ES 9, 6c, 7a UNIT 8/9: GEOLOGIC TIME AND VIRGINIA GEOLOGY

What is a Fossil? The history of the Earth and ages of rocks can be investigated and understood by studying rocks and fossils found within sedimentary rocks. A fossil is the remains, impression or other evidence preserved in rock of the former existence of life.

Fossils Fossil evidence indicates that life forms have changed and become more complex over geologic time. Some ways in which fossils can be preserved are Molds Casts Original remains Petrified Carbon films

Types of Fossils Organisms buried in sediment may decay or dissolve away leaving a cavity or mold. If the space is subsequently filled with sediment, an external cast can be made. Molds and casts are three dimensional and preserve the surface contours of the organism.

Types of Fossils Original Remains: All or part of an organism becomes encased in amber, ice, or tar preserving the organism

Types of Fossils Petrification A fossil in which minerals fill the cells of an organism (ex. wood, bone, etc.). This process is called petrifaction = “turned into rock”. Trace Fossils Preserved evidence of the activities of ancient organisms (footprints, burrows, etc.)

Types of Fossils Carbon films All living things contain an element called carbon. When an organism dies and is buried in sediment, the materials that make up the organism break down. Eventually, only carbon remains. The thin layer of carbon left behind can show an organism’s delicate parts, like leaves on a plant.

Index Fossils A fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found Index fossils can also be used to correlate rock layers

Unit 8 Part 2: Relative & Absolute Dating

Finding Out How Old Rocks Are We are going to determine the age of rocks in two ways: 1.Relative Time = puts events in the sequence of their occurrence, but does not identify the actual date. ➢ Example: Mrs. Weathersee was born after Jaws was released into theaters but before The Return of the Jedi was into theaters 2. Absolute age = measuring the actual age of the rock using various techniques.

Uniformitarianism - a principle that geologic processes that occurred in the past can be explained by current geologic processes Hutton theorized that the same forces that change Earth’s surface now, such as volcanism and erosion, are the same forces that were at work in the past. If it takes 10 years to erode 1 meter of this mountain today... That’s how long it would have taken a long time ago.

Law of Original Horizontality To understand this we must first learn some laws associated with correlating rock age. 1) Sedimentary rocks are usually deposited in horizontal layers W L QAQA K A P V Z

Law of Superposition 2) In a sequence of undisturbed sedimentary rock layers, the oldest rocks will be at the bottom & the youngest at the top.

Law of Cross-Cutting Relationships 3) Igneous intrusions or faults are younger than the rocks it intrudes or cuts across ➢ Intrusions occur when magma rises up from deep within the earth and burns into the rock. ➢ Cross-cutting Features: ➢ Sill – an igneous pluton that is horizontal to the bedding plane of the sedimentary rocks it intrudes. ➢ Dike - an igneous pluton that is vertical to or cuts across the bedding plane of the sedimentary rocks it intrudes. ➢ Stock and Batholith- huge units of rising magma that cuts into rock.

Laccolith- a bulge of magma between sedimentary rock layers that is fed by a dike.

Examples of plutons showing intrusive relationships. ➢ Diagram (1): Rock A, Dike B, Erosion surface C, Rock D Oldest  Youngest ➢ Diagram (2): Rock A, Sill B, Dike C Oldest  Youngest ➢ Diagram (3): Rock A, Stock B, Dike C Oldest  Youngest

(1) Normal fault (2) Reverse fault Examples of faults to illustrate cross-cutting relationships. (1) Unit A is the oldest, followed by B and C. Fault D is the youngest. (2) Unit A is the oldest, followed by B and C. Fault D is younger than unit F & E. F Fault – A break in rock layers.

☞ D is the oldest rock layer because it gets cut across by everything. ☞ C is the next oldest because it gets cut across by B and cuts through D ☞ B is the next oldest because it gets cut across by a and cuts through C and D ☞ A is the youngest because it cuts across everything. __________, __________, __________, __________ Oldest  Youngest

F is younger than D, C, and B because it cuts across them, but older than A because it doesn’t cut across it. E is the youngest rock because it cuts across all others. The rocks are currently being eroded on the surface. ______, ______, ______, ______, _____, ______ Oldest  Youngest DCBFAE ______, ______, ______, ______, _____, ______ Oldest  Youngest

Which is oldest: X, T, K, or H? H Which is youngest? X

Which formed first: the S layers or the fault that goes through them? S

Folds are bends in rock that form when rock is put under stress, usually when two continents collide together. Which happened first: the rock layers or the folding of them? The rock layers

Sometimes the folds get eroded away and you only see tilted rock layers. Which happened first: the rock layers A –E or the tilting of those rocks? