Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Earth Systems Chapter 2 © 2011 Pearson Education, Inc. What you will learn • Origin, structure, and character of the four Earth systems • Nature of the geologic time scale and the major periods of Earth history • Methods for determining the age of Earth materials • Rates of select Earth systems processes © 2011 Pearson Education, Inc. The Spheres • • • • • Atmosphere Hydrosphere Geosphere, and Biosphere All spheres interactive © 2011 Pearson Education, Inc. Earth’s Interactive Systems • • • • Much like the body with its many systems Transfers of energy between systems Open or closed system? Considering little change in amount of matter in or out of Earth’s realm—it functions as a closed system © 2011 Pearson Education, Inc. Origin of the Geosphere Birth of our planet—immense cloud of gas and interstellar debris called a nebula Figure 2.2a © 2011 Pearson Education, Inc. The Geosphere • • • • What is it? Solid Earth with its deep molten portions Is it a static or nonmoving mass? No, it’s dynamic and it has constant energy transfers that build mountain chains, create ocean basins, cause hazards such as volcanism, earthquakes, etc. • It also provides many benefits such as mineral wealth and energy resources © 2011 Pearson Education, Inc. Origin of the Geosphere 4.5 billion years before present (BYBP) immense cloud of gas and interstellar debris (nebula) began to collapse under its own gravity. Figure 2.2 The Formation of Earth and Our Solar System (a) Most stars, like the Sun, are born in clouds of gas and dust called nebulae. (b) The solar system was formed along with the Sun when part of a nebular cloud became dense enough to collapse. © 2011 Pearson Education, Inc. Geosphere Origin (cont.) • Denser and hotter center became the Sun • Dust, rocks, and gases swirling around Sun coalesced to form solar system planets • Rocky planets—Mercury, Venus, Earth, and Mars— formed closer to the Sun • Large gaseous planets—Jupiter, Saturn, Uranus, and Neptune—formed farther away © 2011 Pearson Education, Inc. The Geosphere Is Born Third planet from the Sun is Earth Figure 2.3 Location of the Planets Relative to the Sun The four small, rocky planets—Mercury, Venus, Earth, and Mars—are closer to the Sun than are the large gaseous ones—Jupiter, Saturn, Uranus, and Neptune. (Note that the distances are not drawn to scale. If they were, Earth would be almost 11 meters, or 36 ft, from the Sun, and Neptune about 330 meters, or 1080 ft.) © 2011 Pearson Education, Inc. Early Earth • Aggregation of nebular debris via many collisions of various sized particles • Heat generated by debris collisions, gravitational compression as the aggregated debris compacted, and by decay of radioactive elements such as Ur, Th, and K • Early Earth fairly uniform compositionally and partially molten © 2011 Pearson Education, Inc. Earth’s Moon • Probably formed after early Earth, half the size of present day Earth, was impacted by body roughly size of Mars—ejecta generated • Some ejected mass flung out from Earth formed the Moon © 2011 Pearson Education, Inc. Earth’s Early Surface a “Moonscape” • Views of the Moon not unlike early Earth Figure 2.4a Hints of Earth’s Early Appearance (a) Impact craters on the far side of the Moon show what Earth’s very early surface may have looked like. The Moon’s far side, the oldest surface on the Moon, preserves very old impact structures possibly formed between 4 and 4.5 billion years ago. © 2011 Pearson Education, Inc. Rare to Find Impact Evidence on Earth • Why? • Geospheric Change through Time Figure 2.4b Hints of Earth’s Early Appearance (b) Such scars are rare on today’s Earth. Most extraterrestrial objects burn up from friction as they pass through the atmosphere, and the craters formed by those that do reach the surface are soon erased by natural processes such as erosion. This crater, 1.2 kilometers (0.75 mi) across, formed in the Arizona desert when an asteroid 20 meters (65 ft) in diameter struck Earth. The impact occurred a mere 50,000 years ago—recently enough for the evidence to still be visible. © 2011 Pearson Education, Inc. Geospheric Compositional Structure • Earth began to differentiate into layers with varying compositions. • Denser elements such as Fe and Ni migrated to center of the planet • Less dense elements like Si, Al, O, K, and Na floated to surface • Once all elements moved and Earth differentiated, 3 distinct layers resulted—core, mantle, and crust Figure 2.5 Compositional Structure of the Geosphere (a) The geosphere’s internal structure formed early in