Earth Science (Second Quarter Exam Reviewer) PDF

GEOLOGIC  Erosion – process by which soil and PROCESSES weathered rocks are transported from one place to another.  Deposition – laying dow...

GEOLOGIC  Erosion – process by which soil and PROCESSES weathered rocks are transported from one place to another.  Deposition – laying down off sediments EXOGENIC PROCESSES carried by agent of erosion on  Exogenic Process – external process landforms/landmass.  Weathering – breaking of rocks and - Residual soil – it is a soil that remains other materials on the earth’s surface. on top of its parent rock or the rock from which it was formed. TWO TYPES OF WEATHERING - Transported soil – it is a soil that is 1. Mechanical Weathering – when rock moved to other places by wind, water, breaks without changing the chemical glaciers, and waves. composition. - Bedrock – the parent rock beneath the 2. Chemical Weathering – occurs when the residual and transported soil. chemical composition of rock is changed due to other substances. AGENTS OF EROSION 1. Wind – is the most active agent of MECHANICAL WEATHERING erosion in deserts, open fields, and - Temperature - happens due to cycle of beaches. heating and cooling.  Dunes – are mounds that are built by  Exfoliation – the repeated changes in wind consisting of loose sand. temperature cause the surface of the  Loess – is the deposit of fine sand and rock to peel off. silt. - Frost Action – a unique property of 2. Running Water – is one of the major water is that it expands when it freezes. agents of erosion. Examples are rivers, - Abrasion – this is the weathering off of streams, and runoff. rocks by solid particles carried by wind,  Runoff – is the rainwater that flows on water, and other agents. the surface and flows to the rivers and - Actions of living things – plants, streams. animals, and even human can cause  Oxbow lake – is a U-shaped body of mechanical weathering. water that forms when a river finds a different, shorter course. CHEMICAL WEATHERING  Alluvial fan – is a fan-shaped deposit - Hydrolysis (also known as water) – of gravel, sand, and even smaller pieces almost all chemical weathering is due to of sediments, such as silt, formed when action of water. stream flow suddenly slows down. (the - Oxidation (also known as Oxygen) – sediment is called alluvium) combines with other substances to form  Delta – is a landform created by the entirely new substance. deposition of sediments carried by a - Carbonation (also known as Carbon river as the stream flows to a lake or an dioxide) – combines with rain water to ocean. form a weak solution of carbonic acid.  Flood plain – is a flat area of land close - Acidification (Acid rain) – organisms to a river or stream. such as plants can also cause chemical weathering when they produce acid.   Levee – is a natural wall that blocks the weakening of supporting rocks caused water created by the deposit of large by heavy rain. particles.  Mudflow – is another type of mass 3. Waves – it constantly erode and shape wasting that usually occurs after a the shoreline. heavy rain.  Shoreline – is where the body of water  Slump – is the downward sliding of a and land meet. mas of rock or unconsolidated material  Beaches – consist of fine sand or large along a curved surface. pebbles that are carried by waves to the  Debris flow – involves the flow of soil shores of seas and lakes. containing large amount of water along  Sandbars – are submerged or partly a downward slope. exposed ridge of sand or coarse  Creep – is the slow type of mass sediment that is built by waves offshore wasting that involves the gradual from a beach. downhill movement of soil caused by  Spits – are elongated ride of sand that the alternative expansion and stretches from the land to the mouth of contraction of the surface due to a nearby bay. freezing and melting, or wetting and 4. Glaciers – erode surfaces through drying. abrasion.  Moraine – is the accumulation of dirt ENDOGENIC PROCESSES and rocks that have fallen onto the  Endogenic Processes – the processes that glacier surface or have been pushed happen inside the Earth. along by the glacier as it moves.  Earth’s core – 6000 degrees Celsius  Drumlin – is an elongated hill with the shape of an inverted spoon or half- THE HEAT IN THE EARTH’S buried egg, which is formed by glacial INTERIOR COMES FROM ice acting on underlying unconsolidated sediments or ground moraine. THREE DIFFERENT SOURCES  Meltwater deposits – are sediments 1. Heat that was left during the formation of carried and deposited along the the Earth, meltwater streams, which are formed 2. The gravitational pressure on the core when glaciers start to melt. caused by the tidal forces of the Sun,  Iceberg deposits – are rocks and Moon, and other planets and the rotation sediments that are picked up from land of the Earth, and and deposited on the ocean floor by 3. The radioactive decay of elements in the melting icebergs. core.  