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Geologic Time Scale Originally based on relative age - revised with development of absolute age techniques - refined as new information becomes available. The geologic time scale is divided into: Eons Eras Periods Epochs

The Pre-Cambrian Supereon Composed of 3 Eons By end of Precambrian, organisms developing hard parts. Life believed to originate around the beginning of the Archean. Stromatolite, Archean bacteria

The Pre-Cambrian Supereon Geologic setting - First rocks formed are igneous - Crust formed through ‘differentiation’ - Earliest continental land masses form this way - Erosion ‘erases’ all land older than 3. 8 byo Life - Oldest fossils are 3. 5 byo (cyanobacteria microfossils) - Produced oxygen, poisonous to other bacteria - Atmospheric oxygen levels gradually increased; makes Cambrian explosion possible Climate - At end of Pre-Cambrian, glaciation kills almost all microorganisms

The Phanerozoic Eon (“visible life”) Divided into 3 Eras Cenozoic (“recent life”) Mesozoic (“middle life”) Paleozoic (“ancient life”)

The Paleozoic Era Divided into 7 periods Permian Pennsylvanian Mississippian Devonian Silurian Ordovician Cambrian Beginning of Cambrian period Explosion of life

Life in the Paleozoic Era First two periods (Cambrian & Ordovician) known as “age of invertebrates” – first marine organisms with shells show up at beginning of the Cambrian; commonly referred to as the “Cambrian Explosion” Middle of Paleozoic (Silurian & Devonian) known as “age of fishes” – also during this time, first land plants and first insects appear. Near end of Devonian, first amphibians e volve from fishes. Life is poised to move on to land. Late Paleozoic – amphibians are thriving, begin to see first reptiles.

Geology of the Paleozoic Era During the Paleozoic, there was much tectonic activity. In the Ordovician, Gondwana formed (Antarctica, South America, Africa, Madagascar, Australian, the Arabian Peninsula, and Indian subcontinent). This would later be joined with Laurasia (North American, Baltica, Siberia, Kazakhstania, & the North China and East China cratons. ) to form Pangaea. Time of mountain building – Appalachians formed, as well as mountains in what is now western Europe. This is thought to have caused significant climate change, which may have contributed to the extinction event at the end of the Paleozoic.

The Great Permian Extinction Occurred at the end of Paleozoic Era (marks the end of the Permian Period) Estimates that 90% of all marine species, 70% of all land species went extinct Possible causes: - Impact event - Volcanism - Methane gas emissions leading to climate change - Sea level changes

The Mesozoic Era Divided into 3 periods Cretaceous Jurassic Triassic

Life in the Mesozoic Era Mesozoic (“middle life”) is known as the “age of the dinosaurs. ” Dinosaurs ruled for over 100 million years. Pangaea continues its breakup during the early part of the Mesozoic. The Rocky Mountains and Himalayas form, the Atlantic Ocean basin widens, and the Indian Ocean forms. More coastlines mean more habitats. Also during this time, the first mammals, birds, and flowering plants appear. We also see crocodiles, turtles, and primitive mammals showing up in the fossil record of this era. On land, lush forests and swamps thrive, eventually producing large coal deposits along what is today the Gulf of Mexico, as well as parts of western North America. Towards the end of the Mesozoic, Pterosaurs become first

The Cretaceous Period Death in the Cretaceous A large asteroid or comet, approximately 10 km wide, slams into what is now the Yucatan Peninsula in Mexico. Firestorms rage, and the cloud of dust and debris that is ejected into the atmosphere causes cooling of the planet and a significant drop in photosynthesis. Estimates are that at least 60% of all life goes extinct, including the dinosaurs. But one group survives….

The Cenozoic Era Divided into 2 periods Quaternary Tertiary Further divided into 7 Epochs Holocene Pleistocene Pliocene Miocene Oligocene Eocene

Life in the Cenozoic Era In the Cenozoic, oceans flourish, insects thrive and diversify, mammal species increase as they take advantage of the niches left vacant by the death of the dinosaurs, large grasslands support ancestors of modern grazing land animals, Mastodons and Wooly Mammoths survive until the last ice age, large herds of horses, camels, and bison roam North America until about 12, 000 years ago , then go extinct.

