Earth and Life Science Midterms PDF

**EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG +-----------------------------------------------------------------------+ | Topic Outline: | | | | Theories on the Origin of...

**EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG +-----------------------------------------------------------------------+ | Topic Outline: | | | | Theories on the Origin of The Universe | | | | Earth's Subsystems | | | | Earth's Internal Structure | | | | Rocks and Minerals | | | | Weathering, Erosion, Deposition | | | | Magma and Volcanism | | | | Plate Boundaries | | | | Geological Time | +-----------------------------------------------------------------------+ **THEORIES ON THE ORIGIN OF THE UNIVERSE** **Cosmology** o Branch of astronomy involving the science of the universe's origin. **MODERN THEORIES ON** **THE ORIGIN OF THE UNIVERSE** 1\. Big Bang Theory o Current accepted model on the formation of the universe. o Universe as expanding. o Originated from an infinitely tiny, infinitely dense point. o Only pure energy compressed in a single point called *singularity*. o Caused the inflation of the universe. o 4 fundamental forces formed: ▪ Gravity -- attraction between bodies ▪ Electromagnetic Force -- bonds atom into molecules ▪ Strong Nuclear Force -- binds protons and neutrons together in nucleus ▪ Weak Nuclear Force -- break down atom's nucleus o Attributed to Belgian Roman Catholic Priest *Georges Lemaitre* o Supported by *Edwin Hubble* (observation of galactic redshifts), Arno Penzias and Robert Wilson (cosmic microwave background radiation) 2\. Oscillating Theory o Albert Einstein's favored model. o Followed the general theory of relativity equations of the universe with positive curvature. o Resulted in the expansion of universe for a time. o Contraction due to the pull of gravity. o In the Friedmann models, the average mass density is constant over all space but may change with time as the universe expands. 3\. Steady State Theory o Proposed by astronomers Fred Hoyle, Thomas Gold, and Herman Bondi. o Expanded but did not change its density. o Matter was inserted into the universe as its expanded to maintain a constant density. 4\. Inflationary Universe o American physicist Alan Guth proposed a model base on big bang theory. o Early universe expanded *exponentially fast* for a fraction of a second after the Big Band. (horizon and flatness) o Known as Inflationary model 5. Multiverse MIDTERMS \| 1 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG o Inflationary Universe from Inflation Theory o One of many "bubbles" that grew as part of universe. o Hugh Everett III and Bryce DeWitt initially popularized "many worlds" **THEORIES ON THE ORIGIN OF THE SOLAR SYSTEM** 1\. Encounter Hypothesis o One of the earliest theories for the formation of the planets. o Rogue star passes close to the sun. o Materials (hot gases) is tidally stripped from the sun and the rogue star. o Able to explain why *all planets revolve in the same direction* and why the *inner planets are denser* *than the outer planets.* 2\. Nebular Hypothesis o Self-gravity contracts a gas cloud. o Large cloud of gas that contracts due to self gravity. o Conservation of angular momentum requires that a rotating disk form with a large concentration at the center (the proto-sun). Within the disk, planets form. o This theory incorporates more basic physics, there are several unsolved problems. o For example, a majority of the angular momentum in the Solar System is held by the outer planets. o For comparison, 99% of the Solar System's mass is the sun, but 99% of its angular momentum is in the planets. o Another flaw is the mechanism to explain why the disk would turn into individual planets. 3\. Protoplanet Hypothesis o The current working model for the formation of the Solar System. o Built on the main concepts of the nebular hypothesis. o Solar System started from a nebula that was disrupted which led to the formation of protoplanets. o "remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious. And however difficult life may seem, there is always something you can do and succeed at. It matters that you don't just give up." -- Stephen **CHARACTERISTICS OF THE EARTH MAKES IT HABITABLE:** 1\. Right distance from the sun. 2\. Magnetic field that protects it from harmful solar radiation. 3. Insulating atmosphere that keep the planet warm. 4. Right chemical ingredients for life including water and carbon. 5\. Processes that shape the Earth and its environment and constantly cycle elements through the planet. **FACTORS THAT MAKE A PLANET HABITABLE:** 1\. Temperature o Life seems to be limited to a temperature range of -15 OC to 115 OC. In this range, liquid water can still exist under certain condition. 