of Mammals?  Drop in Sea level?  Volcanic Eruptions?  Asteroid Impact? Dinosaur Extinction

 Cenozoic Era began 65 MYA  Divided into 3 periods  Paleogene – 41 million yrs.  Neogene – 22 million yrs.  Quaternary – 2 MYA to NOW!

 Cenozoic Climate  Early- warm and humid  Later – ice ages  Life  Rise of mammals  Rise of modern plants  Geology  Continents move to current locations

 Almost all major mountain ranges today developed during these periods  Himalayas, Appalachians, Rockies, Sierra Nevadas, Andes, Alps

 Eastern and western coastal plains of U.S. – underwater  Western U.S. Volcanically Active  Yellowstone area covered in lava and ash several times

 Mostly mild  Favored Tropical Plant Growth  Many trees grew in Greenland and Northern Canada

 Temperatures dropped  Tropical plants were driven further south  Hardy Grasses Survived

 Increased in number and frequency  Many smaller versions of what exist today lived  Small horses  Camel  Elephant

 2 MYA until now  Many periods of glacial advance and thawing  First epoch, Pleistocene, Called ‘great ice age’

 Temps warmed up  Tropical plants died off everywhere but around equator

 Hominid – general term for modern human or ancestor  Oldest remains, 4.5 million years old  Most recent  400,000 – 300,000 yrs old called Homo sapiens  Neanderthals, Cro- Magnon  Fossil record is difficult to trace because we’ve only been here 2-4 million years.