Geology Chapt 3
SL has risen and fallen many times over Earth's history
+/- 300 meters during the Phanerozoic Transgression (SL rise): shorelines move landward Regression (SL fall): shorelines move seaward Sedimentary rocks preserve evidence of sea-level change. Sea-level cycles are bounded by unconformities.
The rock cycle—there are three types of rock
Igneous—cooled from a mel. Sedimentary—made of weathered and eroded materials Metamorphic—rocks altered by heat and pressure
The supercontinent cycle
Plate tectonics drives continental movement. Ocean basins open and close. Continental landmasses collide and rift apart. Supercontinents (like Pangaea) have formed several times.
The hydrologic cycle
Water moves between reservoirs on or near Earth's surface. Biological: All living organisms Physical: Oceans Atmosphere Surface water Ground water Glaciers Soil moisture
. What factors explain short- term climatic change?
(a) The abundance of sunspots (cool spots on the surface of the Sun, which may represent magnetic storms) varies over the course of a de cade or so and may affect total incident solar radiation. (b) Earth's orbital shape, magnitude of tilt, and direction of tilt vary over Milankovitch cycles with periods in the tens of thousands of years. These parameters influence whether glaciers are likely to descend over the continents or melt. (c) Earth's albedo can be increased by an increase in aerosols (such as volcanic ash), cloud cover, and surface ice, or the spread of deserts and grasslands over land that was once forested. (d) Ocean currents may change course, altering the hydrologic system that brings warmth to some areas and cold, dry conditions to others.
. What are the possible causes of long- term climate change?
(a) The sizes and positions of the continents are important; in order for large continental glaciers to grow, it is favorable to have large continents in regions near the poles; small continents bathed in tropical oceans favor greenhouse conditions. (b) Volcanoes emit carbon dioxide, which adds to the greenhouse effect. (c) Uplifted areas are sites of intense weathering, and chemical weathering draws down atmospheric carbon dioxide. (d) Limestone, coal, organic- rich shale, and oil contain carbon, so when produced in vast quantities and buried, they keep carbon from reaching the atmosphere as carbon dioxide. Carbon burial is a check on the greenhouse effect.
• Carbon is returned to the atmosphere (aka release)
- Biotic respiration creates CO2 from organic matter. - Rapid oxidation (burning) of organic matter creates CO2. - Metamorphism of carbonate rocks liberates CO2. - Degassing removes dissolved CO2 from water.
• Carbon may be stored for long periods of time (aka sequestration
- Limestones - Fossil fuels (coal and oil) - Organic shales - Methane hydrates
• Paleoclimatic evidence
- Paleontological—faunal assemblages reflect climate. • Assemblage changes record climatic shifts. - Pollen in pond sediments • Spruce (colder) versus pine (warmer) • Trees (colder, drier) versus grasses (warmer, wetter)
Hadean Eon (Pre-Cambrian)
- Planet cooled, the first oceans formed as rain from the skies. The Earth formed about 4.57 billion years ago. For part of the first 600 million years, the Hadean Eon, the planet was so hot that its surface was a magma ocean.
Steps to fossilization
1. An organism dies 2. The remains get buried quickly by sediment. The soft parts decay. 3. With time, the hard parts get replaced with minerals. The sediment lay gets buried deeper and is compacted and cemented to form Sedimentary Rock. 4. The fossil is later exposed through erosion. Major bias in the fossil record - hard parts are preferentially preserved.
What might have caused the mass extinction at the end of the Paleozoic?
: At this time, the Siberian traps formed. These flood basalts represent a massive volcanic eruption that could have triggered drastic and sudden environmental changes.
. Describe how CO2-induced global warming takes place, and how humans may be responsible. What effects might global warming have on the Earth System?
