Geologic Time

1. Geologic Time

2. Methods of Dating Rocks • Relative dating - Using fundamental principles of geology (Steno's Laws, Fossil Succession, etc.) to determine the relative ages of rocks (which rocks are older and which are younger). • Absolute dating - Quantifying the date of the rock in years. This is done primarily by radiometric dating (or analysis of the breakdown of radioactive elements in the rocks over time).

3. Geologic Time Scale • The geologic time scale has been determined bit-by-bit over the years through relative dating, correlation, examination of fossils, and radiometric dating. • Boundaries on the time scale are drawn where important changes occur in the fossil record, such as extinction events.

4. Geochronologic Units The geologic time scale is divided into a number of types of units of differing size. From the largest units to the smaller units, they are: • Eons • Eras • Periods • Epochs These units are geochronologic units. Geochronologic units are time units.

7. Eons Eons are the largest division of geologic time. • Precambrian - oldest rocks on Earth • (2.5 billion to 542 million years ago) Beginning of life. • Phanerozoic Eon - "visible life" (542 million years ago to present)

8. The Precambrian The Hadean, Archean and Proterozoic eons are together referred to as the Precambrian, meaning “before the Cambrian Period”. The Precambrian covers 87% of geologic history.

9. Precambriandivisions Hadean Eon, informal division of Precambrian time occurring between about 4600 million (4.6 billion) and about 3800 million years ago. The Hadean Eon is characterized by Earth’s initial formation—from the accretion of dust and gases and the frequent collisions of larger planetesimals. Throughout part of the eon, impacts from extraterrestrial bodies released enormous amounts of heat that likely prevented much of the rock from solidifying at the surface. As such, the name of the interval is a reference to Hades, a Greek translation of the Hebrew word for hell. During this time the moon was formed by a collision between Earth and a planetoid. The first atmosphere escapes, and the second atmosphere is formed. www.brittanica.com Written by John P. Rafferty Last Updated 4-12-2012

10. Precambriandivisions The Archean Eon began about 3800 million years ago with the formation of the Earth’s crust and extended to about 2500 million years ago. Surface of the Earth cools from molten to solid rock. Water starts to condense and atmosphere consists of nitrogen and carbon dioxide. First evidence of the earliest primitive life-forms—bacteria and blue-green algae—appears in rocks about 3.5 billion (3500 million) years old. Archean greenstone-granite belts contain many economic mineral deposits, including gold and silver. Oldest record of Earth’s magnetic field. www.Britannica.com Written by Brian Frederick Windley

11. Precambriandivisions Proterozoic Eon - starting about 2500 million years ago to about 544 million years ago. First stable continents appear, first free oxygen in atmosphere. Creation of banded iron formations. As anaerobic organisms are poisoned by oxygen, single celled photosynthetic organisms proliferate. Formation of the ozone layer blocks radiation from the sun. First Eukaryotic cells appear. Supercontinents form and break up. Soft bodied organisms and shelled invertebrates appear. 650 million years ago, mass extinction of 70% of dominant sea plants is caused by global glaciation.

12. Eras There are three eras in the Phanerozoic Eon. Eras are divided into geologic periods. In order from oldest to youngest, the three eras are: • Paleozoic Era - "ancient life" (such as trilobites) • Mesozoic Era - "middle life" (such as dinosaurs) • Cenozoic Era - "recent life" (such as mammals)

13. Periods Eras are divided into periods.

14. Paleozoic Era • Permian Period • Pennsylvanian Period • Mississippian Period • Devonian Period • Silurian Period • Ordovician Period • Cambrian Period (oldest)

15. Cambrian Period (542 to 488.3 mya) - Abundance of multicellular life. - Most of the major groups of animals first appear    - 510 mya: Vertebrates appeared in the ocean.   - first trilobites The Ordovician Period (490 to 443 mya. - Best known for diverse marine invertebrates, including trilobites, brachiopods, primitive fish, cephalopods, corals, criniods, gastropods.