2\. Atmosphere o Earth and Venus are the right size to hold a sufficient sized atmosphere. It keeps the surface warm and protects it from radiation and small to medium sized meteorites. 3\. Energy o With a steady input of either light or chemical energy, cells can run the chemical reactions necessary for life. 4\. Nutrients o All solid planets and moons have the same general chemical makeup, so nutrients are present. Those with a water cycle or volcanic MIDTERMS \| 2 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG activity can transport and replenish the chemicals required by living organisms. **FACTS ABOUT EARTH** Earth is about 4.5 billion years old, approximately one-third of the age of the universe. According to the Nebula Theory, it was formed at the same time as the other members of the solar system by accretion from the solar nebula. During its billion years of evolution, Earth has gone through a series of major biological and geological changes. Examples: o Volcanic eruptions o Collisions of plate boundaries o Creation and destruction of mountain ranges and seabeds The earth also suffered from constant bombardment from meteorites and other cosmic bodies. Effects: o Tilting of Earth o Formation of its Satellite o The Moon When seen from outer space, Earth is a small blue planet bathing in a film of white clouds and liquid water. Out planet is composed of different spheres or layers. "Earth is divided yet connected." **EARTH'S SYSTEMS AND PROCESSES** The earth system is all of the matter, energy, and processes within Earth's boundary. Earth is a complex system made of living and nonliving things, matter, and energy continuously cycle through the smaller systems. **ATMOSPHERE:** Earth's invisible gases A mixture of mostly invisible gases that surround Earth.  Layers of the Atmosphere o Exosphere -- satellites orbit o Thermosphere -- temperatures can vary greatly. o Mesosphere -- most meteoroids burn up here. o Stratosphere -- ozone is formed in this layer. o Troposphere -- where we live and weather happens. **HYDROSPHERE:** Earth's liquid water The part of Earth that is liquid water. Example: o Oveans o Lakes o Rivers o Marshes o Groundwater o Rain o The water droplets in clouds Earth is the only planet in the solar system that has water in all of its three phases. o Ice o Water o Steam 1\. Evaporation o Happens when water molecules at the surface of water bodies become excited and rise into the air. 2. Condensation o Vapours become tiny droplets of water and ice, eventually coming together to form clouds. 3\. Precipitation o When enough droplets merge, it falls out of the clouds and on the ground below. 4\. Transpiration o Process of water vapor being released from plants and soil. 5\. Infiltration o Water that has fallen as rain is absorbed into the ground. 6\. Surface runoff o Flowing down the sides of mountains and hills; eventually forming rivers. **CRYOSPHERE:** Made up of all of the frozen water on Earth. Example: MIDTERMS \| 3 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG o Snow o Ice o Sea ice o Glaciers o Ice shelves o Icebergs o Permafrost **GEOSPHERE:** Earth's solid, rocky part The mostly solid, rocky part of Earth. It extends from the center of Earth to the surface of Earth. Understanding the Earth's structure: o Where we live -- compose f different continents. o Crust -- outermost layer of the geosphere. o Inner core -- innermost layer of the geosphere. o Upper mantle -- adjoins the crust to form the lithosphere. o Outer core -- liquid layer, composed of iron and nickel. o Lower mantle -- much less ductile than the upper mantle. **BIOSPHERE:** Earth's living things Made up of living things and the areas of Earth where they are found. Life on Earth exists within this zone where interactions among the four subsystems occur and create habitable environment. **HOW DO EARTH'S SPHERES INTERACT?** All of the five spheres of Earth interact as matter and energy change and cycle through the system. Earth's spheres interact as matter moves between them. In some processes, matter moves through several spheres. Earth's spheres also interact as energy moves from one sphere to another, and back and forth between spheres. The interaction among Earth's subsystems is vital in sustaining life on the planet. **EARTH'S GEOSPHERE** Refers to the solid part of the Earth, including the rocks, minerals, landforms, and the processes that shape them. **LAYERS OF THE EARTH** 1\. Crust o The outermost layer of the Earth. o It is the thinnest layer, ranging from about 5 to 70 kilometers in thickness. 2\. Mantle o The layer beneath the Earth's crust. o It is the thickest layer, extending from the base of the crust to a depth of approximately 2,900 kilometers. 3\. Core o The innermost layer of the Earth, situated beneath the mantle. o It is divided into two distinct regions: ▪ Outer core ▪ Inner core **WHAT REALLY IS INSIDE THE EARTH?