: Carbon dioxide (CO2) is called a greenhouse gas because, in analogy the glass of a green house, it allows solar radiation to reach Earth, but traps in the infrared radiation that the Earth emits to outer space. Because of its relative abundance, CO2 is the most significant of the greenhouse gases in the atmosphere. Humans are likely responsible for increased atmospheric CO2 (and resultant greenhouse warming) because the burning of fossil fuels emits carbon dioxide into the atmosphere, and the increase in atmospheric carbon dioxide over the past two centuries is too rapid to have been caused by geologic processes. Effects of global warming on the Earth System include sea- level rise, the breakup of polar ice shelves, the melting of glaciers, a reduction in sea- ice formation, shifts in patterns of precipitation and climate belts, changes in the range distributions of animals, imperilment of polar wildlife, stronger storms (including hurricanes), and disruption of oceanic currents (which may bring further climatic change, including cooling of high latitudes).
Give some examples of events that cause catastrophic change.
: Comet or asteroid impact, explosive or hyperactive volcanism, and sudden episodes of global warming or cooling can cause catastrophic change.
Why are there no whole rocks on Earth that yield isotropic dates older than 4 billion years?
: Earth is a geologically active planet. Subduction, erosion, metamorphism, and melting destroy rocks.
What may have caused the flooding of the continents during the Cretaceous Period?
: Rapid Cretaceous rates of submarine volcanism thickened the mid- ocean ridges and produced numerous hot spots, which displaced water onto the continents. Additionally, glacial ice could not accumulate anywhere on Earth in the associated greenhouse warmth.
Cenozoic life evolution
After the K-T boundary, plant life recovered. Forests of angiosperms and gymnosperms reappeared. The 1st grasses appeared in the middle Cenozoic. Dinosaur descendants (birds) diversified and spread. The Cenozoic is known as the age of mammals. Mammals rapidly diversified to fill vacated niches. By the mid-Cenozoic, huge mammals appeared (Woolly mammoths. Giant beavers, Ground sloths). Late Cenozoic, human ancestors 1st appeared.
Paleozoic
Ancient life. As the Paleozoic Era began, rifting yielded several separate continents. Sea level rose and fell, depositing sequences of strata in continental interiors. Continents coalesced again, to form another supercontinent, Pangaea. Early Paleozoic evolution produced many invertebrates with shells, and jawless fish. Land plants and insects appeared in the middle Paleozoic, and by the end of the eon, there were land reptiles and gymnosperm trees.
How does carbon cycle through the various Earth systems?
Carbon dioxide in the atmosphere dissolves in the ocean to form carbonate (and bicarbonate) ions. These ions are removed by a variety of organisms to produce calcium carbonate skeletons, which collect as fragments and grains at the bottom after the organisms die, perhaps later lithifying to form limestone. Carbon dioxide can also be removed, either directly from the atmosphere or from solution in the ocean, through biogenic photosynthesis, to produce organic carbon. Organic carbon may become incorporated into the rock record in shale, oil, and coal, but some may be released to the environment through animal respiration and flatulence. Weathering of silicate rocks removes atmospheric carbon dioxide, producing bicarbonate ions. Burning fossil fuels releases atmospheric carbon dioxide, as do volcanic eruptions.
Cretaceous paleogeography
Climate continued to warm. Seas flooded the continents. An ocean connected the Gulf of Mexico to the Arctic.
. What are the major types of organisms that appeared during the Paleozoic?
Conodonts, trilobites, mollusks, brachiopods, and echinoderms.
What life forms appeared during the Mesozoic?
Dinosaurs, mammals, birds, large swimming reptiles, and pterosaurs are a few examples.
How have the Earth's crust and atmosphere changed since they first formed?
Early in its history, Earth was hot enough to melt iron. Molten iron migrated toward the center of Earth, differentiating the core from the mantle- like exterior. The first crust was a thin skin, which was subjected to subduction and remelting. As Earth cooled, subducted material from the surface no longer completely melted, and partial melting produced magmas that were more silicic than the ultramafic chemistry of the initial mantle and crust. Basaltic magmas formed oceanic crust, and intermediate and silicic magmas crystallized to form buoyant continental crust. Earth's primordial atmosphere of hydrogen and helium was likely lost to space; a secondary atmosphere dominated by the volcanic gases water vapor, carbon dioxide, sulfur dioxide, and nitrogen lost the fi rst three of these to the oceans, which formed as Earth cooled. Oxygen was added by biotic photosynthesis to the remnant nitrogen, and these two gases dominate the modern atmosphere.
Give some examples of how humans have changed Earth.