Geology of the Cenozoic Era In the Cenozoic, the Atlantic basin opens further, continents move into position we see today, Rockies and Appalachians grow and are worn down, Alps and Pyrenees form, massive lava flows produce Columbian Plateau, Cascade mountain range forms, Colorado plateau raised several times, Colorado river cuts out Grand Canyon.

Climate in the Cenozoic Era Climate - Climate warm and humid at beginning - By mid-era, temperatures cool - Ice sheets cover Northern Europe, Siberia, Greenland, and Antarctica - At one point, one-fourth of all land covered by ice - Last major ice age ends around 11, 000 years ago

FOSSILS Peephole into the past…

fos • sil ( fä-səl) (From the Latin fossus, literally “having been dug up”) 1: a remnant, impression, or trace of an organism of past geologic ages that has been preserved in the earth's crust Fossils provide clues to organisms and their environments in Earth’s geologic past and are the basis for the geologic time scale. Scientists who study fossils are called paleontologists. However, fossils are very rare and only offer a limited view into the past.

Requirements for fossilization In order for an organism to become fossilized, it needs: Hard parts** – bones, shells, teeth, or wood Rapid burial – organism must be buried quickly in anoxic environment to avoid decomposition or decay. The longer an organism is exposed to oxygen after death, the more it will decay Conditions for fossilization are rare. Marine organisms dominate the fossil record because as they die, they sink to the bottom of the ocean and are buried by marine sediments. Terrestrial environments usually do not have conditions favorable for fossilization. **Some organisms without hard parts have been preserved as fossils, but as a general rule, the more hard parts an organism has, the greater the chance it will be preserved as a fossil.

HOW IS A FOSSIL FORMED? 1. Sediment An animal is buried by sediment, such as volcanic ash or silt, shortly after it dies. Its bones are protected from rotting by the layer of sediment.

HOW IS A FOSSIL FORMED? 2. Layers More sediment layers accumulate above the animal’s remains, and minerals, such as silica (a compound of silicon and oxygen), slowly replace the calcium phosphate in the bones.

HOW IS A FOSSIL FORMED? 3. Movement of tectonic plates, or giant rock slabs that make up Earth’s surface, lifts up the sediments and pushes the fossil closer to the surface.

HOW IS A FOSSIL FORMED? 4. Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people digging for fossils will expose the preserved remains.

Types of Preservation Permineralization Empty spaces in fossil are filled by minerals precipitated out of groundwater. Original structure of organism is preserved. Also known as “Petrification” (“turned to stone”) Petrified wood The Field Museum in Chicago displays a fossil of a Tyrannosaurus rex.

Types of Preservation Carbon Film Original organic material is preserved as a thin carbon film. Soft tissue can be preserved in this manner if conditions are just right.

Types of Preservation Molds and Casts A mold is the cavity left by the original shell after it dissolves. External mold of bivalve A cast is produced when that void is filled with sediment or minerals. Fern leaf fossil cast

Types of Preservation Original Remains In rare cases, the original tissue from an organism will be preserved. This can occur in various ways, such as through freezing, drying, entrapment in amber or tar, or burial in peat bogs. Insects trapped in amber Skull of Sabertooth tiger extracted from La Brea tar pits

Types of Preservation Original Remains In rare cases, the original tissue from an organism will be preserved. This can occur in various ways, such as through freezing, drying, entrapment in amber or tar, or burial in peat bogs.

Types of Preservation Trace Fossils The marks left by an organism in it’s environment, such as tracks, burrows, trails, nests, and droppings (known as coprolites).

Index Fossils Also known as guide or zone fossils – used to identify a particular geologic period. Index fossils come from species that were short-lived during a specific time period, very abundant, and found over a large geographic area. Lophophyllidium proliferum Pennsylvanian period Asaphiscus wheeleri, a trilobite from the Cambrian shale of Utah.

Ever date a fossil? Relative Age (AKA – Biostratigraphy) The geologic time scale was originally developed by determining the relative ages of rock layers in the Earth. The relative age was determined by comparing the fossils found in that layer with those in adjacent layers. This concept, known as the principal of faunal succession, states that fossils succeed each other vertically in a specific, reliable order over a wide horizontal area.

Ever date a fossil? Absolute Age (AKA – Geochronology) When molten rock cools to form an igneous rock, these radioactive elements are trapped inside. Over time, these radioactive elements decay into different, stable elements. Scientists use these known radioactive elements to determine the absolute age of a rock or rock layers by comparing the amount of radioactive elements to the amount of the related stable elements to determine the rocks age.