Glacial lake – is a lake created by melted glacier.  Earth – it was formed around 4.5 billon 5. Mass Wasting – occurs when gravity years ago. pulls rocks and soils down the slopes  Immense pressure – the combined tidal  Talus (accumulated sediments) – the pressure and rotation of the Earth cause rock debris that settles at the base of the the core to be under this pressure. slope.  Nuclear fission of heavy elements in the  Landslide – is an example of mass Earth’s interior – is the last and most wasting that can be caused by an important source of heat. (occurs in form earthquake, volcanic eruption, or of radioactive decay)  Magma – is an extremely hot and viscous  Recrystallization – is the process by mixture of molten and semi-molten rocks which crystals are packed together that originates from the lower part of the creating a new crystal structure. earth’s crust and upper portion of the  Neometamorphism – is a process that mantle. results in the formation of new minerals - It can create new landforms and cause (this process is sometimes called physical and chemical changes in neocrystallization means “new crystals”) different environments. Low Grade  High Grade  Decompression Melting – is a process in Slade – Phyllite – Schist – Gneiss - Magnetite which magma forms due to decreased rock pressure. CAUSES OF METAMORPHISM  Heat Transfer – can also form magma 1. Increase in Temperature when hot liquid rock pushes itself to  Temperature increase can be caused by earth’s cold crust. layers of sediments being buried deeper  Flux Melting – occurs when solid rock and deeper under the surface of the Earth. melt into magma through the addition of  As we descend into the earth, the water or other volatiles, causing rocks to temperature increases about 25 degrees melt at lower temperature. Celsius for every kilometer that we descend. The deeper the layers are MAGMA FORMATION buried, the hotter the temperatures  Pluton – happen when a crystallized become. The great weight of these magma is found beneath the Earth’s curst. layers also causes an increase in pressure,  Tephra or volcanic ash – happen when which in turn, causes an increase in the ejected magma solidifies in the air to temperature. form volcanic rock.  Fissures – are cracks that may become 2. Increase in Pressure volcano.  There are 3 factors that cause an increase - Magma cools and crystallize to form in pressure which also causes the igneous rock formation of metamorphic rocks. These - Igneous rock undergoes weathering (or factors are; break down) to form sediments. a. The huge weight of overlying layers of - The sediments are transported or sediments. deposited somewhere (such as the b. Stresses caused by plates colliding in beach or in a delta, or in the deep sea). the process of mountain building. c. Stresses caused by plates sliding past each other, such as the shearing stresses METAMORPHISM at the San Andreas fault zone in (Internal process of the earth) California  Metamorphism - change in mineral 3. Chemical Changes composition and texture of a rock that is  Factors that cause chemical changes in subjected to high temperature and rocks also contribute to the formation of pressure within the earth. metamorphic rocks. TYPES: Regional and Contact  Very hot fluids and vapors can, because INVOLVES TWO PROCESSES: of extreme pressures, fill the pores of Recrystallization and Neometamorphism  existing rocks. These fluids and vapors DEFORMATION OF EARTH’S can cause chemical reactions to take CRUST place, that over time, can change the 1. Stress chemical makeup of the parent rock. TYPES a) Compression – squeezes the rocks in TYPES OF METAMORPHISM the curst. 1. Contact Metamorphism b) Tension – pulls on the rocks of the  This occurs when magma comes in crust causing them to stretch over a contact with an already existing body large area. of rock. c) Shearing – pushes the rocks in the crust  When this happens, the existing rock to opposite directions causing them to temperature rises and becomes twist or tear apart. infiltrated with fluid from the magma.  Joints – fractures have not moved. They  The area affected by the contact of are cracks that are parallel to one another. magma is usually small, from 1 to 10  Blocks – form where the different sets of kilometers. joints cross one another.  Contact metamorphism produces nonfoliated (no cleavage.) rocks such as 2. Folding – is an effect of compressional marble and quartzite. stress. Some rocks do not break when under stress. Instead, the rocks break or 2. Regional Metamorphism crumple.  