Chapter 36

1. Chapter 36 A Brief History of the Earth Presented by April Senger

2. Geologic Time • If the 4.5 by the Earth is estimated to be were compacted into one year… • The Earth would start forming from matter on January 1 • The oldest known rocks would appear at the end of February • Simple bacterial life would appear in the sea at the end of March • Complex plants & animals would appear in late October and early November • Dinosaurs would rule in mid-December & die out by December 26 • Humans would appear at 11:50 p.m. on the evening of December 31 • All human history would occur in the last minute of New Year’s Eave Presented by April Senger

3. Uniformitarianism • The Earth’s history is recorded in the rocks • The present is the key to the past • Our class will cover the highlights of the history of the Earth • There are entire classes dedicated to studying the Geologic Clock and events • The Earth itself is thought to contain 4.5 by of history Presented by April Senger

4. Relative Age of Rocks 5 Principles help us compare layers and geologic events to determine which came first, second and so on • 1. Original horizontality – layers are laid horizontally. If layers are at an angle, it indicates they were moved into that position by a crustal disturbance after deposition • 2. Superposition – The oldest layers are on the bottom and youngest are on top Presented by April Senger

5. Principles Continued • 3. Cross-cutting – An igneous intrusion or fault that cuts through pre-existing rock is younger than the rock through which it cuts • 4. Inclusion – Inclusions are pieces of rock contained within another. An inclusion is older than the rock containing it • 5. Faunal succession – Fossils follow a set pattern in their history & development. Studying the fossils in layers tells us the sequence the rocks were formed based on the time of the fossil Presented by April Senger

6. Unconformities • Weathering, erosion, crustal uplifts, etc interrupt the normal sequence of deposition • There are breaks and gaps in the rock record • We find the gaps or unconformities by observing the relationships of layers and fossils Presented by April Senger

7. Angular Unconformity & Nonconformities • Angular unconformities is we see tilted or folded sedimentary rocks that are overlain by horizontal younger rock layers • Erosion can occur between layers erasing part of the rock record • Nonconformity is when overlying sedimentary rock are found on eroded metamorphic or intrusive igneous • This indicates large amounts of uplift & erosion before sedimentary layers were deposited Presented by April Senger

8. Concept Check • If a granitic intrusion, a dike for example, cuts into or across sedimentary layers, which is older: the granite or the sedimentary layers? • The intrusion is new • If a layer is cut, it was there first Presented by April Senger

9. Radiometric Dating • Relative dating can tell us younger and older but not an absolute age • To get a span of time, we use radiometric dating • More simply we use radioactive isotopes and the ratios they exist in to estimate an age • Common isotopes are U-238, U-235, K-40 & C-14 (fossils) • The oldest material found is 4.4 bya and the oldest rock is 3.8 bya Presented by April Senger

10. Concept Check • Could carbon-14 be used for dating rocks in the Precambrian time (see page 644 for Geologic Time Scale) • Note: the Precambrian is estimated to occurred 3956 mya • Carbon dating is only good for the last 50,000 years due to its short half life Presented by April Senger

11. Precambrian • The Precambrian stretches from 4.5 bya to 544 mya when abundant macroscopic life appeared • This is 85% of the Earth’s history • It is difficult to study because most of the rocks have been recycles and the life didn’t have hard parts to leave a good fossil record • The Earth was oceanless, extremely volcanic, riddled with meteorites until 4 bya when is slowed Presented by April Senger

12. Moving Forward • The volcanic gases produced a primitive atm and the ocean • The atm was rich in water vapor but void of O • The first simple fossils were found 3.4 bya • Stromatolites were the remains of wavy layers of algae that lived in shallow seas (photosynethic) • The oxygen produced led to an ozone layer Presented by April Senger

13. A Very Slow Process • The first cells reproduced asexually and had no nucleus. 1. 5 bya the first nucleated cells formed • The first multicellular plants/animals appeared 700 mya • Australian fossil records show soft bodied jelly fish to worms • The evidence showed us the first animal communities in marine waters Presented by April Senger

