Chapter 22 The Precambrian Earth

Precambrian Time: -includes everything before the ________ period of the Paleozoic era -length of about ___ billion years -88 % of earth’s history -much historical evidence destroyed Cambrian 4

Barringer Crater How did this feature form? Do you think events like this were more or less common? Impact from meteor more

Crust Formation Differentiation: -_______ materials sink toward center and _______ materials accumulate near surface heavier lighter

Precambrian _______ – core of Archean and Proterozoic rocks; ________ rocks in North America; make up craton Shield oldest

_________ – ancient continent _____ billion years ago Laurentia 1.8

_________ – first _______________; ______million years ago Rodinia supercontinent 750

Precambrian Atmosphere Volcanic Outgassing: -produced atmosphere of _____________, carbon dioxide, nitrogen, and carbon monoxide, but not __________ water vapor oxygen

Oxygen Producers Stromatolites: -large mats of ________________ -dominated shallow __________ of Proterozoic -nearly identical to those found in ___________ today cynobacteria oceans Australia

Oxygen Evidence Banded Iron Formations: -alternating layers of _________ and _______________ -result of locally high __________ levels in early Proterozoic chert iron oxides oxygen

Early Life _____________ – single cell organism; no nucleus;only life before Proterozoic; includes cynobacteria __________ – contains nucleus; larger Prokaryote Eucaryote

__________ – shallow marine organisms of 670 to 570 million years ago; extinct before_________ era begins Edicara Fauna Paleozoic

Chapter 22 Review What is the commonly accepted age of the Earth? What is the process by which a planet becomes internally zoned? What is the name of the first supercontinent that formed near the end of the Proterozoic? 4.6 billion years differentiation Rodinia

Chapter 22 Review (continued) 4. Describe the major difference between Earth’s early atmosphere and explain how this occurred. 5. Describe the difference between prokaryotes and eukaryotes and tell which is older. Prokaryotes are smaller, have no nucleus, are less complex, and came first. Today’s atmosphere contains oxygen given off by photosynthetic plants.