16. gastropod crinoid brachiopod cephalopod

18. Silurian Period • Melting of large glacial formations contributed to a rise in sea levels • Coral reefs appear • First freshwater fish • First fish with jaws • First evidence of life on land • Proliferation of Ordovician species

19. Devonian Period • First vascular plants • First seed plants • First tetrapods (reptile) • First terrestrial arthropods • Sea life abundant • Soils before this time were predominantly red, after soils were dark due to organic accumulation. • Glaciation and lowering of the sea level triggered a mass extinction at the • end of the Devonian.

20. Devonian Period Life

21. The Mississippian and Pennsylvanian Periods are known as the Carboniferous Periods • Rich deposits of coal found in beds from this time due to vast amounts of tropical plant material • First amniotic eggs allow tetrapods to lay eggs without fear of desiccation • Trilobites become scarce, heavily armored Devonian fish become extinct, more modern looking fish appear. Mississippian Period – environment was heavily marine, with seas covering part of the continent. Pennsylvanian Period – environment is alternating marine and terrestrial, with transgression and progression of seas caused by glaciation.

22. Mississippian/Pennsylvanian Period

23. Permian Period (the Great Dying) • Biggest mass extinction recorded in the history of life on Earth (loss of most of the marine invertebrates of the time) • Great forests of ferns died off leaving room for plants with enclosed seeds • Loss of earlier species makes way for the age of dinosaurs

24. Late Permian land masses

25. Mesozoic Era • Cretaceous Period • Jurassic Period • Triassic Period (oldest)

26. Mesozoic Era Meso (middle) zoic ( life or animals) is the time between the Paleozoic (ancient life) and the Cenozoic (New life) Began with the Permian extinction, the largest extinction event in the history of the Earth. Ends with the Cretaceous-Paleogene extinction event, which killed off non-avian dinosaurs.

27. Triassic Period (248 to 213 mya) Named for three distinct rock layers from this time period found throughout Germany and NW Europe. These are red beds, capped by chalk, followed by black shale.

28. Triassic Period The supercontinent Pangea existed at the beginning of the Triassic, but began to split apart in two separate landmasses, Laurasia and Gondwana. • Environment was hot, vast deserts and warm seas. Even the polar regions had forests. • First mammals and dinosaurs appear • After the continent breakup – more extinctions. http://stevengoddard.files.wordpress.com/2011/07/g-44.gif%3Fw%3D640

29. Herrerasaurus – one of the first true dinosaurs, 10 ft long and 100 to 400 lbs. Eoraptor – only about 20 lbs. Also one of the first known dinosaurs http://faculty.etsu.edu/gardnerr/planetarium/dino/triassic.htm http://www.walkingwithdinosaurs.com/dinosaurs/detail/herrerasauru paleontologist

30. Jurassic Period(213 to 145 mya) Primitive mammals are still around, the descendants of which are with us today: duck bill platypus, marsupials like kangaroos and opossum. Birds make an appearance. But dinosaurs ruled the Jurassic. The tallest and largest creatures that ever existed on Earth came into being, while some reptiles moved back into the sea. (dinosaur = thunder lizard) http://www.hudsonfla.com/1hst.htm

31. Jurassic Period(213 to 145 mya) Archaeopteryx, known as the first bird Megazostrodon – first mammal during the Jurassic period. Mammals could not dominate during the reign of the dinosaurs, as the dinosaurs were huge. http://dinosaurs.about.com/od/dinosaurbasics/tp/12bestdinos.htm Stegosaurus – known for its tiny brain

32. Jurassic Period(213 to 145 mya) Allosaurus was smaller, faster and more vicious than the better known (and later) T-Rex, and may have hunted in packs Giant sauropods were very successful during the Jurassic http://dinosaurs.about.com/od/dinosaurbasics/tp/12bestdinos.htm jurassic dinosaurs

33. Cretaceous Period (145 to 65 mya) • Named for the Latin word for chalk. However in many parts of the world formations from this period are limestone from the shallow seas. • Longest period of the Phanerozoic. • Warm climate, lots of inland seas • Lots of marine animals and birds, but dinosaurs dominate on land • First flowering plants appear

34. Cretaceous Period • The end of the Cretaceous is marked by an iridium rich layer found worldwide thought to be associated with the impact crater that created the Gulf of Mexico. • There is also evidence of a series of huge volcanic eruptions along the tectonic border between India and Africa that began just before the impact. It is likely that these regional catastrophes combined to precipitate climatic change. • These climate changes are most likely what brought about the demise of all dinosaurs with the exception of birds • http://www.livescience.com/29231-cretaceous-period.html#sthash.3pzQoyXQ.dpuf

