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  1. EARTH AND SPACE SCIENCE Chapter 9 A View of Earth’s Past 9.3 The Mesozoic and Cenozoic Eras

  2. 9.3 The Mesozoic and Cenozoic Eras Objectives • List the periods of the Mesozoic and Cenozoic Eras. • Identify two major geologic and biological developments during the Mesozoic Era. • Identify two major geologic and biological developments during the Cenozoic Era.

  3. Introduction • The greatest extinction event known to have occurred marks the boundary between the Paleozoic and Mesozoic Eras. • The Permian-Triassic mass extinction claimed 90% of marine species and 70% of terrestrial species. • The surviving life forms had a number of niches available to exploit as a result of the loss of so many species. • Adaptive radiation of surviving species into newly vacated niches resulted in an abundance of new life forms appearing on Earth at this time. • Some of these life forms flourished while others went extinct.

  4. The Mesozoic Era • The Mesozoic Era of time spans from about 251 million years ago to 65 million years ago. • As Pangaea broke into smaller continents, plates drifted and collided. • The Sierra Nevada (California) and Andes (South America) began to form. • In general, the climate for much of the Mesozoic was warm and humid with many shallow seas and marshes. • The Mesozoic is known as the Age of the Reptiles due to the diversification and abundance of many forms of reptiles – including the dinosaurs!

  5. The Mesozoic Era • The Triassic was the first period of the Mesozoic. • Dinosaurs first appear in the fossil record in Triassic rocks. • Dinosaurs ranged in size from smaller than a chicken to 30 m long weighing over 15 tons, though most Triassic dinosaurs were 4 m to 5 m long and moved quickly. • Lush forests with cone bearing trees and cycads dominated much of the landscape, though there were arid regions more like today’s deserts.

  6. The Mesozoic Era • The Triassic oceans contained ichthyosaurs (marine reptiles that had adapted a fish-like shape) and invertebrate cephalopods called ammonites. • Ammonites diversified so rapidly, were widespread, and readily identified so they are often used as Mesozoic index fossils. • Small, rodent-like forest dwellers also appeared during the Triassic.

  7. The Mesozoic Era • Two major groups of dinosaurs had evolved to become the dominant form of life by the Jurassic Period. • The hip-bone structure is used to distinguish the two major groups of dinosaurs. • The saurischians (lizard-hipped dinosaurs) include herbivores, and carnivores. • The sauropods, like Apatosaurus – 50 tons and 25 m long, were among the largest of the dinosaurs.

  8. The Mesozoic Era • The ornithischians (bird-hipped dinosaurs) included only herbivores. • Stegosaurus (9 m long, 3 m tall) was one of the better known ornithischians. • Pterosaurus, a flying reptile, was common in the Jurassic skies. • Archaeopterix, one of the earliest undisputed birds, dates back to the Jurassic Period.

  9. The Mesozoic Era • The most popular of all dinosaur species, Tyranosaurus rex, lived during the late Cretaceous Period. • T. rex stood up to 6 m tall and was about 15 m long. • Ankylosaurs, ceratopsians, and hadrosaurs were also common during this final period of the dinosaurs’ reign. • The earliest angiosperms (flowing plants) appeared during the Cretaceous. • Magnolias and willows were among the most common of these early flowering plants.

  10. The Mesozoic Era • The Cretaceous Period (last of the Mesozoic Era) ended with a mass extinction that brought about the end of the dinosaurs and many large marine reptiles. • Some scientists have credited the movement of continents (plate tectonics) and volcanic activity for this mass extinction. • A more popular explanation among many scientists is the impact hypothesis which credits the mass extinction to a meteorite impact. • The impact raised dust which blocked much of the sun’s light for months or even years.

  11. The Mesozoic Era • The lack of sunlight reaching the Earth caused obvious problems for most plant life and cooled the Earth’s climate considerably. • The rapid climate change and destruction of much vegetation precipitated a domino effect among the animals on Earth. • An iridium layer is found in the very last layer of Cretaceous rocks to be deposited at may sites globally. • Iridium is a common element in meteorites, but very rare on Earth.