This metamorphism produces rocks TYPES such as gneiss and schist. a) Anticline  Regional metamorphism is caused by b) Syncline large geologic processes such as - A bend in the rock is called a fold. mountain building. - An upward fold is called anticline and  These rocks when exposed to the the downward fold, syncline. surface show the unbelievable pressure - Large folds form folded mountains. that cause the rocks to be bent and  Plateau – can also be formed by folding. broken by the mountain building process. 3. Faulting – is the breaking of rocks along  Regional metamorphism usually a crack or fracture when rocks can no produces foliated rocks such as gneiss, longer withstand stress. schist and slate. (have a layered or banded - When the rocks move along a break or appearance.) crack, a fault is created. - Faults may be in the form of normal, 3. Dynamic Metamorphism reverse, and strike-slip faults.  This also occurs because of mountain TYPES building. These huge forces of heat a) Normal Fault – is characterized by a and pressure cause the rocks to be rock on one side of the fault that is bent, folded, crushed, flattened, and lower relative to the other fault. sheared. (tension) - Mountains that are formed by blocks of rocks uplifted by normal faults are called fault-block mountains.  b) Reverse Fault – is characterized by a CONTINENTAL DRIFT THEORY rocky block that is pushed up relative  Alfred Wegener to the rock on its side. (compression)  States that “continents are constantly moving”  Pangaea – Laurasia – Gondwanaland – Present I. 225 Million Years Ago (Pangaea) c) Strike-Slip Fault – results when the II. 150 Million Years Ago (Laurasia and adjacent blocks of rocks move Gondwana) sideways and not up and down. III. 100 Million Years Ago (Asia, Europe, (shear) Australia, Africa, North America, South America, Antarctica) IV. Earth Today SEAFLOOR SPEADING  New crust is created by the intruding magma as the plates move apart. Lava erupts on the ocean floor.  Introduced by Harry Hess and Robert Dietz. PLATE TECTONICS  “hot and less dense material from the mantle rises to the surface along the mid- BOUNDARIES ocean ridges. This material flows 1. Convergent sideways pushing the seafloor away from the ridges in both direction”.  As the oceanic crust moves away from the mid-ocean ridges, it cools, contracts and becomes denser. This crust helps in the formation of the ridge. Because of continuous formation of magma in the 2. Divergent crust, the result is the widening of the ocean floor.  Convection Currents – it is the one that causes the magma to rise OCEAN BASIN 3. Transform EVOLUTION OF OCEAN BASIN 1. Embryonic  Continents are starting to separate resulting in the formation of rift valleys. Example: Great Rift Valley in Eastern Africa 2. Juvenile Structure of Ocean Basin  Seafloor basalts begins forming as 1. Continental shelf – continental landmass continental margins separate. that is covered by the sea.  Rift valleys deepens and is flooded by 2. Continental slope – edge of the seawater. continental shelf where the seafloor  Mid ocean ridge is formed. suddenly drops. Example: Red Sea 3. Continental rise – located at the base of continental slope. Sediments that move 3. Mature down from the continental shelf pile up at  Broad ocean basin widens, trenches the base of the slope and is gently develop, and subduction begins. sculptured by slow moving current.  Ocean basin with spreading center and 4. Abyssal plain – characterized by a vast continental margins are prominent expense of terrain that is flat, cold, and features. dark since light can no longer penetrate Example: Atlantic Ocean through this depth. 4. Declining  Deep ocean trenches – are the deepest  Subduction narrows much of the parts of the ocean. seafloor and oceanic ridge due to converging tectonic plates. DIVERGENT BOUNDARY – move apart Sea-Floor oceanic-oceanic (o-o) New Ocean Crust  Results in the formation of trenches, Spreading volcanic island arcs, and coastal mountain Mid-Ocean oceanic-oceanic (o-o) Underwater ranges. Ridge Mountain Rift Valley continental-continental (c-c) Volcanoes/New Example: Pacific Ocean Land 5. Terminal When plates become stretched, fissures appear, and the crustal block collapses downward.  Ocean basin becomes narrow and becoming shallow due to sedimentation.  Young mountain ranges are formed CONVERGENT BOUNDARY – come together along the sides. Mountains continental- Mountains Example: Mediterranean Sea continental created Can fold or form faults on the crustal rocks. This process forms mountains and mountain ranges. 6.Suturing  Also referred as Continental Collision.  The remaining seafloor is eliminated. SUBDUCTION ZONES Deep-Sea oceanic-continental Depression (hole  Continents collide forming a continental Trench in the ground) mountain chain. Volcanic Arc oceanic-continental A line of Example: Himalayas volcanoes on land Island Arc oceanic-oceanic A line of islands in the ocean At the convergent plate boundaries, oceanic crust go under another plate and sink into the asthenosphere. The sinking plate melts and turns into magma which then gives rise to new volcanoes and volcanic island arcs. TRANSFORM BOUNDARY – slide past each other Faults All types Earthquakes/Tsunamis  DATING THE EARTH RELATIVE DATING  A method of showing the sequence of events, that is, which happened first, next Determining the age of the Earth and so on.  