Laying down the law! The Principle of Original Horizontality and the Principle of Superposition Sedimentary rocks are composed of sediments originally deposited in a horizontal plane (Original Horizontality), with the oldest sediment on the bottom and youngest on top (Superposition). But alas, it’s not always this simple…

Uniformitarianism is the assumption that the same natural laws and processes that operate in the universe now, have always operated in the universe in the past and apply everywhere in the universe. “The present is the key to the past. ”

Fossils as record of life The fossil record shows life has become more complex and diverse over time

Matching Up Rock Layers — Correlation cor·re·la·tion [kawr-uh-ley-shuhn, kor-] noun 1. mutual relation of two or more things, parts, etc. Correlation is the process of matching similar layers of rock found in two or more different locations. Sedimentary rocks that date from the same age can be correlated over long distances with the help of fossils. Principle of Fossil Correlation - Strata (i. e. layers of rock) containing similar collections of fossils (called fossil assemblages) are of similar age. Also, fossils at the bottom of the strata are older than fossils closer to the top of the strata.

Matching Up Rock Layers — Evidence Used for Correlation For example, if the same Types of fossils were found in a limestone layer in two different places, it’s a good Indication that the limestone at each location is likely the same age, and therefore, one continuous deposit. There are times when one or more layers may be missing, due to erosion or non-deposition.

“Finding Clues to Rock Layers” 1) Study the rock layers and fossils at Sites 1 and 2. On a separate sheet of paper, write down the similarities and differences between the layers at the two sites. 2) List the kinds of fossils that are found in each rock layer of Sites 1 and 2. Complete the “Analyze and Conclude” section (questions 1 -9). You do not have to do the “More to Explore” activity

Make Observations about the fossils found in each layer. Column 1 Column 2 G Z F Y E X D W C B A

When you have completed the test, turn in your “Fossils” vocabulary and your geologic time wheel.

Layers of rock are said to be “conformable” when they are deposited in a sequence that has not been interrupted. This is rare, and most rock layers show some form of interruption. These interruptions, or gaps, in the rock layers are called Unconformities

“I REFUSE TO CONFORM!” When a rock or sediment layer is eroded away, and another rock layer is deposited on top of it, this becomes an unconformity, meaning there is a break in the sedimentary record. There are 3 basic types of unconformities: Disconformity Nonconformity Angular unconformity

Disconformities When there is layer missing from a geological sequence due to non-deposition or erosion, this is known as a disconformity. Because disconformities are found in parallel layers, they are sometimes difficult to spot.

Disconformity between Wingate and Chinle formations Wingate Chinle The sequence of events is as follows: 1 st - Subsidence and sediment deposition; 2 nd - Uplift and erosion; 3 rd - Renewed subsidence and deposition. In the picture above, the disconformity is indicated by an irregular black line between the 3 rd and 4 th rock unit from the bottom.

Nonconformities exists between sedimentary rock layers that have been deposited on top of pre-existing and older igneous or metamorphic rocks.

“The Great Unconformity”

Angular Unconformities An angular unconformity exists where horizontally parallel layers, or strata, of sedimentary rock are deposited on tilted and eroded layers that may be either vertical or at an angle to the overlying horizontal layers.

Angular Unconformity, Grand Canyon, Arizona. Angular unconformities - overlying and underlying rocks dip at different angles. Underlying rocks were tilted and eroded before the younger rocks were deposited.

Matching Up Rock Layers — Evidence Used for Correlation Geologists often can match up, or correlate, layers of rocks over great distances. Sometimes it’s possible to walk along the layers for kilometers and prove that it’s continuous.

Matching Up Rock Layers — Evidence Used for Correlation In other cases, the rock layers are exposed only where rivers have cut through overlying layers of rock and sediment.

Reading the rocks… “G” – deposited, then deformed, then eroded “S, H, L” – deposited “B” – lava intruded through the layers and formed extrusive layer on top of “L”

Reading the rocks… “S” layers deposited “F” layers were cut by fault Erosion, followed by deposition of “L”

Reading the rocks… “A” through “L” – deposited “H” – Igneous intrusion “D” – Igneous intrusion Erosion, “C”, followed by deposition of “S”

Somehow a "giant hotdog" also formed amongst the Hamburger Rocks in southern Capitol Reef National Park!