Earth’s history. Its structure, based on composition, includes the inner and outer core, thick mantle, and thin crust. (b) The crust under continents is thicker and less dense than crust under the oceans. © 2011 Pearson Education, Inc. Earth’s Core—Two Parts • Solid inner core, 1200 kilometers (760 mi) thick, 1.7% of Earth’s mass; composition: Fe and Ni ( an alloy) • Liquid outer core, 2250 kilometers (1460 mi) thick, 30.8% of Earth’s mass (30.8%); composition Fe, some Ni, up to 10% lighter elements, perhaps O, S • Composition of core inferred from studies focusing on density, composition of iron-rich meteorites that are thought to be pieces of other planetary cores, and the manner seismic (earthquake) waves pass or don’t pass through it © 2011 Pearson Education, Inc. Earth’s Mantle—Below the Crust • Majority of Earth’s Interior is the mantle • 2850 km (1800 mi) thick, 67.1% of Earth’s total mass; composition somewhat variable but relatively homogeneous with mostly Mg and in decreasing abundance: Si, O, and Fe • Compositional knowledge draws on studies of Earth’s density, data from meteorites, and seismic waves and more information from upper mantle that has been brought to Earth’s surface (e.g., in volcanic eruptions) © 2011 Pearson Education, Inc. Earth’ Crust— the Thick and Thin of It • The outer thin skin of Earth is its crust • 80 km (50 mi) thick at its deepest point, contains rocks that can be examined at Earth’s surface Two different types of crust : A) Continental ~ 30 to 40 km (12 to 25 mi) thick (granite) B) Oceanic ~5 to 8 km (3 to 6 mi) thick (basalt) © 2011 Pearson Education, Inc. Comparison: Oceanic and Continental Crust Crust Type Oceanic Typical Thickness Oldest Age Dated 5-8 km (3-6 mi) 180 MY Basalt 4 BY Granite Continental 30-40 km (12-25 mi) © 2011 Pearson Education, Inc. Dominant Rock Defining Earth’s Interior • Abrupt changes in seismic wave velocities mark boundaries between various regions of the core, mantle, and crust • These include inner core, outer core, lower mantle, mantle transition zone, upper mantle, asthenosphere, and lithosphere Figure 2.6 The Physical Structure of the Geosphere Abrupt changes (discontinuities) in the velocity of seismic waves as they travel through the geosphere mark the boundaries between its physical subdivisions. © 2011 Pearson Education, Inc. Inner and Outer Core • Physically different inner core is solid and outer core is liquid • Very dense inner core is solid in spite of extremely high temperatures because of the very high pressures at Earth’s center • Outer core is liquid because pressures are slightly lower in this region, but temps are still high, exceeding melting point of iron. Outer core is liquid because it drastically slows down fast seismic waves (see Figure 2-6a) and other seismic waves cannot pass through it at all © 2011 Pearson Education, Inc. Lower Mantle and Mantle Transition • Solid rock lower mantle occurs from 2900 km (1800 mi) to 660 km (410 mi) depth, gradually increases in density (and seismic wave velocity) downward toward the boundary with molten outer core • Although upper and lower mantle rocks are similar in composition, the higher P in the lower mantle makes minerals there different (denser than) those in the upper mantle • Mantle transition zone is between 660 km (410 mi) and 410 km (250 mi) deep © 2011 Pearson Education, Inc. Upper Mantle and the Moho • Upper mantle lies above the transition zone and extends upward to base of the crust • Defined by an abrupt increase in seismic wave velocities as waves pass downward through it; was one of the first internal geosphere boundaries to be recognized • Mohorovićić discontinuity or just Moho marks the boundary © 2011 Pearson Education, Inc. Asthenosphere and Lithosphere • Brittle uppermost mantle and crust comprise the lithosphere (tectonic plates) • Weak zone (non-brittle) upper mantle just below lithosphere is the asthenosphere • Asthenosphere and lithosphere also differentiated based on seismic velocities (Fig. 2.6) © 2011 Pearson Education, Inc. Earth’s Atmosphere • Gases that surround the geosphere (air) comprise the atmosphere • Atmosphere extends from Earth’s surface upward for many hundreds of km; no distinct top, gradually becomes less dense and merges with empty space • Also includes gases that fill voids in near-surface geosphere • The atmosphere is Earth’s most dynamic system and is the vessel for life-dependent gases such as oxygen and carbon dioxide © 2011 Pearson Education, Inc. Origin of the Atmosphere—the First Atmosphere • Gases were part of nebular cloud that condensed to