Text: Historical Geology Evolution of Earth and Life Through Time 4th edition by Wicander and Monroe

The Dynamic and Evolving Earth Chapter 1 The Dynamic and Evolving Earth

The Movie of Earth’s History What kind of movie would we see if it were possible to travel back in time and film Earth’s History from its beginning 4.6 billion years ago? It would certainly be a story of epic proportions with great special effect and a cast of trillions twists and turns in its plot with an unknown ending Although we cannot travel back in time, the Earth’s History is still preserved in the geologic record

Subplot: Landscape History In this movie we would see a planet undergoing remarkable change as continents moved about ocean basins opened mountain ranges grew along continental margins and where continents collided The oceans and atmosphere would form and grow change circulation patterns cause massive ice sheets to form and grow and then melt away Extensive swamps or vast interior deserts would sweep across the landscape

Subplot: Life’s History We would also witness the first living cells evolving from a primordial organic soup between 4.6 and 3.6 billion years ago Cell nuclei would evolve, then multicelled soft-bodied animals followed by animals with skeletons and then backbones The barren landscape would come to life as plants and animals moved from their watery home insects, amphibians, reptiles, birds and mammals would eventually evolve

Earth is a Dynamic and Evolving Planet Changes in its surface Changes in life Images from left to right: Changes in its surface Artist’s rendition of how Earth is thought to have appeared about 4.6 billion years ago. Paleogeography of the world for the Late Cambrian Period. Apollo 17 view of Earth. Africa, Arabian Peninsula, Madagascar, Antarctica, South Atlantic Ocean , Indian Ocean. Changes in life Possible precursor of life: bacterium-like proteinoid. Reconstruction of Middle Devonian reef from the Great Lakes area Shown are corals, ammonoids, trilobites and brachiopods. Cretaceous Pteranodon.

At the End of the Movie The movie’s final image is of Earth, a shimmering blue-green oasis in the black void of space and a voice says, “To be continued.”

The Movie’s Theme Every good movie has a theme, and “The History of Earth” is no exception Three interrelated themes run throughout it The first is that Earth’s outermost part is composed of a series of moving plates Plate tectonics whose interactions have affected its physical and biological history The second is that Earth’s biota has evolved or changed throughout its history organic evolution

Earth is a System of Interconnected Subsystems Atmosphere (air and gases) Hydrosphere (water and oceans) Biosphere (plants and animals) Lithosphere (Earth’s rocky surface) Interior (mantle and core)

Interactions in Earth’s Subsystems Atmosphere Biosphere Gases from respiration Transport of seeds and spores

Interactions in Earth’s Subsystems Wind erosion, transport of water vapor for precipitation Mountains divert air movements Atmosphere Lithosphere

Interactions in Earth’s Subsystems Source of sediment and dissolved material Water and glacial erosion, solution of minerals Hydrosphere Lithosphere

This class is about historical geology What is Geology? From the Greek geo (Earth) logos (reason) Geology is the study of Earth Physical geology studies Earth materials, such as minerals and rocks as well as the processes operating within and on Earth’s surface

Historical Geology In historical geology we study changes in our dynamic planet how and why past events happened implication for today’s global ecosystems Principles of historical geology not only aid in interpreting Earth’s history but also have practical applications William Smith, an English surveyor/engineer used study of rock sequences to help predict the difficulty of excavation in constructing canals

Scientific Method The scientific method an orderly and logical approach Gather and analyze facts or data A hypothesis is a tentative explanation to explain observed phenomena Scientists make predictions using hypotheses then they test the predictions After repeated tests, if one hypothesis continues to explain the phenomena, scientists propose it as a theory

Formulation of Theories Theory colloquial usage - speculation or conjecture scientific usage coherent explanation for one or several related natural phenomena supported by a large body of objective evidence

Origin of the Universe The Big Bang occurred 15 billion years ago and is a model for the beginning of the universe

Evidence for the Big Bang Universe is expanding How do we determine the age? measure the rate of expansion backtrack to a time when the galaxies were all together at a single point Pervasive background radiation of 2.7º above absolute zero is the afterglow of the Big Bang