Aristotle - Greek philosopher (384-322  When you give the age of a rock or fossil BC) thought that Earth has been in compared to another rock or fossil. perpetual existence.  An actual age in years is not determined  Lucretius - Roman Poet (99 BC to 55 BC), believed that Earth had not existed STRATIGRAPHY for a long time based on the absence  Study of strata, or sedimentary layers. accounts prior to the Trojan War.  James Ussher - of Ireland, who believed  Strata – sedimentary layers that the time of creation of Earth was  graphy – descriptive science 4004 BC. - is the method of sequencing geological  Nicolas Steno - in the 1660s, a Danish events based on the arrangement of the anatomist and priest, formulated the rock strata (layers of rocks) without modern concepts of deposition of providing numerical dates horizontal strata.  James Hutton - in the 1700s, a Scottish geologist, proposed the principle of uniformitarianism which states that physical, chemical, and biological processes that work today are the same forces that have worked in the geological past. - You have to understand the different geologic events that are occuring at present. “The present is the key to the past.” Principles of Relative Dating 1. Principle of Superposition  Geologic Dating – a technique to - Is an undisturbed sequence of stratified determine the age of the rocks; either its rocks, each layer is older than the one exact numerical age (ABSOLUTE above it and younger than the one below DATING) or its age as compared to the it. other rocks (RELATIVE DATING). 2. Principle of Original Horizontality - Sediments are originally deposited horizontally due to gravity. - Some layers are deformed or disturbed (tilted or folded) after formation - This is important in analyzing folded or tilted strata  record exists in that place. The lost 3. Principle of Lateral Continuity record may involve hundreds of millions - It states that if layers are deposited of years horizontally over the sea floor, then they would be expected to be laterally continuous over some distance. - Sedimentary rocks are laterally continuous over large areas 3 TYPES OF UNCONFORMITIES 1. DISCONFORMITY - missing parallel rock layers- younger. Erosion takes place here and removes the younger top layer, deposition will happen again 2. ANGULAR UNCONFORMITY – tilted 4. Principle of Cross-cutting Relationship or folded sedimentary rocks younger - A fault, dike, or magma intrusion is 3. NONCONFORMITY – igneous or always younger than its surrounding metamorphic rocks found below rocks. sedimentary rock. 5. Principle of Inclusion - Any rock fragments included in a rock must be older than the rock in which it is included 6. Principle of Unconformities - Layers of sedimentary rocks are conformable if they were deposited without interruption. - An unconformity represents an interruption in deposition, usually of long duration. - During the interval when no sediment was deposited, some rock layers may have been eroded - Thus, an unconformity represents a long- time interval for which no geologic   Paleontologist - Scientist who study fossils  Fossils - These are remains of extinct plants and animals embedded in sedimentary rocks INDEX FOSSILS  Index or Guide Fossils – organisms that existed for a short period of time, then went extinct. e.g. Brachiopods, Ammonite, Trilobite TO BE CONSIDERED AN INDEX FOSSIL, IT MUST MEET 3 CRITERIA: 1. The fossilized organism must be easily recognizable. It must be easy to ID and look unique. 2. The fossils have to be geographically widespread, or found over large areas so that we can use them to match layers separated by huge distances. ABSOLUTE DATING 3. The fossil must have lived for only a  Sometimes called numeric dating short time, so that it appears in only  Gives rock an actual date or date range in horizontal layer of sedimentary rocks. number of years  Radioactive minerals in rocks are used as geological clocks.  A half-life is the time needed for one-half of the parent atoms to turn into daughter atoms.  GEOLOGIC TIME Significant Events - Ubiquitous Active Volcanism Resulting SCALE in Worldwide Magma Ocean and Asteroid Bombardment.  The geologic time scale is a timeline that - Moon formation divides Earth's history into units - Continental and oceanic crusts began to representing specific intervals of time that solidify cover geologic events and significant - 3.8 billion years ago developments in the evolution of life.  