form our solar system • Gases common in nebular clouds, and in outer gaseous planets include hydrogen (H), helium (He), methane (CH4), and ammonia (NH3); Earth’s first atmosphere probably included such gases • Prior to Earth’s complete differentiation of the geosphere and while still very hot, perhaps before a liquid outer core was fully developed and before complete aggregation, gravity could not hold these gases closely around Earth; the first atmosphere is therefore inferred to have left Earth © 2011 Pearson Education, Inc. Earth’s Second Atmosphere • Volatiles (easily vaporized elements or compounds) were also present in nebular material that formed the initial solid Earth. Such volatile components included hydrogen (H), carbon (C), and nitrogen (N) as well as compounds formed from these elements such as water (H2O), carbon dioxide (CO2), and ammonia (NH3) • These elements and compounds are characteristic of primitive meteorites called carbonaceous chondrites thought to be representative of the nebular cloud composition that condensed to form the solar system • Thus, materials in the early solid Earth that contained volatile components if vaporized could have contributed to the formation of Earth’s atmosphere © 2011 Pearson Education, Inc. Outgassing Forming the Second Atmosphere • What dominant process was active during the first 1 billion years of Earth’s existence to form the second atmosphere? • Outgassing—via volcanism which transferred volatile components from the interior geosphere to Earth’s surface and atmosphere • Volatiles in molten rock (magma) erupted from volcanoes in the form of lava (surface) © 2011 Pearson Education, Inc. Volcanism—Clues to Outgassing Forming Earth’s Second Atmosphere • An estimate of what early volcanism released to the atmosphere can be obtained by studying outgassing of modern volcanoes like those in Hawaii • Present-day volcanic eruptions release water vapor (H2O), carbon dioxide (CO2), nitrogen, and sulfur compounds (especially sulfur dioxide, SO2) to the atmosphere © 2011 Pearson Education, Inc. Figure 2.8 Outgassing Studying the release of gases by modern volcanoes, such as Mt. Etna in Sicily, shown here, helps us to understand how Earth’s early atmosphere was formed. Volcanism—Clues to Outgassing Forming Earth’s Second Atmosphere • Atmosphere created by outgassing in Earth’s early history is thought to have contained mostly water vapor and carbon dioxide along with nitrogen, sulfur compounds, some hydrogen, and compounds formed from the reactions of these gases, such as ammonia and methane • Carbon dioxide, methane, and water vapor are gases that cause the atmosphere’s temperature to rise = greenhouse gases. Climate during the time of the second atmosphere was very warm—no polar ice caps, no liquid water or free oxygen—life as we know it today didn’t exist in the 1st BY (4.5 to 3.5 BYBP) © 2011 Pearson Education, Inc. The Third Atmosphere—Today’s Air © 2011 Pearson Education, Inc. Processes Dominant for Forming Third Atmosphere • Today’s atmosphere (Table 2–1) is called Earth’s third atmosphere • Big changes needed to transform Earth’s second atmosphere to make the third atmosphere • Large volumes of H20 and CO2 had to be removed and a lot of N and O needed to be added to evolve into the third atmosphere • How did this come about? • Excess H20 went to the hydrosphere—mostly in oceans, but also as rivers, lakes, and streams. By 3.5 BYBP, Earth’s oceans had formed from water that precipitated from the second atmosphere as the geosphere began to cool © 2011 Pearson Education, Inc. Third Atmosphere’s Link to Geosphere and Oceans—Rock and Mineral Products • Once the world ocean existed, CO2 from atmosphere began to dissolve in its waters • Dissolved CO2 in turn reacted with Ca to form solid calcium carbonate (CaCO3), which started to precipitate and accumulate on the seafloor • Because many organisms incorporate CaCO3 into their shells and skeletons that then accumulate on the seafloor, the rate of precipitation increased once living plants and animals came upon the scene Figure 2.9 Calcium Carbonate, an Important Carbon Sink Many organisms incorporate calcium carbonate into their shells and skeletons (a), which then accumulate on the ocean floor (b). During Earth’s history, much of this material has been compressed into rock, like the famous white limestone cliffs that overlook the English Channel (c), thus becoming a major geosphere sink for carbon. © 2011 Pearson Education, Inc. Third Atmosphere’s Link to Geosphere and Oceans—Rock and Mineral Products • Most seafloor CaCO3 accumulations