** Through the study of seismic waves, scientists inferred that our planet is made up of different layers. As seismic waves travel through the Earth, they are refracted and their speed gave vital information on the composition of the different layers of the Earth. Mechanically o Lithosphere ▪ Outer solid part of the planet including Earth's crust as well as the underlying cool, dense, and rigid upper part of the mantle. o Asthenosphere ▪ A highly viscous, hotter, and ductile region of the upper mantle that is involved in plate tectonic movement and isostatic adjustments. o Mesospheric mantle o Outer core o Inner core Chemically o Crust ▪ Outermost layer of the Earth; thinnest layer, makes up only about 1% of the earth. ▪ Continental Crust ❖ Under the continents, the crust thickens up to 35km and reaches depths up to 60km under some mountain ranges. ▪ Oceanic crust ❖ Under the oceans, the crust is only about 5-10km thick. ▪ Most common elements in the crust: ❖ Oxygen -- 46.6% ❖ Silicon -- 27.7% MIDTERMS \| 4 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG ❖ Aluminum -- 8.1% ❖ Iron -- 5% ❖ Calcium -- 3.6% ❖ Sodium -- 2.8% ❖ Potassium -- 2.6% ❖ Magnesium -- 2.1% ▪ The average composition of the crust has been identified from scientific analyses of rocks and minerals taken from the surface or underground. ▪ The elements account for about 98.5% of the total weight of the crust. ▪ Most earthquakes occur in the crust. o Mantle ▪ MOHOROVICIC DISCONTINUITY ▪ Also called as MOHO ▪ Separates the crust from the mantle. ▪ Discovered by a Croatian seismologist, Andrija Mohorovicic in 1909. ▪ Largest layer of the earth; composed of iron, aluminum, calcium, magnesium, silicon, and oxygen about 80% of the planet' mass is concentrated on mantle. ▪ Upper mantle ❖ Seen as a highly viscous layer which lies between the crust and the lower mantle. ▪ Lower mantle ❖ Under tremendous pressure and therefore has a lower viscosity than the upper mantle. o Core ▪ Earth's source of internal heat because it contains radioactive materials which release heat as they break down into more stable substance. ▪ Outer core ❖ Made up of iron, some nickel, and about 10% sulfur and oxygen. ❖ Temperature is about 5000C so it remains in its liquid state. ▪ Inner core ❖ Inner most layer of the Earth ❖ A solid hot ball that is submerged in the liquid outer core. **ROCKS AND MINERALS** The study of rocks is important because their mineral and chemical compositions and fossil contents can be used to reconstruct Earth's history and understand how life evolved. **MINERALS** Building blocks of rocks Is homogeneous, naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. Physical property o Observed with senses. o Determined without destroying matter. Chemical Property o Indicates how a substance reacts with something else. o Natter will be change into a new substance after reaction. o The structure of a mineral (the way atoms are stacked) depends on its chemical composition as well as the conditions of temperature and pressure during crystallization. **THREE BASIC PROCESSES ARE RESPONSIBLE FOR THE FORMATION OF MINERALS:** 1\. Minerals form in saturated fluids when dissolved ions have reached their solubility threshold. 2\. Minerals form by solidification (liquid-solid transition) or deposition. 3\. Minerals form by biological processes. **PHYSICAL PROPERTIES OF MINERALS** 1\. Crystal habit o Refers to the overall shape or growth pattern of the mineral. It can be described as: ▪ Equant -- 3D of mineral have both the same length. ▪ Elongate -- forms prismatic or prism-like crystals. ▪ Platy -- flattened and thin crystal. o Overall shape or growth pattern. 2. Luster o Describes the appearance of mineral when light is refracted from its surface. It can describe as opaque, transparent, dull, or shiny. ▪ Metallic Luster -- opaque and very reflective like gold and silver. ▪ Nonmetallic Luster -- dull, silky, greasy, and pearly like silicates. o Appearance of mineral when light is reflected. 3\. Cleavage and Fracture o Cleavage refers to the tendency of minerals to break along very smooth, flat, shiny surfaces. ▪ Mica -- one direction; sheet MIDTERMS \| 5 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG ▪ Galena -- three; cubic shape o A mineral fracture may break along random, irregular surfaces. o Example: ▪ Sulfur ▪ Bauxite ▪ Hematite ▪ Quartz o Tendency of mineral to break. 4\. Hardness o A measure of mineral's resistance from scratching. o Harder minerals will scratch softer minerals. o Friedrich Mohs in 1812 ranked minerals according to hardness. He selected 10 minerals of distinctly different hardness that ranged from very soft mineral (talc) to a very hard mineral (diamond). o Mineral's resistance to scratching. 