Chapter 9 HISTORY OF EARTH

Transcription

1 Chapter 9 HISTORY OF EARTH FIGURE 9.2 The solar system. This diagram shows the relative sizes of the planets as well as the asteroid belt separating the inner and outer planets. Though considered one of the nine planets since its discovery in 1930, Pluto was demoted from that status by the International Astronomical Union in With this revision, there are only eight true planets, not nine. Jack Schmitt, the only geologist to have done field work on the moon. The study of lunar geology, including the dating and analysis of rocks, has helped us to understand even more about the geologic history of Earth! Jack was trained by geologists from the US Geological Survey. FIGURE 9.3 Computer simulation of the impact of a Mars-sized body on Earth. [Solid-Earth Sciences and Society. Washington, D.C.: National Research Council, 1993.] FIGURE 9.1 The nebular hypothesis explains the formation of the solar system. FIGURE 9.4 The differentiation of early Earth resulted in a zoned planet with three main layers.

2 FIGURE 9.5 Early volcanic activity contributed enormous amounts of water vapor, carbon dioxide, and other gases to the atmosphere and oceans. Later, photosynthetic microbes removed carbon dioxide and added oxygen to the primitive atmosphere. Hydrogen, because it is lighter, escaped into space. FIGURE 9.8 Astrogeologist Eugene Shoemaker (at left, pointing with hammer) leads an astronaut training trip on the rim of Meteor Crater, Arizona, in May (An aerial view of Meteor Crater is shown in Figure 2.7.) [U.S. Geological Survey.] FIGURE 9.6 The Moon has two types of terrain: the lunar highlands, with many craters, and lunar lowlands, or maria, with few craters. Maria look darker due to presence of widespread basalts that flowed across their surface over 3 billion years ago. The highlands are lighter because abundant craters reflect sunlight better. Jordan, The [NASA.] Essential Earth 1e 2008 by W. H. Freeman and Company FIGURE 9.9 By calibrating the relative time intervals from crater counting with the Jordan, absolute The Essential ages Earth 1e of 2008 lunar by W. H. rocks, Freeman and geologists Company have constructed a geologic time scale for the terrestrial planets. (Ma, million years ago.) FIGURE 9.10 Mercury has an ancient, geologically dormant surface similar to that of Earth s Moon. [NASA/JPL/Northwestern University.] FIGURE 9.7 The number of impacts varies over time. The planets were formed by a chain of collisions that tapered off over the first 500 million years of their evolution. Jordan, The Essential However, Earth 1e 2008 there by W. was H. Freeman a and later Company phase, known as the Late Heavy Bombardment, that peaked around 3.9 billion years ago. (Ga, billion years ago.)

3 FIGURE 9.11 The prominent scarp that snakes across this image is thought to have formed as Mercury was compressed, possibly as the planet cooled following its formation. Note that the scarp must be younger than the craters it offsets. [NASA/JPL/Northwestern University.] NASA s 2010 Messenger mission to Mercury! FIGURE 9.13 Many surface features on Venus were formed by ongoing geologic activity. (b) Volcanic features called coronae are not observed on any other planet except Venus. The visible lines that define the coronae are fractures, faults, and folds produced when a large Jordan, blob The of Essential hot Earth lava 1e collapsed 2008 by W. H. Freeman like a and fallen Companysoufflé. Each corona is a few hundred kilometers across. [Images from NASA/USGS.] FIGURE 9.12 A comparison of the solid surfaces of Venus, Earth, and Mars, all at the same scale. The topography of Mars, which shows the greatest range, was measured in 1998 and 1999 by a laser altimeter aboard the orbiting Mars Global Surveyor spacecraft. That of Venus, which shows the smallest range, was measured from 1990 to 1993 by a radar altimeter aboard the orbiting Magellan spacecraft. Earth s topography, which is intermediate in range and dominated by continents and oceans, has been synthesized from altimeter measurements of the land surface, ship-based measurements of ocean depth, and gravity field measurements of the seafloor surface from Earth-orbiting spacecraft. [Greg Neumann/MIT/GSFC/NASA.] FIGURE 9.14 (a) Olympus Mons on Mars is the tallest volcano in the solar system, with a summit almost 25 km above the surrounding plains. Encircling the volcano is an outward-facing scarp 550 km in diameter and several kilometers high. Beyond the scarp is a moat filled with lava, most likely derived from Olympus Mons. [NASA/USGS.] FIGURE 9.13 Many surface features on Venus were formed by ongoing geologic activity. (a) Maat Mons, a volcanic mountain that may be up to 3 km high and 500 km across. [Images from NASA/USGS.] FIGURE 9.14 (b) Valles Marineris is the longest (4000 km) and deepest (up to 10 km) canyon in the solar system. It is five times deeper than the Grand Canyon. In this image, the canyon is exposed as series of fault basins whose sides have partially collapsed (such as at upper left), leaving piles of rock debris. The walls of the canyon are 6 km high here! The layering of the canyon walls suggests deposition of sedimentary or volcanic