35. The diversity of life in the Cretaceous was unparalleled, including a large number of large marine animals, as well as flying dinosaurs

36. Tyrannosaurus rex is part of the carnivorous groups of dinosaurs that, according to new research, maintained a stable level of biodiversity leading up to the mass extinction at the end of the Cretaceous. http://www.livescience.com/29231-cretaceous-period.html#sthash.3pzQoyXQ.dpuf Titanosaurs, such as this Alamosaurus were herbivores that thrived during the late Cretaceous.

37. Cenozoic Era Eras are divided up into Periods • Quaternary Period (youngest – today) • Tertiary Period (oldest)

38. Epochs Periods can be subdivided into epochs

39. Epochs of the Cenozoic Era • Holocene Epoch (youngest - today) • Pleistocene Epoch • Pliocene Epoch • Miocene Epoch • Oligocene Epoch • Eocene Epoch • Paleocene Epoch (oldest)

40. Paleocene (65 – 55.5 mya) • Paleocene means “old recent” • Starts with mass extinction event - the remaining dinosaurs die out • Early Paleocene Earth was dark and cold due to clouds of dust • Late Paleocene was almost as warm and humid as the Cretaceous.

41. Mammals were still small • Birds were plentiful, some were huge predatory meat eaters • Example: Gastornis – stands 6.5 ft, eats meat, does not fly. Crocodiles survived, also snakes. Example: Titanoboa – 50 ft long and weighing more than one ton.

43. Eocene Epoch (55.5 – 33.7 mya) • Similarities in plants and animals in North America and Europe indicate these regions were still in contact or very close

44. Eocene • First appearance of perissodactyls – odd toed herbivores that would become horses, zebras, donkeys, tapirs, rhinos First appearance of artiodactyls – even toed herbivore/omnivore that would become pigs, cows, sheep, goats, giraffes, hippos and camels and Whales!

45. Oligocene (33.7 – 23.8 mya) • Spread of newly evolved grasses opened a new niche for grazing animals. Early horses and proto-camels abound in North America Continents are near their present day locations. Decrease in average global temperatures

46. In South America, several very large animals evolve Pyrotherium – elephant like hooved animal about 10 ft long and 5 ft tall Indricotherium,, a close rhinoceros relative, was the largest land mammal to ever live, at about 5.5 meters (18 feet) tall at the shoulder, 9 meters (30 feet) long, weighing around 20 tons. http://prehistoric.ucoz.ru/img/tm/Pyrotherium.jpg

47. Miocene (23.8 – 5.3 mya) 20 million years ago, Antarctica was covered by ice and the northern continents were cooling rapidly.  The world has taken on a "modern" look, but notice that Florida and parts of Asia were flooded by the sea. http://www.scotese.com/miocene.htm

48. Dense forests give way to open deserts, tundra and grasslands. • Herbivores become faster, large predatory animals and birds dominate. • Increased seasonality. Chalicothere, a Miocene mammal from Kazakhstan. Chalicothere was an odd-toed hoofed mammal, or Perissodactyl Desmostylus hesperus, an amphibious mammal from the Miocene that lived in North America and Eastern Asia. (Source: Wikimedia Commons, artist Nobu Tamura.

49. Pliocene (5.3 – 1.8 mya) • During large chunks of the Pliocene epoch, Eurasia, North America and South America were all connected by narrow land bridges--and it wasn't all that difficult for animals to migrate between Africa and Eurasia, either. This resulted in increased competition, displacement and even outright extinction. For example, camels (like the huge Titanotylopus) migrated from North America to Asia. Apes and hominids were mostly restricted to Africa, though there were scattered communities in Eurasia and North America as well. The first land bridge connecting North and South America led to the demise of many South American species of animals. • dinosaurs.about.com/od/CenozoicEra/a/Pliocene-Epoch.htm‎

50. Some familiar mammals appeared, such as the Woolly Mammoth, Saber Toothed Tigers, and the Giant Sloth (7 meters tall) and Giant Armadillo (weighed 1 ton)