Chapter 9: HISTORY OF EARTH The Essential Earth, 2 nd Edition Thomas H. Jordan & John Grotzinger History of Earth Earth is 4.56 Billion Years Old Earth has experienced a rich and diverse history that we will explore in this chapter 2012 by W. H. Freeman and Company Formation of the Solar System The Solar System Nebular Hypothesis Matter within a given orbit accretes together to eventually form planets Leads to formation of planets that rotate within orbits around the sun Inner rocky planets formed from the accretion of dense materials Outer gaseous planets formed from the accretion of less dense materials Note: Pluto is no longer a planet as of 2006 Early Earth Earth was very hot at its origin Violent impacts from planetesimals and other bodies were common Elements within Earth differentiated to form layered internal structure Early Earth: A Giant Impact!
Early Earth: Differentiation Early Earth: Atmosphere & Oceans Light elements that make up our atmosphere and oceans were aggregated to Earth from planetesimals Volcanic degassing fed the molecules to early atmosphere and oceans Early History of Inner Planets Earth had largely differentiated by 4.4 Billion years ago Other inner planets experienced similar differentiation during this time Significant differences are evident in the relative sizes of these planets cores Earth s moon preserves a history of early solar system events since its crust has not been constantly recycled through plate tectonic processes Early History of Inner Planets Moon s surface provides a record of impact bombardment history Earth: Evolution of the Continents Continental crust contains the oldest crustal material on Earth Continents are divided into tectonic provinces, which are large scale regions formed by a particular set of tectonic processes. North America provides a well known example of tectonic provinces North American Provinces
Canadian Shield Interior Platform Precambrian basal rocks (same as on Shield) are overlain by Paleozoic sedimentary rocks Basin and dome structures Basins accumulate relatively thick sedimentary packages Oldest part of the North American crust Precambrian granitic and metamorphic rocks Appalachian Fold Belt N. American Cordillera Deformation from multiple Paleozoic orogenies Records the history of the assembly of Pangaea Global Tectonic Provinces Other continents have similar tectonic provinces Continents are built by orogenic activity around stable continental nuclei called cratons Cratons consist of Precambrian shield and platform rocks Deformation from Mesozoic and Cenozoic tectonic activity Records the history of the Farallon Plate beneath North American continent Continental Growth Magmatic addition: In subduction zones, differentiation of silica rich rock produces new continental crustal material Vertical Process Accretion: Fragment of buoyant, continental crust becomes attached to the edge of a craton through tectonic processes Horizontal Process Accreted terrains can be identified along continental margins
Continental Modification Orogenies modify continents through Metamorphism Thickening of continental crust Uplift Production of structural features such as thrust faults and fold India Eurasia collision provides a modern example of orogenic activity Melting of lower crust Continental Modification Example: Assembly of Pangaea Multiple orogenies associated with the assembly of Pangaea modified the North American continent The Wilson Cycle: Evolution of Continents Geologic Record of Wilson Cycle & Supercontinents Biological Events in Earth History Biological Events in Earth History The evolution of life is recorded in the rock record by fossils Life in all three domains has originated from a common, universal ancestor Early evidence of life comes from microfossils and chemical traces of life
Microbes Dominated in the Precambrian Stromatolites are sedimentary features that provide evidence of abundant microbial communities for much of Earth s history Oxygenation of Precambrian Atmosphere Banded Iron Formations Grypania fossils Red Beds Geologic features provide evidence of the build up of free oxygen in the Precambrian oceans and atmosphere as a result of photosynthetic activity A second step in oxygenation is observed at the end of the Precambrian (600 Million years ago) Cambrian Explosion In the Cambrian period, a major radiation of life occurred All major groups of animals alive today originated during this radiation Cambrian Explosion Examples of fossils from before (Namacalathus) and after (Hallucigenia and Trilobites) the Cambrian Explosion History of Animal Diversity Marked by Radiations & Extinctions