4 FIGURE 9.18 An aerial view of ancient, eroded metamorphic rocks in Nunavut, Canada, exposed on the surface of the Canadian Shield. [Roy Tanami/Ursus Photography.] FIGURE 9.15 Spirit (right ), one of the Mars Exploration Rovers, is about the size of a golf cart. Spirit is standing next to a twin of Sojourner, a rover that was sent to Mars in [NASA/JPL.] Hematite concretions were found on Mars, hinting the presence of water; see FIGURE 9.16 A sedimentary sequence exposed along the flank of Endurance crater, photographed by the rover Opportunity. (a) An interpretive drawing showing each stage in the history of the outcrop. (b) The vertical succession of layers in the outcrop preserves an excellent record of early Martian environments. [NASA/JPL/Cornell.] FIGURE 9.19 A map of the interior platform of North America, showing its basin and dome structure. The basins are nearly circular regions of thick sediments, whereas the domes are regions where the sediments are anomalously thin. Basement rocks Jordan, The are Essential exposed Earth 1e 2008 by on W. H. the Freeman tops and Company of some domes, such as the Black Hills and the Ozark Dome. FIGURE 9.17 The major tectonic provinces of North America reflect the processes that formed the continent. FIGURE 9.20 The Appalachian Mountain region of the south and central eastern United States, with an aerial view to the northeast and an idealized cross Jordan, section. The Essential The Earth 1e major 2008 by W. physiologic H. Freeman and Company subregions extend from west to east in order of increasing intensity of deformation. [After S. M. Stanley, Earth System History. ]

5 FIGURE 9.21 Topography of the North American Cordillera in the western United States. Computer manipulation of digitized elevation data produced this color shaded-relief map in which the major geologic provinces of the area are clearly visible, as if illuminated by a light source low in the west. FIGURE 9.24 Much of the Cordillera of western North America has been formed by accretion over the past 200 million years. Wrangellia, for example, is a former island arc that was transported to its present location from 5000 km away in the Southern Hemisphere. [After D. R. Hutchison, Continental Margins. Oceanus 35 (Winter ): 34 44; modified from work of D. G. Howell, G. W. Moore, and T. J. Wiley.] Cordillera = mountain ranges Ma = megaannum or millions of years ago FIGURE 9.25 When plates bearing continents collide, the continental crust can break into multiple thrust fault sheets stacked one above the other. FIGURE 9.22 The interaction of the western coast of North America with the shrinking Farallon Plate as it was progressively subducted beneath the North American Plate, leaving the presentday Juan de Fuca and Cocos plates as small remnants. Large solid arrows show the present-day direction of relative movement between the Pacific and North American plates. [After W. J. Kious and R. I. Tilling, This Dynamic Earth: The Story of Plate Tectonics. Washington, D.C.: U.S. Geological Survey, 1996.] FIGURE 9.23 A global map of the continents, showing the major tectonic provinces. [W. Mooney/USGS.] Shields are areas of exposed basement rocks. FIGURE 9.26 The collision between India and Eurasia has produced many spectacular tectonic features, including large-scale faulting and uplift. [After P. Molnar and P. Tapponier, The Collision Between India and Eurasia. Scientific American (April 1977): 30.]