5. Color o Is one of the most obvious properties of a minerals but not reliable alone. o Color may vary due to: ▪ Natural coloring agents -- impurities ▪ Weathering; exposure to the environment o Most obvious property 6\. Streak o Refers to the color of the mineral in its powdered form. o Determined by using a streak plate: ▪ Quartz -- white/ colorless ▪ Hematite -- reddish brown o Color of mineral in its powdered form. **ADDITIONAL PROPERTIES** Magnetism o Some mineral are attracted to a hand magnet. Striations o Presence of very thin, parallel grooves Specific gravity o Weight of mineral divided by weight of an equal volume of water. Taste, Odor, Feel o Some minerals have distinctive taste, odor, or feel. **CHEMICAL COMPOSITION OF MINERALS** Silicate minerals o Silicon and oxygen groupings; SiO2 o Combined with one or more metals. o Largest group of minerals. Non-silicate minerals o Do not contain SiO2. o Subdivided into several other classes. o Extremely rare o Few are relatively common. **CHEMICAL PROPERTIES OF MINERALS** 1\. Native elements o Are minerals that consist of only one element and thus the element occurs in the native state. o Example: ▪ Gold (Au) ▪ Sulfur (S) ▪ Silver (Ag) o Native elements are minerals composed of only one element. 2\. Silicates o Are minerals whose chemical elements include silicon and oxygen, SiO2. o Silicates make up about 95 percent of the Earth's crust. o Example: ▪ Feldspa 3\. Oxides o Are minerals that contain oxygen bonded with one or more metals. o Example: ▪ Hematite (Fe203) ▪ Magnetite (Fe304) 4\. Sulfides o Are minerals whose chemical elements include sulfur bonded to a metal ion. o Example: ▪ Pyrite (FeS2) -- "fool's gold". 5\. Sulfates MIDTERMS \| 6 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG o Made of compounds of sulfur combined with metals and oxygen. o Example: ▪ Gypsum 6\. Halides o Form from halogen elements like chlorine, bromine, fluorine, and iodine combined with metallic elements. o Example: ▪ Halite (NaCl) -- table salt 7\. Carbonates o Are minerals whose chemical elements include carbon and oxygen as a major part of their chemical composition. o Example: ▪ Dolomite 8\. Phosphates o Formed when other minerals are broken down by weathering. o Example: ▪ Apatite 9\. Mineraloid o Term used for those substances that do not fit neatly into one of the eight classes. o Example: ▪ Amber **ROCKS** Aggregate of minerals **ROCKS IN RELATION TO MINERALS** Rocks o Many kinds of rocks are composed of minerals. Monomineralic o Rocks that are composed of only one mineral. Polymineralic o Rocks that are composed of two or more minerals. Quantity o There are almost 4,700 different minerals. **CLASSIFICATION OF ROCKS** 1\. Igneous Rocks o Form by solidification of cooling magma (molten rock) o Intrusive rocks ▪ Plutonic rock ▪ Formed from solidified magma underneath the earth. o Extrusive rocks ▪ Volcanic rock ▪ Formed on the surface of the earth. ▪ They are cooled lava. 2\. Sedimentary Rocks o Form by accumulation and subsequent lithification of sediments. o Clastic ▪ Made up of sediments form preexisting rocks. o Non-clastic ▪ Biological/ organic sedimentary rock ▪ Chemical sedimentary rock 3\. Metamorphic Rocks o Form by transformation of the chemical composition and/ or texture of a preexisting rock in a solid state. o Metamorphism ▪ Process by which rising temperature and pressure or changing chemical conditions, transform rocks and minerals. o Foliated ▪ Formed through pressure due to compression of rocks that create layer produced by Regional Metamorphism. o Non-foliated ▪ It has no foliation, bands, or layers. ▪ Not exposed to the intense pressure that is found deeper within Earth. **ROCK CYCLE** A sequence of events in which rocks are formed, destroyed, altered, and reformed by geological processes. **EXOGENIC PROCESSES** Weathering o Describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. o Effects of weathering: ▪ Loss of atoms and molecules from weathered surfaces. ▪ Addition of specific atoms to the weathered surface. ▪ Breakdown of one mass into two or more masses. **CHEMICAL WEATHERING** Breaking rocks through chemical change. Formation of new compounds or new substances caused by chemical reactions. MIDTERMS \| 7 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG There are different process that result in chemical weathering including: o Hydrolysis ▪ The breakdown of rock by oxygen and water. ▪ Often giving iron-rich rocks a rusty colored weathered surface. o Hydrolysis ▪ The breakdown of rock by acidic water to produce clay and soluble salts. o Carbonation ▪ Carbon dioxide in the air dissolves in rainwater and becomes weakly acidic. ▪ This weak "carbonic acid" can dissolve limestone as it seeps into cracks and cavities. **PHYSICAL WEATHERING** Breakdown of rocks into pieces without any change in its composition.  