Eons - largest intervals of geological time Archean Eon (4 - 2.5 billion years ago) with duration of hundreds of millions of  Single-celled organisms, such as blue- years. It is divided into four eons: green algae, archaeans, and bacteria first ➔ Hadeon eon appeared. ➔ Archeozoic eon  It is the beginning of free oxygen in the atmosphere ➔ Proterozoic eon ➔ Phanerozoic eon Significant Events - Presence of Stromatolites - Existence of Unicellular Organisms  Eons are divided into smaller time - Beginning of the Free Oxygen in the intervals known as eras. Eras are then Atmosphere subdivided into periods.  Epochs are the smaller subdivisions of the Cenozoic era. Proterozoic Eon (2.5 billion to 542 million years ago)  During this eon, the first continents PRECAMBRIAN PERIOD appeared. ➔ Hadeon eon  The Proterozoic Eon is marked by the ➔ Archean eon appearance of multicellular animals like ➔ Proterozoic eon sponges and the mass extinction of these  The Precambrian period spans 4 billion organisms. years, or about 88% of the total lifespan Significant Events of Earth. - Biological activity allowed atmospheric Major events oxygen levels to increase - Moon’s formation - Unicellular eukaryotic life evolved - Filling of ocean basins - Appearance of multicellular organisms - First evidence of life and their mavs extinction. (Charnia, - Beginning of plate tectonics Kimberella, Dickinsonia, and Spriggina.) - Formation of the continents - Continents merged into a single - Oxygenation of the atmosphere landmass called Rodinia - 1.1 billion years ago Hadean Eon (4.5 - 4 billion years ago) - Nuna - 1.8 billion years ago  Known as the rockless eon. No rocks from the Hadean Eon exist today on Earth except for meteorites.  Earth was molten and it would only solidify as it cooled. 800 million into the earth’s history.  Phanerozoic Eon (542 million years - Primitive fishes ago) - Seaweed  The first life forms with parts, such as - Fungi shells, scales, and bones and teeth,  Graptolites, bryozoans, gastropods, appeared during the Phanerozoic eon. bivalves, and echinoids were dominant.  The fossils of these life forms are great  Global cooling, glaciation, and frequent tools in the study of history of the volcanic activities were observed. Phanerozoic eon.  North America went under shallow seas. ➔ Paleozoic Era The period ended in huge extinction due to glaciation. ➔ Mesozoic Era ➔ Cenozoic Era A. Paleozoic Era (541-252 million years 3. Silurian Period ago)  The Caledonian mountains of  The supercontinent Pangaea was formed Scandinavia rose, and coral reefs were during this era. formed. Laurasia: North America, Europe, and  Emergence of insects, jawed fishes, large Siberia. reefs, vascular plants appeared on land Gondwana: South America, Africa, such as cooksonia, a primitive terrestrial Australia, Antarctica, India, and parts of plant. China.  A rise in sea levels occurred worldwide. First jawed fishes and arthropods 1. Cambrian Period - Insects  This period is the beginning of the - Centipedes Paleozoic era, during which shallow seas - Millipedes covered parts of the continents and a mild climate existed.  Known as the “Age of Trilobites”. 4. Devonian Period  Acadian mountains of New York rose  Rodinia began to break into smaller during this period, and the erosion of continents. mountains resulted in the deposition of  The mass extinction of trilobites and much sediment in seas. nautiloids may have been caused by  Known as the “Age of Fishes”, fishes and glaciation. terrestrial plants became abundant and Marine invertebrates diverse. - Shellfish - First Amphibians - Echinoderms - First Land Plants - Trilobites  Mass extinction event occurred near the - Brachiopods end of the Devonian Period which was - Mollusks probably due to glaciation or meteorite impact. 2. Ordovician Period  Many volcanoes and mountains formed 5. Mississippian Period during this period. New organisms take  The Appalachian Mountains of North on different forms (Diversification). America were formed during this period. - Corals  Ice covered large areas of the earth, and 1. Triassic Period swamps covered the lowlands.  Rise of Diapsid reptiles who survive the  The first winged insects appeared. Permian extinction, mammals, and flies. The Palisades of New Jersey and the 6. Pennsylvanian Period Caucasus Mountains of Russia were  The first reptiles, ferns, mayflies, and formed. cockroaches appeared during this period. - Dinosaurs - Mammals 7. Carboniferous Period - Crocodyliformes - Highest oxygen content - Mollusks (dominant invertebrate) - Abundant Forest - Reptiles like turtles and ichthyosaurs - First reptiles  The triassic period ended with an extinction event, the end-Triassic 8. Permian Period extinction event, which may have been  The Ural mountains of Russia rose this caused by volcanic eruptions that led to time. Known as the “Age of global warming and ocean acidification. Amphibians,” amphibians and reptiles dominated this period. 2. Jurassic Period  Gymnosperms were the dominant plants.  