View of the Hamburger Rocks in the Halls Creek valley in Southern Capitol Reef National Park. A red layer of silty sandstone in the upper Navajo Sandstone(probably stream floodplain deposits) stand out in contrast to white sandstone (dune sand deposits) that makes up most of the formation.

Lab Handout

Read pages 150– 158 in “Cells and Heredity” Read pages 70 -77 in your Glencoe textbook “Clues to Earth’s Past” handout – Section 1 Define the following terms: - Fossil - Sedimentary rocks - Petrified fossils - Permineralization - Mold - Cast - Carbon film - Original remains - Trace fossils - Index fossil - Relative dating - Absolute dating - Half-life - Radioactive elements - Fossil record - Extinct - Gradualism - Punctuated Equilibrium - Principle of Superposition - Principle of Original Horizontality - Uniformitarianism - Unconformities - Disconformity - Nonconformity - Angular Unconformity - Eon - Era - Period - Epoch

The Cambrian Period Geologic setting - Oceans, shallow seas cover Earth - Six major continental land masses in southern hemisphere Life - Marine invertebrates, like trilobites, flourished - Preserved in fossil record because of their hard parts Climate - Mild, probably warmer than today

The Ordovician Period Geologic setting - Supercontinent Gondwana formed - Significant volcanic activity - Shallow seas uplifted Life - Marine blastoids, corals, snails, and clams first appear - Early land animals and plants Climate - By late Ordovician, oxygen levels decreased - More than 100 marine invertebrate families go extinct

The Silurian Period Geologic setting - Large glacial formations melt - Sea levels rise - Major mountain building events in NW Europe and eastern North America produce mountain chains Life - Tropical seas, coral reefs first appeared - Many changes in populations of fish - Wide rapid spread of jawless fish species Climate - Stabilized during Silurian

The Devonian Period Geologic setting - Three major continental land masses near equator - North America and Europe collide, produce Appalachian mountains - Much volcanic and earthquake activity Life - Amphibians among first land vertebrates - First wingless insects, first trees and forests appear in fossil record - Brachiopods, corals, and ammonites flourished Climate - Much like today - By end of Devonian, glaciation

The Pennsylvanian & Mississippian Periods Geologic setting - Shallow, warm marine waters flooded through continents and receded several times - Land masses move closer together - Uplifting of land along with formation of lowlands, deltas Life - Tropical swamp forests and terrestrial habitats widespread - Lizard-like amniot appeared – laid eggs on land - Led to evolution of birds, mammals, and reptiles on land Climate - More tropical and humid than today

The Permian Period Geologic setting - Pangea forms - Intense mountain building occurs - Interior portions of Pangea were dry, with miles of dunes Life - Mass extinction occurs at end of Permian - 90% of marine, 70% terrestrial species extinct Climate - Glaciers recede, climate becomes arid - Great seasonal changes and extreme temperatures - Along Pangea’s east coast, rain produces neartropical climates

Life in the Mesozoic Era Geologic setting - Pangea starts to fracture by mid-Triassic - Mountains form along west coast of North and South America - Continents much higher than sea level, no shallow seas - Volcanoes spewed out massive lava flows Life - First dinosaurs appear - First crocodiles, turtles, and small, primitive mammals appear Climate - Influenced by large tectonic events - Most of Earth was arid and dry

The Jurassic Period Geologic setting - Pangea rotates, breaks apart - Central Atlantic and Gulf of Mexico water basins form - Mountain building leads to uplift of Nevadan range Life - Abundant life forms, including great plant-eating dinosaurs - Stalked by vicious flesh-eating carnivores - Lush fern and cycad growths - Oceans full of fish, squid, and coiled ammonites - Pterosaurs, first vertebrates to adapt to life of flight Climate - Warm and dry, perfect for the animals of this period

The Cretaceous Period Geologic setting - Several smaller continents formed with extensive coasts - More coastlines = more near-shore habitats - Rocky Mountains and Alpine-Himalayan mountains form - Atlantic basin widens; Indian water basin forms Life - Hadrosaurs, or duck-billed dinosaurs common - Forests start to look more like modern forests - Ferns dominate dry lands, conifers dominate swamp lands - About 60% of species go extinct at end of Cretaceous - Caused by large meteor impact near Yucatan Peninsula