gradually turn into rocks and become part of the geosphere (mostly CaCO3 rock as limestone) • The geosphere is the world’s largest carbon reservoir and a global sink for CO2; concentration of CO2 in the atmosphere slowly decreased as CO2 was transferred through the oceans to the geosphere © 2011 Pearson Education, Inc. Nitrogen and Oxygen in the Modern Atomosphere • Nitrogen degassed significantly to provide nearly 80% of our air as we now know it • Even though nitrogen increased during Earth’s early history there was still no free oxygen. Origin of the atmosphere’s free oxygen is tied to changes in the biosphere © 2011 Pearson Education, Inc. Biosphere’s Role in Production of Free Oxygen for the Third Atmosphere Figure 2.10a The Atmosphere’s Oxygen Came from Photosynthetic Organisms Earth’s first free oxygen, produced by photosynthetic cyanobacteria (a), was trapped in banded iron formations. • Some of the earliest life forms on Earth were microorganisms called cyanobacteria that are photosynthetic • Photosynthetic organisms use sunlight to convert CO2 and H20 into food and oxygen, a process called photosynthesis • Cyanobacteria started making oxygen about 3.5 BYBP, but oxygen didn’t increase in Earth’s atmosphere for another billion years • Why was this the case? © 2011 Pearson Education, Inc. Increases in Atmospheric Oxygen • Finally, about 2 billion years ago (about 1.5 billion years after cyanobacteria started generating oxygen), most of the material that readily reacted with the atmosphere’s early oxygen was used up • Oxygen concentration of the atmosphere began to slowly increase as photosynthetic organisms increased in abundance • About 500 MYBP land plants first appeared and the atmosphere’s oxygen level had become approximately what it is today; almost all animals must breath in oxygen to survive, thus oxygen levels are thought to have caused a tremendous expansion of the biosphere’s diversity at this time (called the Cambrian Period Explosion) © 2011 Pearson Education, Inc. BIFs—Storers of Early Produced Oxygen • So what was the sink for early produced oxygen? • The answer is in the rocks. Newly formed oxygen reacted with abundant Fe and S on Earth’s surface and dissolved into the early ocean • Chemical reactions formed solid minerals, especially iron oxides that accumulated in sediments to become rocks known as banded iron formations (BIFs). • BIFs are sinks where Earth’s early oxygen is stored today Figure 2.10b The Atmosphere’s Oxygen Came from Photosynthetic Organisms (b), a sink for early oxygen in the geosphere. © 2011 Pearson Education, Inc. Compositional Structure of the Atmosphere • Atmosphere’s overall thickness is typically 480 km (300 mi) or more • Atmosphere has two layers that are defined by compositional variations— homosphere and heterosphere Figure 2.11 The Structure of the Atmosphere Variations in composition and temperature define the atmosphere’s structure. Note that the heterosphere, from 80 km to about 480 km, is not shown in full. The region above the heterosphere, where Earth’s atmosphere merges with outer space, is sometimes called the exosphere. © 2011 Pearson Education, Inc. Temperature Structure of the Atmosphere • Solar radiation interacting with Earth’s surface and atmosphere produce temperature variations that define four atmospheric layers • The four layers in ascending order: troposphere, stratosphere, mesosphere, and thermosphere © 2011 Pearson Education, Inc. Troposphere • Troposphere’s thickness varies from 7 km (4 mi) near poles to 17 km (11 mi) near the equator; temp ∆ in the troposphere is related to the heating of Earth’s surface by solar radiation— cools upward until constant at tropopause • Troposphere is most dynamic place within the atmosphere • Highly significant—where life lives, weather occurs; about half of the mass atmosphere is in the lower 5 km (3 mi) of the troposphere © 2011 Pearson Education, Inc. Stratosphere • Temps upward through the stratosphere Higher temps of the stratosphere vs. those of the underlying troposphere prevent air from rising and crossing their boundary zone, the tropopause • Top of the stratosphere is marked by a temp ; this boundary, called the stratopause, is at an altitude of ~50 km (30 mi) from Earth’s surface © 2011 Pearson Education, Inc. Stratospheric Ozone—the Great Protector of the Biosphere • Temp ∆s through stratosphere are caused by the interaction of incoming solar radiation and oxygen • Common oxygen molecules (O2) absorb short-wavelength, ultraviolet (UV) radiation in the upper stratosphere and split apart into highly reactive oxygen atoms (O) • These single O atoms then bond with O2 molecules to form ozone (O3), oxygen molecules that contain three oxygen atoms • Ozone forms slowly in the stratosphere and can be destroyed by reactions with sunlight and other atmosphere components • Ozone is concentrated (albeit in small amounts) in the lower stratosphere where it is not destroyed as rapidly—part of the stratosphere that is referred to as the ozone layer, a great protector for screening UV and other harmful radiation for all life on Earth © 2011 Pearson Education, Inc. Stratosphere (cont.)