14. Continental Precambrian Changes • The first evidence of plates moving was 2.5 bya • About 1.5 bya Siberia merged into the western edge of North America • Europe was converging with the eastern region of North America • Others converged from the south to form the first super continent long before Pangaea Presented by April Senger

15. The Break Down • We break the remaining time into Eras (Paleozoic, Mesozoic & Cenozoic), then Periods & finally Epochs • There are more subdivisions that can be studied in detail in a more advanced class • See page 644 for quick reference Presented by April Senger

16. The Paleozoic Era • It spanned from 544 mya to 300 mya • Sea levels rose and fell several times • Marine life flourished • Life forms changed from marine invertebrates to fishes, amphibians & reptiles • Fossils containing shells helped preserve organisms • There are 6 periods in the Paleozoic Presented by April Senger

17. Cambrian Period • The Cambrian is marked by an explosion of life forms • All most all forms of marine life developed during this period • Organisms secreted calcium carbonate and calcium phosphate exoskeletons leaving excellent fossil records • Organisms could withstand more UV rays, moved into shallower habitats & the skeletal support allowed them to grow bigger • Example: Trilobite or cockroach of the Cambrian Sea Presented by April Senger

18. Ordovician Period • Life continued to explode • Earliest appearance fo vertebrates with the jawless fishes (agnatha) • The end of the period brought many extinctions thought to be a result of widespread cooling and glaciation • Tropical shallow-water marine groups were the most affected • High-latitude and deep-water organisms were relatively unaffected Presented by April Senger

19. Silurian Period • Life begins to emerge on land • Most of North American was at or above sea level • Shallow seas were vanishing as thick gypsum and evaporite minerals accumulated • Terrestrial plants appeared including vascular plants • Terrestrial plants were tied to the wet lands • Land animals included scorpions and millipedes Presented by April Senger

20. Devonian Period • Known as the “Age of the Fishes” • Plants become wide spread –seed ferns, scale trees and true ferns • Boney fish and lobed fish flourished • The lobed fish developed internal nostril so they could breath air • The lungfishes and coelacanth (means living fossil) are similar to these first fish Presented by April Senger

21. More Fish • Lobed fish also had the ability to use their fins to walk due to jointed appendages, lobed fins and defined muscles • Evolutionists propose that these animals gave rise to the land animals • Amphibians (relative to the lobed fish) appeared at the end of the period • They were significant because they lived on land but had to return to water to lay their eggs Presented by April Senger

22. The Carboniferous Period • Time of the Great Swampy Forests • It includes the Mississipian and Pennsylvanian periods • Warm and moist climate to lush vegetation and swampy forests which are now the source of coal beds in North America, Europe, and northern China Presented by April Senger

23. Ewe…Giant Bugs • Insects underwent rapid changes and became giants • Examples: cockroaches and dragonflies (wingspan of 80 cm) • Evolution of the first reptiles appeared with the amniote egg (self contained and porous shell) • Amniotic eggs allowed animals to cut the dependence on water and fully transition to land Presented by April Senger

24. The Permian Period • The beginning of the Age of Reptiles • They ruled for 200 my (humans have only been here for 100,000 years) • Two land reptiles groups emerged: diapsids & synapsids • The diapsids were less dominant and are the predecessors to the dinosaurs • The synapsids are like the fin-backed pelycosaur (fin used in temperature regulation) Presented by April Senger

25. What A Finale • The end of this period ended in one of the largest extinctions in fossil records • 95% of marine species and 70% of land species died out • The cause is still debated and might be linked to worldwide cooling, glaciations & a drop in sea level for about 20-25 million years • Terrestrial animals took a less drastic impact that others feel were a direct result of plate tectonic activity as the continents formed Pangaea Presented by April Senger

