Earth Science 13.4 Cenozoic Era : Age of Mammals

1. Earth Science 13.4 Cenozoic Era : Age of Mammals Cenozoic Era : The Age of Mammals

2. The Age of Mammals The Age of Mammals: (65 m – present) • If the Mesozoic was the “Age of reptiles” the Cenozoic can be called the “Age of Mammals”. • During the Mesozoic, mammals were mainly small scavengers and plant eaters. • After the Cretaceous extinction, mammals began to adapt to environments and expand in their diversity. Mammals of the Cenozoic

3. The Age of Mammals The Age of Mammals: • Mammals succeeded during the Cenozoic because of adaptations that enabled them to out compete the surviving reptiles. • For example, because mammals are warm-blooded, they can live in cold environments and search for food any time of day or time of year. • Other adaptations include more efficient hearts and lungs than reptiles, and the development of insulating body hair or fur. • These adaptations allowed mammals to lead more active lives than reptiles. Mammals of the Cenozoic

4. The Age of Mammals The Tertiary Period: • During the Tertiary period (65 – 1.5 million), mountain building and climate changes accompanied the breakup of Pangaea. Mammals became widespread and diverse worldwide. • Major fragments of Pangaea became separate continents during the Tertiary. • Seas separated North America from South America and Europe from Africa. • Plate movements led to major mountain building activity in western North America (the Rockies), Europe (the Alps) and India (the Himalayas).

5. The Age of Mammals The Tertiary Period: • Generally, climates during the Tertiary period were cooler than those of the Cretaceous. • The mid-Tertiary had temperate dry climates. • Later in the period, Earth’s climates cooled leading to the development of large continental glaciers in Antarctica about 10 million years ago.

6. The Age of Mammals Tertiary Life: • The Tertiary saw the development of many new species, from songbirds to snakes. • The major development of the Tertiary was the evolution of many new types of mammals. • Mammals evolved specialized limbs and teeth for particular environments. • For example, meat-eaters evolved sharp teeth for cutting and tearing. Rodents developed self-sharpening teeth for gnawing. Plant eaters developed flat molars for chewing.

7. The Age of Mammals Tertiary Life: • Some animals evolved to take advantage of a rich new food source; grass. • As the climate became cooler and drier, vast grasslands developed. • Many types of grazing animals, including the ancestors of cattle and horses, evolved during the Tertiary.

8. The Age of Mammals Quaternary Period: (5.3 – 0) • Two factors have greatly affected life on Earth during the Quaternary period : • The advance and retreat of continental glaciers (which have formed and melted about 30 times in the last 3 million years) • And the migration of homo sapiens (humans) to every corner of the Earth

9. The Age of Mammals Quaternary Period: (5.3 – 0) • A map showing the physical features of Earth 2 million years ago would look much the same today. • But beginning in the late tertiary, a series of ice ages covered large parts of the northeast hemisphere with continental glaciers.

10. The Age of Mammals Quaternary Period: (5.3 – 0) • Because Earth is a complex system, many factors determine whether Earth’s climate becomes cold enough for an ice age. • These factors include ocean currents, the size of the ice covered areas, and the affects of living things on the atmosphere.

11. The Age of Mammals Quaternary Period: (5.3 – 0) • In the 1940’s, astronomer MilutinMilankovitch proposed that three different cycles, related to Earth’s movements, were the main cause of ice ages. • These cycles are called the Milankovitch cycles.

12. The Age of Mammals Quaternary Period: (5.3 – 0) • For example, there is a 100,000 year cycle related to changes in the shape of the Earth’s orbit. • Earth receives more or less energy from the sun depending on it’s position within each of these cycles.

13. The Age of Mammals Quaternary Period: (5.3 – 0) • Milankovitch thought that ice ages occur when solar energy reaching Earth is at a minimum. • Scientists today think that Milankovitch cycles provide a “partial” explanation for recent ice ages.

14. The Age of Mammals Quaternary Life: (5.3 – 0) • One trend in evolution during both the Tertiary and Quaternary periods was that some mammals became very large. • During the ice ages, many large mammals lived in the cold grasslands, or steppe, that bordered the ice covered regions of North America.

15. The Age of Mammals Quaternary Life: (5.3 – 0) • These animals included mastodons and mammoths, which were both huge ancestors of the elephant. • In North America, there were also giant beavers, ground sloths, wolves. bears, sabre-tooth cats and bison. • All these animals became extinct about 10,000 years ago, at the end of the last ice age.

16. The Age of Mammals Quaternary Life: (5.3 – 0) • How can the extinction at the end of this last ice age have occurred? • Scientists have multiple theories. No single explanation provides a complete answer.

17. The Age of Mammals Quaternary Life: (5.3 – 0) • Some scientists suggest disease or climate change played an important role in their demise. • Still other scientists suggest that humans hunted large animals down to the point of extinction. • Other skeptics question whether small groups of humans could have caused so many different species to all go extinct all at once.

18. The Age of Mammals Quaternary Life: (5.3 – 0) • Modern Homo sapiens evolved from ancestors in Africa more than 100,000 years ago. • The fossil record shows that about 50,000 years ago early humans began to migrate out of Africa. • Soon, the range of early humans extended from Europe, Africa, and Asia to Australia.

19. The Age of Mammals Quaternary Life: (5.3 – 0) • Than, as sea level fell during the last ice age, a land bridge formed that connected Asia with North America. • Scientists think this land bridge enabled humans to migrate to the Americas about 14,000 years ago.

20. The Age of Mammals Quaternary Life: (5.3 – 0) • Today, Homo sapiens - humans inhabit every continent. Our species has become the most powerful factor in changing Earth’s environment; for the better or worse. • This in turn affects the other species with whom we share the planet.