Big Bang Model Initial state: During 1st second: No time, matter or space existed There is no “before the Big Bang” Universe consisted of pure energy During 1st second: Very dense matter came into existence The four basic forces separated gravity, electromagnetic force, 2 nuclear forces Enormous expansion occurred

Big Bang Model (cont.) 300,000 years later: atoms of hydrogen and helium formed light (photons) burst forth for the first time During the next 200 million years: Continued expansion and cooling Stars and galaxies began to form Elements heavier than hydrogen and helium began to form within stars by nuclear fusion

Features of Our Solar System In a spiral arm of the Milky Way Galaxy Sun 9 planets 101 known moons (satellites) a tremendous number of asteroids most orbit the Sun between the orbits of Mars and Jupiter millions of comets and meteorites interplanetary dust and gases

Relative Sizes of the Sun and Planets

Solar System Configuration

Origin of Our Solar System Solar nebula theory cloud of gases and dust formed a rotating disk condensed and collapsed due to gravity forming solar nebula with an embryonic Sun surrounded by a rotating cloud

Embryonic Sun and Rotating Cloud Planetesimals have formed in the inner solar system, and large eddies of gas and dust remain far from the protosun

The Planets Terrestrial Planets Mercury Venus Earth Mars small, composed of rock, with metal cores Jovian Planets Jupiter Saturn Uranus Neptune large, composed of hydrogen, helium, ammonia, methane, relatively small rocky cores

Earth’s Very Early History Started out cool about 4.6 billion years ago probably with uniform composition/density Mostly: silicate compounds iron and magnesium oxides Temperature increased. Heat sources: meteorite impacts gravitational compression radioactive decay Heated up enough to melt iron and nickel

Earth’s Differentiation Differentiation = segregated into layers of differing composition and density Early Earth was probably uniform Molten iron and nickel sank to form the core Lighter silicates flowed up to form mantle and crust

Forming the Earth-Moon System Impact by Mars-sized or larger planetesimal with young Earth 4.6 to 4.4 billion years ago ejected large quantity of hot material, and formed the Moon

Forming the Earth-Moon System Most of the lunar material came from the mantle of the colliding planetesimal The material cooled and crystallized into lunar layers

Forming the Earth-Moon System Most of the lunar material came from the mantle of the colliding planetesimal The material cooled and crystallized into lunar layers

Moon Light-colored areas are lunar highlands Provide striking evidence Heavily cratered Provide striking evidence of massive meteorite bombardment

Earth—Dynamic Planet Earth was also subjected to the same meteorite barrage that pock-marked the Moon Why isn’t Earth’s surface also densely cratered? Because Earth is a dynamic and evolving planet Craters have long since been worn away

Earth’s Interior Layers Crust - 5-90 km thick continental and oceanic Mantle composed largely of peridotite dark, dense igneous rock rich in iron and magnesium Core iron and a small amount of nickel

Earth’s Interior Layers Lithosphere solid upper mantle and crust Crust - 5-90 km thick continental and oceanic Mantle composed largely of peridotite dark, dense igneous rock rich in iron and magnesium Asthenosphere part of upper mantle behaves plastically and slowly flows Core iron and a small amount of nickel

Earth’s Interior Layers Lithosphere solid upper mantle and crust broken into plates that move over the asthenosphere Asthenosphere part of upper mantle behaves plastically and slowly flows

Earth’s Crust outermost layer continental (20-90 km thick) density 2.7 g/cm3 contains Si, Al oceanic (5-10 km thick) density 3.0 g/cm3 composed of basalt

Plate Tectonic Theory Lithosphere is broken into individual pieces called plates Plates move over the asthenosphere as a result of underlying convection cells

Modern Plate Map

Plate Tectonic Theory At plate boundaries Movement at plate boundaries Volcanic activity occurs Earthquakes occur Movement at plate boundaries plates diverge plates converge plates slide sideways past each other