— characteristics Figure 2.12 The View from the Stratosphere This photo is taken from the cloudless stratosphere, looking down on the clouds in the troposphere below. • Upward temp through stratosphere prevents air from rising within it and causes it to be internally stratified • Small quantities of water vapor and stratified character of the stratosphere make it a generally cloudless part of the atmosphere; winds ~ parallel to Earth’s surface • Observable as clear area above clouds in troposphere © 2011 Pearson Education, Inc. The Mesosphere • Above the stratosphere, from ~ 50 to 80 km (30 to 50 mi) in altitude • Temps upward through the mesosphere to a boundary zone (mesopause) where the lowest temps in the atmosphere are present • Temps upward through the mesosphere reflect less concentration of gas molecules that absorb UV radiation; also related to presence of small amounts of CO2; CO2 absorbs and reradiates solar energy, but there are so few other gas molecules around to absorb this energy it is lost to space; this cools the mesosphere, the opposite of the effect CO2 has in the troposphere; there, CO2 acts as a greenhouse gas by trapping heat energy from Earth’s surface and transferring it to other gas molecules in the atmosphere © 2011 Pearson Education, Inc. The Mesosphere (cont.) • Although the concentration of gas molecules in the mesosphere is low, there are still enough of them to have some significant effects—friction with the few gas molecules present causes meteoroids to heat up, observable as shooting stars, and most burn up in the mesophere • Exosphere—beyond mesophere (where satellites travel)—atmosphere/space boundary © 2011 Pearson Education, Inc. The Thermosphere • Outer atmospheric layer above the mesosphere. Temps and air molecules upward through the thermosphere as it gradually merges into space at altitudes of 480 km (300 mi) or higher • Compositionally defined the same as the heterosphere; temperature upward in thermosphere is due to interaction of intense solar radiation with the increasingly sparse gas molecules and atoms (mostly nitrogen and oxygen) © 2011 Pearson Education, Inc. The Thermosphere (cont.) • In cases where solar radiation is intense, it can change gas molecules into charged particles (ions); because a lot of the ionization of the atmosphere happens in the thermosphere =the ionosphere • Charged particles colliding in the thermosphere produce the northern lights (aurora borealis) and southern lights (aurora australis)—moving sheets and wisps of colored light visible at high latitudes on clear nights Figure 2.13 Northern Lights on a Clear Winter Night Ions, formed by the collision of fastmoving charged particles ejected from the Sun with atoms of gas in the atmosphere, create the polar auroras. © 2011 Pearson Education, Inc. Earth’s Hydrosphere • Directly connected between solar energy and Earth system processes • Consists of all water in oceans, on land in streams and lakes, in glaciers and other accumulations of ice, in the atmosphere and underground • “The Water Planet”—Water covers 71% of Earth’s surface • Earth uniquely positioned in solar system so that water exists in all three phases —solid (ice), liquid, and gas (water vapor) © 2011 Pearson Education, Inc. Origin of Earth’s Water • How did Earth become so dominated by water on its surface? • Water was part of the original nebular debris that coalesced, forming Earth. Other contributions were from volcanic outgassing that released volatiles including water vapor, during formation of Earth’s second atmosphere, and possibly from comets slamming into Earth • Upon early Earth’s more complete cooling, water vapor in the second atmosphere condensed and was able to remain liquid on Earth’s surface • Oldest known rocks that formed from ocean sediments are 3.8 BY old. These rocks confirm some compositional characteristics of the second atmosphere and convey to us that oceans were present, meaning the hydrosphere was complete at that time © 2011 Pearson Education, Inc. The