In this process, the size and shape of rocks changes and this occurs because of the following factors: o Pressure o Warm temperature o Water o Ice There are different process that result in physical weathering including: o Abrasion ▪ Occurs when rocks surface is frequently exposed to water, wind, and gravity. o Freeze-thaw ▪ Occurs when water continually seeps into cracks, freezes, and expands eventually breaking the rock apart. o Exfoliation ▪ Stripping of the outer layers if rocks due to the intense heating. **BIOLOGICAL WEATHERING** Occurs when rocks are weakened by different biological agents like plants and animals. Physical means Chemical compounds **WEATHERING VS EROSION** Weathering o Describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Erosion o Separation and removal of weathered rocks due to different agents like water, wind, and glacier that causes transportation of the material. **MASS WASTING** Refers to the downslope movement of rock and soil because of gravity. Geological process in which sediments, soil, and rocks are added to a landform or landmass. Is a geological process that was formed, originated, and located below the surface of the earth. MIDTERMS \| 8 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG It involves geologic activities such as tectonic movements, metamorphism, seismic activities and magmatism. **WHAT IS A VOLCANO?** A volcano is a vent or 'chimney' that connects molten rock (magma) from within the Earth's crust to the Earth's surface. **WHY DO VOLCANOES ERUPT AND** **HOW IS MAGMA FORMED?** High temperature of the Earth's interior o Melting of lower crust = molten rock = magma The density of the magma is less than the crustal rock, therefore it rises to the surface. **TWO TYPES OF VOLCANIC ERUPTION** 1\. Explosive o Eruptions can be catastrophic. 2\. Effusive o Characterized by outpourings of lava on to the ground. **WHAT HAPPENS AFTER MAGMA IS FORMED?** Cuatro (2016) o Described that magma escaped in two forms: ▪ Intrusion -- magma that moves up into a volcano without erupting. Like a ballon, this causes the volcano to grow on the inside. ▪ Extrusion -- an eruption of magmatic materials that causes land formation on the surface of the Earth. Magma extrusion causes the formation of volcanoes. Plutonism o Refers to all sorts of igneous geological activities taking place below the Earth's surface. o The solidification and crystallization of magma takes place mainly inside the Earth's interior. Volcanism o Used to describe all geological phenomena that occurs on the natural terrestrial surface, such as the creation of volcanoes and hot springs. (Grotzinger et.al,2008) **PLATE BOUNDARIES** Are the lines at the edges of the different pieces of the lithosphere. **DIVERGENT PLATE BOUNDARIES** Formed when two tectonic plates move away from each other. Magma or molten rock escapes or rises from the Earth' Mantle to the surface or into the space between the spreading tectonic plates. Example: o Great rift valley o Mid-atlantic ridge **CONVERGENT PLATE BOUNDARIES** Happen when two plates are colliding or moving toward each other. Also called destructive boundary. Types of convergent boundary o Oceanic-continental plate boundary ▪ The denser oceanic plate slides under the continental plate. o Oceanic-oceanic plate boundary ▪ It gives rise to the formation of volcanic island arcs, trenches, and generates shallow, intermediate or deep earthquakes. o Continental-continental plate boundary ▪ There is no subduction, no trench, and no volcanoes formed. ▪ Both plates collide and buckle up causing mountain ranges. **TRANSFORM PLATE BOUNDARIES** Occurs when two plates slides past each other in a relative horizontal manner. Example: o San andreas fault **GEOLOGIC TIME AND EARTH'S BIOLOGICAL HISTORY** What is the geological time scale? o Divides up the history of the earth based on the life-forms that have existed during specific times MIDTERMS \| 9 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG since the creation of the planet. These divisions are called geochronologic units. o Example: ▪ Geo: rock ▪ Chronology: time o Divided by the following divisions: ▪ Erons -- next to longest subdivisions; based on the abundance of certain fossils. ▪ Eras -- next to longest subdivision; marked by major changes in the fossil record. ▪ Periods -- based on types of life existing at the time. ▪ Epochs -- shortest subdivision; marked by differences in life forms and can vary from continent to continent. What is the geological time scale, continued? o Due to the fact that early geologists had no way of knowing how the discoveries of the Earth were going to develop, geologist over time have put the time scale together piece by piece. Units were named as they were discovered. Sometimes unit names were borrowed from local geography, from a person, or from the type of rock that dominated