Existence of dinosaurs, angiosperms, - First stoneflies feathered reptiles, marine reptiles, and - True bugs - Beetles birds. The Rocky Mountains rose during - Caddisflies appeared this period and the volcanoes of Western  Formation of Pangaea North America were active. Dinosaurs  Dry Climate including the giant-lizard hipped  Age of Amphibians dinosaurs, roamed the earth. The first  Permian Mass Extinction flowering plants also evolved this time.  The permian period ended with the Minor extinctions that occurred 190-160 largest mass extinction. Trilobites went million years ago. extinct, together with all animal families, almost all marine species, and many trees 3. Cretaceous Period caused by glaciation or volcanism.  Separation of Gondwana and Laurasia, Emergence of Flowering Plants and B. Mesozoic Era (252-66 million years Placental Animals. Raging tectonic and ago) volcanic activities occurred during the  The breakup of the supercontinent Upper Cretaceous Period. A minor Pangaea occurred during this era. extinction occurred about 82 million Mesozoic means “middle animals.” years ago that could have been caused by Dinosaurs lived during this era. Except an asteroid impact or volcanic activity, for birds, dinosaurs became extinct at the and ended with the large extinction of end of the Cretaceous period. dinosaurs, pterosaurs, ammonites, and - Triassic Period species of marine invertebrates. - Jurassic Period - Cretaceous Period C. Cezonoic Era (66 million years ago)  Age of Mammals. It is the most recent of the three major subdivisions of the Phanerozoic eon. This era could have  been called the “Age of Flowering a) Miocene Epoch Plants,” or the “Age of Insects.”  Was characterized by a warmer climate - Paleogene Period compared to the oligocene epoch. Kelp - Neogene Period forests and grasslands first appeared. - Quaternary Period About 95% of the modern seed plants  After a large asteroid collided with Earth were already present. 65 million years ago, the dinosaurs were replaced by the mammals as the most b) Pliocene Epoch dominant group.  Was marked by a cooler and more arid climate compared to the Miocene epoch. 1. Paleogene Period Australopithecus was thought to have - Paleocene Epoch evolved in this epoch. An event during - Eocene Epoch this epoch was the collision of the - Oligocene Epoch tectonic plates of India and Asia, which  Major extinction event called the “Great resulted in the formation of the break in continuity” Ice Age + Himalayas. Continental Drift. 3. Quaternary Period a) Paleocene Epoch  Pleistocene Epoch and Holocene Epoch.  Began with the mass extinction event at the Cretaceous-Paleogene (K-Pg) a) Pleistocene Epoch Boundary and ended with the Paleocene-  Was characterized by global cooling, also Eocene Thermal Maximum. known as the ice age. The temperature zones of the world were covered by b) Eocene Epoch glaciers. Many species of plants, birds,  Major division of the geological time and mammals present today were already scale. It ended with the major extinction in existence. Homo sapiens spread out event called the “Great break in worldwide. continuity” b) Holocene Epoch c) Oligocene Epoch  Earth at present. It is characterized by a  Comes from the Greek words oligos warm period. Anthropocene epoch or the meaning “few” and kainos meaning “Age of Man.” During this epoch, the “new”, refers to the sparse extant forms recorded history of man existed. During of the molluscs during this epoch. It is this time, humans developed marked by the continuous drifting of the technological advancements that enabled continents to their present day positions. them to better understand the world. 2. Neogene Period  Fossils - remains or traces of an organism  Miocene Epoch and Pliocene Epoch. preserved in sedimentary rocks from the Australopithecus was thought to have geological past. evolved in this epoch.  Paleontologist - scientist who study fossils.  True Form Fossils - actual remains that did not change through time.  Petrified Fossils - fossils that turned into stone were formed when all part of an organism were replaced by minerals.  Molds and Cast - preserve the form and shape of the organism.  Carbonized Fossils - result from a process undergone by leaves and delicate animal forms, through which they were covered with fine sediments.  Amber - hardened resin of ancient trees where insects are preserved.  Index Fossil - organisms that existed for a short period of time, then went extinct. TO BE CONSIDERED AN INDEX FOSSIL, IT MUST MEET 3 CRITERIA: 1. The fossilized organism must be easily recognizable. 2. The fossils have to be geographically widespread, or found over large areas so that we can use them to match layers separated by huge distances. 3. The fossil must have lived for only a short time, so that it appears in only horizontal layer of sedimentary rocks.