Hydrosphere’s Reservoirs • Unlike the atmosphere or geosphere, the hydrosphere lacks an internal structure but possesses distinctive reservoirs • The world’s oceans are the largest reservoir in the hydrosphere (97% of Earth’s water) Figure 2.14 The Hydrosphere’s Reservoirs More than 97% of the hydrosphere consists of saltwater in the oceans. Of the fresh (nonsalty) water, almost 69% is frozen in glaciers, ice caps, and ice sheets, and 30% is underground. The rest—only 1.3%—can be found in many small reservoirs such as streams, rivers, and lakes. This fresh, liquid surface water thus makes up only about 0.036% of all the water on Earth. © 2011 Pearson Education, Inc. The Hydrosphere’s Reservoirs (cont.) • Freshwater—only 2.8% of Earth’s water; however, only a small amount of that water is readily available for human use • Freshwater distributed in lakes, streams, rivers, underground, and in the atmosphere but these are small compared to Earth’s accumulations of solid freshwater in glaciers, ice caps, and ice sheets (up to 68.6% of Earth’s freshwater is ice) © 2011 Pearson Education, Inc. The World Ocean • Contains 97.2% of all the water in the hydrosphere—a continuous body of water that covers 71% of Earth’s surface. Over 3 kilometers (1.9 mi) deep in over half this area • Internal structure, defined by variations in salinity and temperature but as one big reservoir it has only two parts • Upper layer—about 200 meters (700 ft) thick, that is warmed by the sun and mixed by the waves and currents created by surface winds © 2011 Pearson Education, Inc. The World Ocean (cont.) • Lower layer—at depths below about 1000 meters (3000 ft), solar radiation has little effect, and water temps are low, commonly in the 0o to 4o C (32o to 39o F) range. Water can still be in motion because salinity and temp differences change the water’s density. Denser (colder and saltier) water sinks and slowly flows through the deep ocean and back to the surface in a global circulation • The world ocean is a major influence on global climate. Because of water’s great specific heat capacity compared to air of the atmosphere Figure 2.15 Movement of Water in the World Ocean Currents, driven by winds and density differences, move water in the hydrosphere’s largest reservoir, the oceans. © 2011 Pearson Education, Inc. Glaciers, Ice Caps, and Ice Sheets • If snow accumulation > melting of snow then glaciers can form • Seasonal conditions that enable glaciers to form exist at high elevations in mountains and at high latitudes near the north and south poles • Mountain (alpine) glaciers vary from small patches to large rivers of ice that slowly flow downslope; ice movement carves many landforms that are distinctive of glacial regions Figure 2.16 Glaciers in Southern Alaska Glaciers carve deep valleys, move broken and ground-up rock along their base and margins, and coalesce into large masses of ice. These glaciers flow from an ice cap in the coastal mountains of southern Alaska. © 2011 Pearson Education, Inc. Glaciers, Ice Caps, and Ice Sheets (cont.) • Where glaciers coalesce and cover larger areas they become ice caps (less than 50,000 square km, or 19,000 mi2) and ice sheets (greater than square 50,000 square kilometers) • Modern world—ice covers about 10% of Earth’s land area; most in ice sheets on Greenland and one on Antarctica © 2011 Pearson Education, Inc. The Water Cycle Figure 2.17 The Water Cycle The water cycle transfers matter and energy among Earth systems. • Hydrosphere interacts with other Earth systems in the water cycle; cycle transfers a prized resource among its reservoirs (oceans, atmosphere, on and under land) • Atmosphere over the oceans is a key part of the water cycle; ~ 86% of its water vapor obtained through evaporation from seas • When air rises, it cools, causing water vapor to turn into tiny droplets to form clouds. Where air temperature falls, as when air rises along mountains, the liquid water droplets condense and fall to Earth’s surface. Precipitation of rain, snow, or ice (hail) transfers water to the land © 2011 Pearson Education, Inc. Water Cycle (cont.) • Precipitation transfers water to 3 reservoirs on land— (1) ice; (2) surface water and (3) groundwater • Rivers and streams carry water back to the oceans; groundwater migrates back to the oceans in many coastal settings • Water is used by plants, animals, and people, but it is stored only temporarily—it cycles back to the atmosphere through respiration and transpiration • Earth system processes and interactions in the water cycle involve energy and matter transfer between