6 FIGURE 9.30 The Acasta gneiss in the Archean Slave craton of northwestern Canada, dated to 4.0 billion years ago, is the oldest rock formation so far discovered. It demonstrates that continental crust existed on Earth s surface at the beginning of the Archean eon. [Courtesy of Sam Bowring, Massachusetts Institute of Technology.] FIGURE 9.27 Paleogeographic reconstructions of the present North Atlantic region, showing the sequence of orogenic events that resulted from the assembly of Pangaea. (Ma, million years ago.) [Ronald C. Blakey, Northern Arizona University, Flagstaff.] FIGURE 9.28 The Wilson cycle describes the plate tectonic movements that open Jordan, and The Essential close Earth ocean 1e 2008 basins by W. H. Freeman and their Companyeffects on the continents. FIGURE 9.31 The universal tree of life shows how all organisms are related to one another. Organisms are subdivided into three great domains: the Bacteria, Archaea, and Eukaryota. These domains are all descended from a universal common ancestor. All three domains are dominated by microorganisms. Note that animals Jordan, The Essential appear Earth 1e at 2008 by the W. H. tip Freeman of and the Company eukaryote branch. (Ma, million years ago.) FIGURE 9.29 The ribbon of geologic time, showing some important events in the history of the continents. All numbers are ages in millions of years ago. FIGURE 9.32 (a) Abundant microfossils are well preserved in the 2.1-billionyear-old Gunflint formation of southern Ontario, Canada. [Images courtesy of H. J. Hofmann.]

7 FIGURE 9.32 (b) Early Archean (3.4 billion years old) stromatolites in the Warrawoona formation, Western Australia. The conical shapes suggest that the microbial mats that formed these rocks may have grown toward the sunlight. [Images courtesy of H J Hofmann ] FIGURE 9.35 Unusual sedimentary rocks and new, larger organisms mark the rise Jordan, of The oxygen Essential Earth in 1e the 2008 atmosphere by W. H. Freeman and between Company 2.7 billion and 2.1 billion years ago. (a) Banded iron formation. [Pan Terra.] FIGURE 9.33 Stromatolites are sedimentary features that result from the interaction of microbes with their environment. [Images from John Grotzinger.] FIGURE 9.35 Unusual sedimentary rocks and new, larger organisms mark the rise of oxygen in the atmosphere between 2.7 billion and 2.1 billion years ago. (b) These fossils of Grypania, a type of eukaryotic algae, are visible to the k d [C t f H J H f ] FIGURE 9.34 The ribbon of geologic time, showing major events in the history of life. (Ma, million years ago.) FIGURE 9.35 Unusual sedimentary rocks and new, larger organisms mark the rise of oxygen in the atmosphere between 2.7 billion and 2.1 billion years ago. (c) Jordan, Red The beds Essential Earth are 1e mostly 2008 by W. H. sandstones Freeman Company and shales partly cemented by iron oxide minerals. [John Grotzinger.]

8 FIGURE 9.36 Fossils that record the Cambrian explosion. Precambrian organisms such as Namacalathus (left ) were the first organisms to use calcite in making shells. These organisms became extinct at the Precambrian-Cambrian boundary, paving the way for a strange new group of organisms, including Hallucigenia (center ) and the more familiar trilobites (right). In each example, the fossils are shown on top and the reconstructed organism is shown on the bottom. [left, top: John Grotzinger; left, bottom: W. A. Watters; center, top: N ti l M f N t l Hi t /S ith i I tit ti t b tt Ch St di / Ph t R h FIGURE 9.39 The diversity of animal fossils reveals both mass extinctions and radiations. This graph shows the number of shelly animal families found in the fossil record during the last 600 million years; each family comprises many species. During a radiation, such as the Cambrian explosion, the number Jordan, of The new Essential animal Earth 1e families 2008 by W. increases. H. Freeman and During Companya mass extinction, such as occurred at the end of the Permian period, the number of families decreases. (Ma, million years ago.) From Physics Today, Nov FIGURE 9.37 Every major group of animals alive today originated during the early Cambrian radiation, also known as the Cambrian explosion Ma FIGURE 9.38 A fossilized animal embryo from the latest part of Precambrian time. Such fossils show that multicellular animals had evolved before the Precambrian- Cambrian boundary and are the ancestors of the animals that evolved during the Cambrian explosion. This cluster of cells is about 100 microns in diameter. [Courtesy Shuhai Xiao, Virginia Tech.] FIGURE 9.40 Knife marks a light-colored layer of clay containing both extraterrestrial materials and materials from local rocks at the Chicxulub impact site that accumulated in the Raton Basin of the southwestern United States following the asteroid impact that killed the dinosaurs ~65 Ma. Such deposits have been found worldwide. [From David Kring and Jordan, Daniel The Dura, Essential The Earth Day 1e the 2008 World by W. H. Burned, Freeman and Scientific Company American (December 2003): 104. December 2003 by Scientific American. All rights reserved.]

9 FIGURE 9.41 An artist s rendition of the Cretaceous-Tertiary scene after the asteroid impact at Chicxulub~65 Ma. [Alfred Kamajian.]