Extraction of rock and groundwater; overhunting and overfishing; destruction of forests and grasslands; and pollution of the air, streams, and oceans have led to increased mass wasting, famine, high rates of biotic extinction, acid rain, smog, a hole in the ozone layer, climate change, and so on.
What evidence do we have that Earth nearly froze over twice during the Proterozoic Eon?
Glacial deposits have been found in sedimentary rocks representing sea- level environments along the paleoequator.
What processes control the rise and fall of sea level on Earth?
Global sea level is primarily controlled by the volume of glacial ice on continents, which is inversely related to sea level, and the volume of mid- ocean- ridge volcanoes, which has a positive effect. At times of rapidly moving plates (abundant mid- ocean- ridge volcanism), excess carbon dioxide leads to a stronger greenhouse effect, warming the ocean and melting glaciers (if any are present), which raises sea level by adding ocean water. Rapid volcanism also produces thick mid- ocean- ridge volcanic chains, which displace water onto the continents. Conversely, when sea- fl oor- spreading rates are low, ridge volume is small, and the atmospheric level of carbon dioxide is also low. The resultant reduction in the greenhouse effect favors the formation of continental glaciers, freezing out water that is now unavailable to the ocean.
Contrast ice house and green house conditions.
Greenhouse climate is warmer than that of today (especially at the poles) and is characterized by a high atmospheric concentration of carbon dioxide and a relatively high sea level, with no continental glaciers at the poles. In contrast, ice house conditions are colder, with permanent ice present at the poles and relatively low levels of atmospheric carbon dioxide and low sea level.
Greenhouse effect
H2O, CO2, and CH4 in Earth's atmosphere absorb thermal energy emitted by the earth and reradiate it, warming the lower atmosphere.
Why do we use the term Earth System to describe the components of processes operating on this planet?
Many biotic and abiotic processes are complexly interrelated.
Mesozoic
Middle life. In the Mesozoic Era, Pangaea broke apart, and the Atlantic Ocean formed. Convergent boundary tectonics dominated along the western margin of North America. Dinosaurs became prominent land animals through the Mesozoic Era. During the Cretaceous Period, the continents flooded. Angiosperms appeared, along with modern fi sh. A huge mass extinction event wiped out the dinosaurs at the end of the Cretaceous Period, probably due to the impact of a large meteorite.
What major climatic and biologic events happened during the Pleistocene?
Much of the northern hemi sphere was in the grip of a glaciation (ice age), and there were numerous extinctions of large animals toward the end of the glaciation.
Triassic and Jurassic Life Evolution
New species filled niches vacated by extinction, Corals became dominant reef builders, Gymnosperms (cycads, conifers) proliferated, Reptiles diversified. By end of the Triassic the first true at dinosaurs appeared, Dinosaurs differ from other reptiles in significant ways (Legs are positioned beneath their bodies, bear evidence of warm bloodedness). By the end Jurassic giant sauropods were abundant. The 1st feathered birds (archaeopteryx) and the 1st ancestors of mammals appeared during the Triassic.
Chemical fluxes between living and nonliving.Involve storage and transfer between reservoirs
Nonliving reservoirs: Atmosphere Lithosphere Hydrosphere Living reservoirs: All living organisms: Microbes Plants Animals
Describe the plate- tectonic conditions that led to the formation of the Sierran arc and the Sevier thrust belt. What happened during the Laramide orogeny?
North America had a convergent- plate boundary to the west that induced collisions with microcontinents and caused subduction of oceanic crust, which partially melted to form the Sierran volcanic arc. Compression induced the folds and thrust faults just interior to the arc itself. Faulting associated with the Laramide orogeny uplifted deep basement rock to produce the Rocky Mountains, whereas earlier orogenies produced only the more superficial faults of the fold- thrust belts behind the arc. Changes from the Sevier- style orogeny may have been a result of a shallowing dip of the subducting slab.
What continents formed as a result of the breakup of Pangaea
North America, South America, Africa, Eurasia, Australia, Antarctica, and the microcontinent Madagascar are examples (answers may vary).