atmosphere, biosphere, and geosphere © 2011 Pearson Education, Inc. Earth’s Biosphere • Consists of all life on Earth—large and small • From molecular level to vast, complex ecosystems, significant interaction with various Earth spheres • Produces food, role in carbon cycle, a pollution filter, a capturer of energy, aids in soil development, etc. • What started evolution to make life so diverse? © 2011 Pearson Education, Inc. Earth’s Biosphere (cont.) • Chemical and fossil (paleontological) evidence in ancient rocks provides insight into the origin of life on Earth; fossils are remains or evidence of former life preserved in rocks • Example of fossils (Figure 2-18)—fossils can be actual remains, or just imprints of an organism or its hard parts, such as shells or dinosaur bones © 2011 Pearson Education, Inc. Earth’s Biosphere (cont.) Figure 2.18 Fossilized Remains of Former Life Fossils are remains or imprints of organisms, preserved in rocks. (a) Ammonites, members of a group of shelled animals related to modern squid and octopi, survived for some 350 million years. The one who left these remains floated in the ocean about 200 million years ago. (b) These fossilized bones belonged to a relative of the famous T. rex. Dinosaurs of this group lived from 170 to 65 million years ago. (c) Seed plants like the ones that left these impressions grew in Europe and North America some 280–300 million years ago. © 2011 Pearson Education, Inc. Some of the Oldest Fossils • Bacteria—oldest fossils on Earth. Traces of thread-like, singlecelled organisms have been preserved in 3.2-BY old sedimentary rocks in Australia • Stromatolites are fossils found in even older rocks (as much as 3.5 BY). These are structures built from layer after layer of muddy sediment trapped by mats of bacteria (Figure 2-19a). Descendants of stromatolite-forming bacteria still inhabit some coastal environments. • Cyanobacteria, the first photosynthetic organisms, live in stromatolites today, but it is unknown if bacteria that lived in very old stromatolites were photosynthetic Figure 2.19a Stromatolites Stromatolites—layers of muddy sediment trapped by films of microorganisms—are some of Earth’s oldest fossils (a) © 2011 Pearson Education, Inc. Early Evolutionary Thought and Fossils • In 17th century Danish anatomist Nicolas Steno (also known as Neils Stenson)—recognized “tongue stones” were fossilized shark teeth as he compared modern shark anatomy to the rock record—established that that fossil represented former life in former seas © 2011 Pearson Education, Inc. Early Evolutionary Thought and Fossils (cont.) By the end of 18th century, fossils became focus of naturalist studies. Vertebrate fossils were the specialty of Georges Cuvier and invertebrate fossils were the specialty of Jean Baptiste Lamarck, both members of the French Museum of Natural History. By 1798 Cuvier showed that vertebrate fossils represented species that no longer existed—for example, that mammoths differed from living elephants and that mammoths were extinct. Lamarck recognized life’s complexity and change through time. Figure 2.20 An Extinct Vertebrate and a Modern Relative From the study of their fossil remains, Cuvier demonstrated that mammoths (a), shown here in an artist’s reconstruction, were an extinct species, different from modern elephants (b). © 2011 Pearson Education, Inc. Darwin and Wallace—Evolutionary Giants • Charles Darwin and Alfred Russel Wallace— investigated how life changed over time by the process of natural selection • Wallace studied the distribution of species (biogeography), developed his own ideas about natural selection • Darwin and Wallace communicated, shared specimens, and jointly presented their ideas on the subject at a scientific meeting in 1858 © 2011 Pearson Education, Inc. Darwin and Wallace—Evolutionary Giants (cont.) Darwin published Origin of the Species in 1859, while Wallace continued his biogeography studies. Darwin’s best examples came from his early studies as a naturalist on a cruise of the H.MS. Beagle. Figure 2.21 Darwin’s Journey As a young man, Charles Darwin sailed around the world as naturalist on H.M.S. Beagle. Much of the voyage, which lasted nearly five years, was spent exploring the coasts of South America. Darwin made many of the observations that inspired his theory of evolution by natural selection in the Galápagos Islands. In that isolated region, a unique and distinctive array of species evolved as plants and animals have adapted to the varied environments on the different islands. © 2011 Pearson Education, Inc. Darwin’s Galapagos