26. Pangaea • During the Devonian and Permian Periods, all major land masses collided once more to form Pangaea • They hadn’t been joined since 600 my before during the Precambrian • The Appalachians in NA, the Hercynian and Caledonian Mountains in Europe, and the Ural Mountain in Russia formed • The drastic collision was powerful enough to form the Rocky Mountains so far inland • The southern climate was mainly dominated by glaciers because it was very close to the South Pole Presented by April Senger

27. Mesozoic Era • When dinosaurs rule the Earth • “The Age of Reptiles” • Made up of the Triassic, Jurassic & Cretaceous periods • Mammals were small and insignificant compared to the dinosaurs • Land plants greatly diversified and true pines and redwoods spread Presented by April Senger

28. More of the Mesozoic • Flowering plants arose in the Cretaceous and become the dominant plant by the end of the period • The insects benefited greatly by flowering plants • The Cretaceous ended 65 mya in another mass extinction where the dinosaurs, flying reptiles, marine reptiles & many nonreptiles both on land and sea were wiped out Presented by April Senger

29. The End To An Era • The extinction was thought to have resulted from the impact of a large meteorite • Large layers of iridium have been found worldwide in this period • The meteorite is thought to have sent up a dust cloud creating a nuclear winter knocking out the food supplies and chilling the Earth • A meteorite of this size would have caused acid rain, tsunamis, wildfires, and delayed greenhouse effect • Some feel the iridium came for massive volcanic eruptions • Last, others propose that the impact came from an extraterrestrial object • The Cretaceous marked the end of the Mesozoic Era Presented by April Senger

30. Mesozoic Tectonics • Pangaea started its initial break up • The breakup ended at the end of the Triassic period with the eruption of a basalt flow with into two major rift zones • One of these rifts separated NA formng the Atlantic Ocean • During the Jurassic, India stared N, SA/Africa separated from Aurstralia/Antartica • The plates are still moving today • During the Triassic period, the Farallon Plate and related accretions to the NA continent started creating volcanism, grantitic batholiths, and mountain belts sill rimming te Eastern Pacific Basin Presented by April Senger

31. The Cenozoic Era • Time or Age of the Mammal • It is made of the Tertiary and Quaternary periods • These periods are broken into the Paleocene, Eocene, Oligocene, Miocene & Pliocene Epochs for the Tertiary and Pleistocene and Holocene Epochs for the Quaternary • We are currently in the Quaternary Presented by April Senger

32. Empty Niches • After the mass extinctions, many niches were vacant and the mammals quickly took over the habitat left by their predecessors • Flying bats, large land mammals, & marine animals such as whales and dolphins were some successful organisms • Climates cooled as characterized by the widespread glaciations of the Pleistocene • The ice age is considered be continuing today with alternations between glacial and interglacial conditions Presented by April Senger

33. Glacier Impacts • Glaciers can cover as much as 1/3 of the land • The glaciers left their mark on the continents…literally • Humans were thought to have evolved • The continents were in similar locations to that of today but lower water levels created land bridges (Bering Strait) • This bridge allowed migration from Asia to North America • There were extinctions in large land mammals that might be explained by the arrival of man in NA, stone hunters in Africa & varying temperatures Presented by April Senger

34. Cenozoic Tectonics • The Tertiary period had a spreading center off the western margin of NA, with the Pacific plate on the west and Farallon plate on the east • This occurred 30 mya and gave birth to the San Andreas Fault • Baja California was torn away from the Mexican mainland and the Gulf of California was created • The plates are still moving today and eventually California and Baja CA will completely detach or find themselves joined to western Canida Presented by April Senger

35. Hot Topic…Rather Hot Spot • The Hawaiian Island or Emperor Seamount Chain orginaly was a northbound plate • When the collision of the NA plate and Pacific ridge system occurred at the same time the island change started to travel NW • The bend in the chain occurred between 30-40 mya Presented by April Senger