The Archean Eon (Pre-Cambrian
Oldest undisputed bacteria fossils ~ 3.2 Ga, Rocks after 3.2 Ga contain stromatolites. Photosynthesis changed Earth's atmosphere, converts CO2 and H2O to organic matter and free oxygen. The Archean Eon began about 3.85 Ga, when the first continental crust that still remains formed. This crust assembled out of volcanic arcs and hot- spot volcanoes that were too buoyant to subduct. The atmosphere contained very little oxygen, and the first life forms— bacteria and archaea— appeared.
What supercontinent formed at the end of the Paleozoic, and what ocean formed when it broke apart?
Pangaea formed at the end of the Paleozoic. When it broke up, the Atlantic Ocean basin formed.
Cenozoic
Recent life. The most recent portion of geologic time Summary: In the Cenozoic Era, the collision of Africa and India with Asia and Europe formed the Alpine- Himalayan orogen. Convergent tectonics persisted along the margin of South America, creating the Andes, but ceased in North America when the San Andreas Fault formed. Rifting in the western United States produced the Basin and Range Province. Various kinds of mammals filled niches left vacant by the dinosaurs, and the human genus, Homo, appeared and evolved through the Pleistocene Ice Age.
fossil
any remains, impression, or trace (tracks, trails, burrows, etc.) of a living thing of a former geologic age, as a skeleton, footprint, etc.
Cretaceous life evolution
Swimming reptiles and gigantic turtles swam the seas. Angiosperms (flowering plants) appeared and spread. Dinosaurs reached their evolutionary peak. Inhabited almost all environments on earth. Social herds of grazing dinosaurs roamed the plains. Large carnivores fed upon the herbivores. Pterosaurs soared overhead, birds began to diversify. Mammals developed larger brains and specialized teeth.
How did the Alleghenian and Ancestral Rocky orogenies affect North America?
The Alleghenian orogeny provided the fi nal uplift to produce the Appalachian Mountains. This powerful collision between Laurentia and Gondwana influenced fault movement in what is now western North America. Uplifted western blocks (the Ancestral Rockies) are the first tectonic events in the region of the modern Rocky Mountains.
What caused the Himalayas and the Alps to form?
The Alps arose from Europe's collision with Africa; the Himalayas arose from India's collision with Asia.
What major tectonic provinces formed in the western United States during the Cenozoic?
The Basin and Range Province and the Snake River Plain Province are two important examples.
How did the atmosphere and tectonic conditions change during the Proterozoic Eon?
The atmosphere became oxygenated (and depleted of some carbon dioxide) as a result of photosynthesis. Plate- tectonic conditions became more similar to what is observed today, with larger oceanic plates and the development of broad, stable cratons in continental interiors.
Describe the condition of the crust, atmosphere, and oceans during the Hadean Eon.
The crust would have been largely ultramafic magma and rock (which may have been subject to remelting). The atmosphere lacked free oxygen and would have been dominated by volcanically emitted gases (water vapor, nitrogen, and carbon dioxide). For at least part of the Hadean, temperatures were likely too hot to sustain a liquid ocean.
What could have caused the K-T mass extinctions?
The extraterrestrial impact that produced the Chicxulub crater was likely a factor. (The Deccan Traps eruption is another, unmentioned in the text - but we discussed the increase in volcanism during lecture.)
Cenozoic paleogeography
The final stages of the breakup of Pangaea. Global climate has gradually cooled since the Cretaceous. The Antarctic ice cap reappeared in the early Oligocene. Continued cooling led to the formation of grasslands. The Isthmus of Panama emerged 2.5 Ma (Isolated circulation between the Atlantic and the Pacific, Permitted the Arctic Ocean to freeze).
What is the ozone hole, and how does it affect us?
The ozone hole is a region in the stratospheric ozone layer over Antarctica (a smaller hole sits atop the Arctic) where the volume of ozone has been dramatically reduced due to the reaction of ozone with anthropogenic chlorofluorocarbons. The increased ultraviolet radiation that results can lead to increased rates of skin cancer and potentially other forms of cancer.
How do paleoclimatologists study ancient climate change?