the unit. o Example: ▪ Cambrian - From the Latin name for Wales. Named for exposures of strata found in a type-section in Wales by British geologist Adam Sedgwick. ▪ Devonian - Named after significant outcrops first discovered near Devonshire, England. ▪ Jurassic - Named for representative strata first seen in the Jura Mountains by German geologist Humboldt in 1795. ▪ Cretaceous - From the Latin "creta" meaning chalk by a Belgian geologist. o The earliest time of the Earth is called the Hadean and refers to a period of time for which we have no rock record, and the Archean followed, which corresponds to the ages of the oldest known rocks on earth. These, with the Proterozoic Eon are called the Precambrian Eon. The remainder of geologic time, including present day, belongs to the Phanerozoic Eon. o While the units making up the time scale are called geochronologic units, the actual rocks formed during those specific time intervals are called chronostratigraphic units. The actual rock record of a period is called a system, so rocks from the Cambrian Period are of the Cambrian system. o James Hutton ▪ a Scottish physician and geologist (1726-1797), thought the surface of the earth was an ever-changing environment and "the past history of our globe must be explained by what can be seen to be happening now." This theory was called "uniformitarianism," which was later catch-phrased as "the present is the key to the past." o William Smith ▪ a surveyor who was in charge of mapping a large part of England. He was the first to understand that certain rock units could be identified by the particular assemblages of fossils they contained. Using this information, he was able to correlate strata with the same fossils for many miles, giving rise to the principle of biologic succession. ▪ The principle pf biologic succession ❖ Each age in the earth‟s history is unique such that fossil remains will be unique. This permits vertical and horizontal correlation of the rock layers based on fossil species. MIDTERMS \| 10 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG ❖ Even though these two outcrops are separated by a large distance, the same rock layer can be correlated with the other because of the presence of the same shark teeth. This lets scientists know that the two layers were deposited at the same time, even if the surrounding rocks look dissimilar from each other. o During the early 1800‟s, English Geologist, Charles Lyell published a book called "Principles of Geology," which became a very important volume in Great Britain. It included all of Hutton‟s ideas, and presented his own contemporary ideas such as: ▪ The principle of cross-cutting relationships ❖ A rock feature that cuts across another feature must be younger than the rick that it cuts. ▪ Inclusion principle ❖ Small fragments of one type of rock but embedded in a second type of rock must have formed first and were included when the second rock was forming. o Charles Darwin ▪ 1809-1882 ▪ was an unpaid naturalist who signed up for a 5-yr expedition around the world aboard the H.M.S. Beagle. On this trip, he realized two major points. In spite of all species reproducing, no one species overwhelmed the Earth, concluding that not all individuals produced in a generation survive. He also found that individuals of the same kind differ from one another and concluded that those with the most favorable variations would have the best chance of surviving to create the next generation. ▪ The theory of natural selection was credited to Darwin (along with Alfred Russel Wallace) and he went on to write the famous "Origin of Species." Darwin‟s two goals in that work were: ❖ To convince the world that evolution had occurred and organisms had changed over geologic time. ❖ The mechanism for this evolution was natural selection. **PRINCIPLES BEHIND GEOLOGIC TIME** Nicholas Steno o a Danish physician (1638-1687), described how the position of a rock layer could be used to show the relative age of the layer. o He devised the three main principles that underlie the interpretation of geologic time: ▪ The principle of superposition - The layer on the bottom was deposited first and so is the oldest. ▪ The principle of horizontality -- all rock layers were originally deposited horizontally. ▪ The principle of original lateral continuity -- originally deposited layers of rock extend laterally in all directions until either thinning out or being cut off by a different rock layer. o These important principles have formed the framework for the geologic area of stratigraphy, which is the study of layered rock (strata). o Younger and Older Rocks ▪ Geologist studying the stratigraphy in the Copper Basin, Idaho. These rock layers were deposited horizontally, and uplifted later so they are now tilted at an angle (along the red arrow). o Decades