Island Studies Figure 2.22 Seven of Darwin’s Finches Darwin discovered an amazing variety of closely related species on the Galápagos Islands in 1835. Thirteen species of finches had evolved different characteristics, especially of their beaks, to adapt to available food on the different islands. • Via anatomical comparisions Darwin studied related but different species of finches on the Galápagos Islands • He proposed that natural selection explained how these and other species evolved © 2011 Pearson Education, Inc. Mass Extinctions through Geologic Time • Difficult times for the biosphere are times when a large number of species became extinct. These are called mass extinctions • At least 5 major extinctions during the last 540 million years • Most recent and most famous mass extinction ~ 65 MYBP when dinosaurs perished Figure 2.23 Mass Extinctions Mass extinctions indicate very stressful times for the biosphere. There have been five major mass extinctions during the last 540 million years. © 2011 Pearson Education, Inc. Death of the Dinosaurs • Scientists think this mass extinction resulted from the impact of a large asteroid on what is now the Yucatan Peninsula of Mexico • Earth was not a closed system 65 million years ago! • Impact of this large asteroid darkened the skies with dust and caused severe global Figure 2.24 The End of the Dinosaurs climate changes that were just The dinosaurs died out in a mass extinction that occurred 65 million years ago. The cause of this event is thought to have been the too much for the dinosaurs— impact of an asteroid, shown here in an artist’s depiction (a), in the Gulf of Mexico just off the coast of Mexico’s Yucatan Peninsula (b). and many other species—to The asteroid was probably at least 10 kilometers (6 mi) in diameter. Its impact released more energy than a million hydrogen bombs handle and blasted a crater greater than 160 kilometers (100 mi) in diameter, now buried under thick layers of sediment. © 2011 Pearson Education, Inc. The Passenger Pigeon—a Recent Extinction Example Figure 2.25 Martha: The Last Passenger Pigeon • The passenger pigeon is probably the only species for which we know the exact date of its extinction. The last known passenger pigeon, Martha, died at 1:00 p.m., September 1, 1914, in the Cincinnati Zoological Garden • Fate of the passenger pigeon was determined years before; passenger pigeons had a problem; they were easy to catch and good to eat © 2011 Pearson Education, Inc. Understanding Geologic Time and Earth History • Earth’s history to be understood must be placed into the context of geologic time • Scientists determine both relative and absolute ages of events in Earth’s history • Examples: age of glacial advance, a volcano erupting, an ocean basin forming, a mountain belt forming • Age determination aids in our understanding rates of geologic processes and Earth system interactions © 2011 Pearson Education, Inc. Relative Time Tools • Being able to tell that one strata or event is older or younger in comparison to another is referred to as relative dating • A number of early scientists made observations and developed relative time dating tools or established principles that we still use today to aid in discerning Earth history © 2011 Pearson Education, Inc. Relative Time Tools—Basic Principles • Nicholas Steno’s Law of Superposition • William “Strata” Smith’s fossil succession idea • Combination of relative and eventually absolute time concepts helped to establish the geologic time scale © 2011 Pearson Education, Inc. Geologic Time Scale Figure 2-27 The Geologic Time Scale The geologic time scale summarizes Earth’s geologic history as determined from studies of rocks, fossils, and their relative ages. Radiometric dating has enabled the absolute ages of geologic events to be determined and added to the time scale. (Note that the time intervals are not drawn to scale.) © 2011 Pearson Education, Inc. SUMMARY • Earth’s position in the solar system is perfect for evolution of three physical systems—permits wide range of life forms to be sustained and evolve • Globally defined physical systems include the: • Geosphere • Hydrosphere, and • Atmosphere • Physical systems interact to provide niches for all of the biosphere, including humans © 2011 Pearson Education, Inc. SUMMARY (cont.) • Geosphere—differentiated into core, mantle, and two types of crust— continental and oceanic • State of matter of a differentiated Earth— detected indirectly by seismic waves as solid inner core, liquid outer core, mantle, asthenosphere, and crust © 2011 Pearson Education, Inc.