The record of sedimentary rocks can be used to decipher ancient climate change because certain rocks are characteristic products of specific environments; further, fossils provide environmental clues because many organisms have narrow environmental tolerances. Oxygen isotope ratios in ice and carbonate sediments provide a proxy for average temperatures. Ancient air bubbles may reveal atmospheric carbon dioxide levels (and thus the effectiveness of Earth's green house). Variations in growth rings and recorded human history can be used to infer climate change in the very recent past.
Cambrian and Ordovician paleogeography
The rifted continents developed passive margin, Rising seas flooded expanses of continental crust, Epicontinental seas were shallow, warm, and sunlit, Thriving marine life was preserved as fossil-rich sediments.
The K-T (Cretaceous-Tertiary) boundary event
There is abundant evidence of catastrophic change. Instantaneous global change in fossil assemblages. Sudden mass extinction of most species on earth. The dinosaurs that had ruled the planet for 150 Ma vanished. Catastrophic impact by a 10 km comet or meteorite. The Chicxulub crater lies beneath the northern Yucatan. Radiometric dating indicates the crater formed at ~ 65 Ma. Iridium in the clay is rare on Earth; common in meteorites. Iridium-enriched clay found at the K-T boundary worldwide.
How did the Cambrian explosion of life change the nature of the living world?
These first abundant animals complicated the world food web through the introduction of more abundant filter and bottom (deposit) feeders, as well as large, mobile predators and the first biogenic reefs. Carnivores likely induced selection pressure favoring numerous defensive structures (thick shells, spines) and behaviors (burrowing, active swimming).
Why can we find mineral grains that are older than the oldest rocks?
These oldest minerals grains are zircons found in sedimentary rocks. Isotopic dates for the zircons give the age of the original igneous rocks in which they formed. These original igneous rocks have been destroyed by the weathering process. The sandstones in which the zircon grains are found are younger than these isotopic dates (principle of inclusions), and no rocks have been found that are as old as these zircon grains.
What are some of the likely scenarios for the long- term future of the Earth?
Unless destroyed by impact (which is very unlikely), Earth will most likely be consumed by the red- giant stage of our Sun's evolution, approximately 5 billion years from now.
Describe how the first continental crust might have formed.
Volcanic island arcs and hot- spot volcanoes may have become too buoyant to subduct, particularly after magmatic differentiation processes.
Were there multicellular organisms before the Cambrian?
Yes, multicellular animals and other multicellular life have been found in the late Proterozoic Ediacaran faunas.
Did supercontinents form in the Proterozoic?
Yes; Rodinia formed late in the Proterozoic.
Carrying capacity
capacity is the maximum number of individuals of a given species that an area's resources can sustain indefinitely without significantly depleting or degrading those resources.
Cetaceans (whales)
evolve from land dwelling mammals - artiodactyls (antelopes) and enter the water/seas in the early Eocene Epoch. They re-occupied niches that existed after the extinction of the marine reptiles at the end of the Cretaceous.
The Georgia Coastal Plain
is a sedimentary sequence that ranges in age from Cretaceous to Holocene. It is predominately marine in origin and as a result the vast majority of fossils that are preserved are marine organisms.
Computer models are used to predict climate changes.
o By 2050, average annual T will increase by 1.5oC to 2.0oC. o By 2150, global T may be 5oC to 11oC warmer than present.
o Without sustainability, Earth and humans will be in trouble.
o Earth System disruption will reach a critical point based on: o Natural resource limitations (fuels, metals, water) o Shrinking land areas o Increasing populations Under such a scenario, a new equilibrium will need to be reached.
• Human additions of CO2 and CH4 exceed natural removals
o Fossil fuel combustion (CO2) o Rice-paddy decay (CH4) o Livestock (CH4)
Many scientists think that global warming could lead to:
o Interruption of the oceanic heat conveyor system
Thousands of observations worldwide have documented effects of recent global warming: Examples:
o Large ice shelves, like the Larsen B along the Antarctic Peninsula, are breaking up. o The summer melt line indicates that melting of the Greenland ice sheet is accelerating. o Valley glaciers worldwide are retreating. o Arctic Ocean sea-ice is reduced.
• Major extinctions
o Late Ordovician o Mid-Late Devonian o End Permian o Late Triassic. o End Cretaceous
Our future on Earth requires sustainable growth.
o Prosperity based on balancing societal and human needs o Our limitations are Earth's finite resources.