later, other European scientists rediscovered „Steno‟s Laws‟ and began applying them. Abraham Gottlob Werner became famous for his proposal that all rocks came from the ocean environment. He and his followers were called "Neptunists." An opposing view (by Voisins) argued that all rocks of the earth came from volcanic environments. These scientist were called "plutonists." **RELATIVE AGE DATING** "relative age" means the age of one object compared to the age of another, not the exact age of an object. This method can only be used when the rock layers are in their original sequence. All six of the original stratigraphic principles may be applied to determine the age of a rock. This process is called age dating. Correlation of strata by rock unit type (lithology) or fossil type (biology) using species, composition, or texture leads scientists to extrapolate relationships over large areas of land. Because rock layers can be "matched up," we can guess that they were formed during the same period, so they usually are the same age. Using the principles of original horizontality and superposition, we can conclude that oldest rock is always on the bottom because is was deposited 1st. Deciphering the sequence of a rock outcrop is sometimes complicated by a features within the rock record called unconformities, which are specific contacts between rock layers. There are three types of unconformities that help us determine relative ages of rock layers: MIDTERMS \| 11 **EARTH AND LIFE SCIENCE** MR. JOHN GINEL LAYAG o Angular ▪ Horizontal beds are uplifted and tilted or eroded followed by new deposition of horizontal beds. The figure to the right is an angular unconconformity. o Disconformity ▪ Episodes of erosion or non- deposition between layers. o Nonconformity ▪ Sediment is deposited on top of eroded volcanic or metamorphic rock (indicates very long passage of time) Relative ages can also be determined using Lyell‟s principle of cross-cutting relationships. In the figure to the right, both the gray and the yellow horizontal strata needed to be in place for the pink layer to cut them, therefore, the pink layer is the youngest. Relative age dating with index fossils: o Biostratigraphy is the correlation of stratigraphic units based on fossil content. Biostratigraphically useful species are known as index fossils (or guide fossils) because they can be used as guides for recognition of chronostratigraphic units. o Index fossils are widespread, have short temporal durations resulting from rapid life spans, are abundant throughout their geographic and geologic ranges, and are easily recognized (unique). o Trilobites are a commonly used index fossil because they are easy to recognize. We know exactly when certain species became extinct, such that we can compare rock layers that contain trilobites with a second rock layer and, based on position, determine if the second rock layer is younger. o Fossils found in many rock layers have lived for long periods of time and cannot be used as index fossils. **ABSOLUTE AGE DATING** Absolute ages, or geochronometric ages, of rock can be assigned to the geologic time scale on the basis of properties of atoms that make up the minerals of a rock. Unlike relative dating, which relies on sequencing of rock layers (i.e. younger vs. older), absolute dating can produce an actual age in years. The number of neutrons in a nucleus of an atom determines the isotope of the element, just like the number of protons determines the identity of an element. Some isotopes are unstable and break down into other isotopes through a process called radioactive decay. Radioactive decay is characterized by beta decay, where a neutron changes into a proton by giving off an electron, and alpha decay, when isotopes give off 2 protons and 2 neutrons in the form of an alpha particle and changes into a new product. The original isotope is called the parent and the new isotope product is called the daughter. What is a half-life? o Each radioactive parent isotope decays to its daughter product at a specific and measurable rate. This measurement is reported in half-lives. The half-life of an isotope is the time it takes for 1⁄2 of the parent atoms in the isotope to decay. o If an isotope has a half-life of 4000 years, then after 4000 years 1⁄2 of the parent isotope remains. After another 4000 years, 1⁄2 of 1⁄2 remains, or 1⁄4 of the original amount of parent isotope. In another 4000 years (12,000 years total), 1⁄2 more of the remaining amount decays, so after 3 half-lives, there only remains 1/8 (1⁄2 of 1⁄2 of 1⁄2) of the original parent isotope. o If a scientist knows the half-life of the parent and measures the proportion of parent isotope to daughter isotope, he/she can calculate the absolute age of the rock. This valuable method is called radiometric dating. MIDTERMS \| 12