Plate Tectonic Theory Types of plate boundaries Divergent plate boundary Mid-oceanic ridge Continental-continental convergent plate boundary Continental-oceanic convergent plate boundary Oceanic-oceanic convergent plate boundary Trench Transform plate boundary

Plate Tectonic Theory Influence on geological sciences: Revolutionary concept major milestone comparable to Darwin’s theory of evolution in biology Provides a framework for interpreting many aspects of Earth on a global scale relating many seemingly unrelated phenomena interpreting Earth history

Plate Tectonics and Earth Systems Plate tectonics is driven by convection in the mantle and in turn drives mountain building and associated igneous and metamorphic activity Solid Earth Arrangement of continents affects solar heating and cooling, and thus winds and weather systems Rapid plate spreading and hot-spot activity may release volcanic carbon dioxide and affect global climate Atmosphere

Plate Tectonics and Earth Systems Continental arrangement affects ocean currents Rate of spreading affects volume of mid-oceanic ridges and hence sea level Placement of continents may contribute to the onset of ice ages Hydrosphere Movement of continents creates corridors or barriers to migration, the creation of ecological niches, and transport of habitats into more or less favorable climates Biosphere

Theory of Organic Evolution Provides a framework for understanding the history of life Darwin’s On the Origin of Species by Means of Natural Selection, published in 1859, revolutionized biology

Central Thesis of Evolution All present-day organisms are related and descended from organisms that lived during the past Natural selection is the mechanism that accounts for evolution Natural selection results in the survival to reproductive age of those organisms best adapted to their environment

History of Life The fossil record provides perhaps the most compelling evidence in favor of evolution Fossils are the remains or traces of once-living organisms Fossils demonstrate that Earth has a history of life

Geologic Time From the human perspective time units are in seconds, hours, days, years Ancient human history hundreds or even thousands of years Geologic history millions, hundreds of millions, billions of years

Geologic Time Scale Resulted from the work of many 19th century geologists who pieced together information from numerous rock exposures, constructed a sequential chronology based on changes in Earth’s biota through time The time scale was subsequently dated in years using radiometric dating techniques

Geologic Time Scale

Uniformitarianism Uniformitarianism is a cornerstone of geology is based on the premise that present-day processes have operated throughout geologic time The physical and chemical laws of nature have remained the same through time To interpret geologic events from evidence preserved in rocks we must first understand present-day processes and their results Rates and intensities of geologic processes may have changed with time

How Does the Study of Historical Geology Benefit Us? Survival of the human species depends on understanding how Earth’s various subsystems work and interact Study what has happened in the past, on a global scale, to try and determine how our actions might affect the balance of subsystems in the future

We “Live” Geology Our standard of living depends directly on our consumption of natural resources resources that formed millions and billions of years ago How we consume natural resources and interact with the environment determines our ability to pass on this standard of living to the next generation

Summary Earth is a system Geology is the study of Earth of interconnected subsystems Geology is the study of Earth Historical geology is the study of the origin and evolution of Earth Scientific method is an orderly, logical approach to explain phenomena, using data, formulating and testing hypotheses and theories Universe began with a big bang 15 billion years ago

Summary Solar system formed 4.6 billion years ago by condensation and gravitational collapse of a rotating interstellar cloud Earth formed 4.6 billion years ago as a swirling eddy in the solar system nebula Moon may have formed when a planetesimal collided with Earth 4.6 to 4.4 billion years ago Earth probably started solid then differentiated into layers as it heated and melted

Summary Earth’s layers mostly solidified into the core, mantle and crust, with the upper mantle and crust making up the soft asthenosphere and the solid lithosphere Lithosphere is broken into plates that diverge, converge and slide sideways past each other Plate tectonics is a unifying theory that helps explain features and events including volcanic eruptions, earthquakes and mountain forming

Summary Central thesis of organic evolution is An appreciation that all living organisms evolved from organisms that existed in the past An appreciation of the immensity of geologic time is central to understanding Earth’s evolution Uniformitarianism holds that the laws of nature have been constant through time Geology is part of our lives and our standard of living depends on our use of natural resources that formed over billions of years