The predicted effects of global warming:
o Stronger storms due to a more vigorous hydrologic cycle: o Higher sea-surface temperatures o Greater evaporation o Greater differential pressures o 2005 set a number of storm records o A rise in sea level o Sea level is now rising 1-2 mm/year. o Warming will accelerate this trend by: Thermal expansion of seawater Melting polar ice
Most scientists accept global warming as fact
o Surface air temperatures have warmed by ~ 1oC since 1880. o This equates to an approximate 500 mile change in local temp. (Washington D.C. to Charleston SC) o Global average temperature is higher today than in the last 2,000 years
o Polar ice meltwater is freshwater.
o Would dilute surface ocean water near the poles. o This freshwater won't sink and move southward. o Thermohaline circulation would stop preventing warm water from flowing northward.
Mass Extinction events
the stratigraphic record contains evidence of dramatic decreases in biodiversity. • Catastrophic changes • Large numbers of species disappear forever • Millions of years needed for biodiversity to recover
Pollution
—materials that harm life forms and resources Modern human society generates contaminants. Contaminating materials are numerous and diverse. • They are produced so fast that the natural environmental systems can't absorb or modify/neutralize them.
The carbon cycle:
• A biogeochemical cycle that regulates climate - Volcanic CO2 adds carbon to the atmosphere. - Atmospheric CO2 is removed in several ways: • It dissolves in water as carbonic acid and bicarbonate. • Photosynthesis removes CO2. • Weathering
Pollution causes acidification
• Acid runoff—sulfide minerals dissolve and release acid. o Coal mining o Metal mining • Acid precipitation—sulfide-rich aerosols acidify rain. o Coal-fired power plants o Ore smelters
Recent global warming—human greenhouse gas additions alter climate.
• CO2 in the atmosphere has steadily climbed since the industrial revolution began. o Ice core data show atmospheric CO2 in 1750 was ~ 280 ppm. o In 1958, CO2 was ~315 ppm; in 2010, CO2 was ~390 ppm.
Pollution causes depletion of stratospheric ozone (O3).
• Chlorofluorocarbons (CFCs) catalyze destruction of ozone. • Stratospheric ozone protects Earth from UV radiation. • Ozone depletion is harmful to many life forms. • Note: Ozone depletion is unrelated to CO2 buildup.
Long-term climate change causes
• Complex interactions across the Earth System • Plate tectonics modifies the position of continents. • Uplift of land surfaces influences atmospheric circulation. • Formation of coal and oil removes carbon from atmosphere. • Evolution of life affected atmospheric composition.
Ecosystem modifications—destroy habitats
• Deforestation • Overgrazing • Agriculture • Urbanization
Short-term climate change causes
• Fluctuations in solar radiation and cosmic rays • Changes in Earth's orbit and tilt • Changes in volcanic emissions • Changes in ocean currents • Changes in surface albedo • Abrupt changes in concentrations of greenhouse gases
Ecosystem modification—balances are destabilized
• Human-caused changes occur faster than indigenous organisms can adapt. • Rainforest decline is largely the result of human activity.
Landscape modifications
• Human-induced erosion may exceed natural processes. Example=increased erosion in the SE US due to improper agricultural pratices
The Proterozoic Eon
• Over the last 500 Ma of the Proterozoic... • A gigantic leap in biological complexity. • Simple organisms gave way to complex ones. • Ediacaran fauna - Unusual soft-bodied fossils In the Proterozoic Eon, which began at 2.5 Ga, Archean cratons sutured together to form large cratons. Photosynthesis added oxygen to the atmosphere. By the end of the Proterozoic, soft- bodied marine invertebrates populated the planet, and continental crust had accumulated to form a supercontinent
Paleoclimate
• Paleoclimates—past climates are interpreted by datable Earth materials that are climate-sensitive. - Stratigraphic records—sequences of rock strata • Depositional environments are often climate-sensitive. - Glacial tills—cold and continental - Coral reef— tropical marine
Pollution causes water contamination.
• Pollutants frequently enter surface and groundwater. o Sanitary wastes o Fuel and oil o Solvents o Fertilizers o Pesticides