  12. The Cenozoic Era • The Cenozoic Era is the unit of geologic time that began about 65 million years ago and continues through modern day. • The continents have migrated to their current position and mountain chains such as the Alps in Europe and the Himalayas have been uplifted. • Major climate changes have occurred throughout the Cenozoic. • At times, continental ice sheets have covered nearly 33% of the Earth’s land mass. • Mammals have reached an amazing degree of diversity during this time, also known as the Age of Mammals.

  13. The Cenozoic Era • The Tertiary Period of the Cenozoic Era spans time from 65 million years ago up to the time before the last series of ice ages (about 2.6 million years ago). • The Quaternary Period includes the last 2.6 million years of Earth’s history – ice ages and the modern Holocene Epoch.

  14. The Cenozoic Era • During the Paleocene, the earliest epoch of the Cenozoic, many new mammals evolved such as small rodents and early primates. • These Paleocene primates were much like today’s prosimian primates. Purgatorius

  15. The Cenozoic Era • Many mammal forms diversified in the Eocene epoch including whales, bats, and the earliest known horses. • Alabama’s state fossil is the Eocene whale Basilosaurus cetoides (left).

  16. The Cenozoic Era • Worldwide, the climate became significantly cooler and dryer in the Oligocene Epoch. • In this cooler climate (average temperature had already dropped an average of 4°C by the end of the preceding Eocene Epoch), grasses, hardwoods, and conifers flourished. • Many early species of mammals became extinct as larger mammals became more predominant such as deer, horses, pigs, camels, cats, and dogs. • Marine invertebrates continued to diversify.

  17. The Cenozoic Era • During the Miocene Epoch, the Antarctic icecap began to form as circumpolar currents began to form around the continent. • Tectonic forces and falling sea levels caused the Mediterranean Sea to dry up and fill several times. • The largest of land mammals, the Paraceratherium transouralicum (4.5 m tall, 15 tons), lived during this time. • The earliest of the saber-toothed cats date back to the Miocene Epoch.

  18. Paraceratherium transouralicum

  19. The Cenozoic Era • Predators such as bear, dog, and cat families evolved into modern form. • Large herbivores, such as the giant ground sloth flourished during this time. • Giant ice sheets began to spread near the end of the Pliocene Epoch – a drop in sea level occurred as a consequence of water being trapped in ice. • The Bering land bridge was exposed between Eurasia and North America and the isthmus of Panama formed between Central America and South America. • The presence of the bridges allowed for migration of species to previously inaccessible land.

  20. The Cenozoic Era • The Pleistocene Epoch began about 1.8 million years ago and lasted until about 11,500 years ago. • Many ice ages occurred during the Pleistocene Epoch. • Some animals adapted to cooler weather with thick fur coats while others migrated. • Fossils of the earliest modern humans are found in Pleistocene deposits. • Some early humans in the late Pleistocene left cave paintings.

  21. The Cenozoic Era • The Holocene Epoch (a.k.a. Recent Epoch) began about 11,500 years ago around the end of the last glacial episode. • During that time, ice sheets have melted and sea level has risen about 140 m. • Homo sapiens developed agricultural methods and metal tools. • Compared to the history of life on Earth, human history is rather brief.

  22. References • Triassic Scene (Coelophysis) - • Thrinaxodon - • Ichthyosaurs - • Dinosaur Pelvis Comparison -

  23. References • Stegosaurus - • Pterosaur - • Archaeopteryx - • Tyrannosaurus rex (both images) -

  24. References • Triceratops - • Cladogram of Land Plants - • Cretaceous Impact Site - • Impact Illustration -

  25. References • Ice Age Move Image - • Purgatorius - • Basilosaurus cetoides - • Horse Evolution -

  26. References • Eocene Bat - • Indricothere - • Wooly Rhino - • Mammoth -

  27. References • Cave Painting - • Egyptian Wheat Farmer - • Grinnell Glacier Photos - • Sea Level Rise -