Chapter 15 – Geologic History

l Much of what we know about the history of life on earth is from _________________

• Radiometric dating of fossils has allowed scientists to follow the evolution of many life forms, from bacteria to plants and animals

• The changes noted by following the fossil record are generally _______________ changes

• Major changes in the organization of organisms

• These changes have been used to assemble the geologic record

l Geologic Record

• The history of Earth has been divided into three eons:

• ____________

§ From the origin of Earth until the appearance of Eukaryotes

• ___________

§ Dominated by simple eukaryotic organisms

• Phanerozoic

§ Explosion of multicellular life forms to modern times

l Phanerozoic is further divided into three Eras:

• ___________

• Ancient animal

• ___________

• Middle portion of “modern” life – middle animal

• ___________

• Time during which modern lineages of life emerged – recent animal

§ Each of these Eras is further divided into Periods and Epochs

l Important Events

• Paleozoic Era

• ~550 – 250 mya

• Cambrian explosion

§ Sudden appearance of many animal phyla

• Colonization of land

§ _______ first

§ Then _________

§ Followed by ___________

§ And finally ____________

• Mass extinction occurred at the end of the Paleozoic

• Mesozoic Era

• ~250 – 65 mya

• Time of the “ruling reptiles”

§ Dinosaurs ruled land, air, and sea

• Origin of both __________ and ____________

• Cone bearing plants dominate early, replaced later by flowering plants

• During the Mesozoic, continents begin to move

• Another mass extinction marks the end of the Mesozoic

• Cenozoic Era

• ~65 mya to present

• Mammals and birds take over as the dominant life forms – often referred to as the “age of mammals”

• Mammals and birds both undergo an explosion of diversity

• Much of the Cenozoic has been marked by dramatic climate changes as well as by continued continental drift

l Mechanisms of Macroevolution

• Continental Drift

• Based on available evidence, all of the land masses on earth have come together to form a supercontinent at least 3 times

• The most recent was ~250 mya

• ___________ is the name given to this single continent

• Plate tectonics (movement) have slowly been moving land masses to their present positions

• The formation of Pangea – and it’s breakup – led to many important changes in animals and plants

• Continental Drift

• Pangea split ~180 mya into Laurasia and Gondwana

§ This split resulted in massive allopatric speciation

• India collided with Asia ~55 mya forming the Himalyayan mountains

• Isolated areas such as Australia developed vastly different life forms than other areas that were still connected

• Mass Extinctions

• At least ____ major mass extinctions are recorded in the fossil record

• The most recent resulted in the extinction of the dinosaurs

• Evidence suggests that a massive climate change resulted from a large asteroid impact near the Yucatan peninsula of Mexico

§ Resulting dust in the atmosphere blocked sunlight, causing global cooling, decreased photosynthesis, and ultimately mass extinctions

• While these results seem catastrophic, large scale extinctions leave large “holes” in the environment

• Following each mass extinction, adaptive radiations occur

• Adaptive Radiation

• Single types of organisms “radiating” into many kinds

• Usually associated with some type of “release”

§ Competitive pressures removed

§ New resources become available

§ New adaptations allow organisms to take advantage of previously unavailable resources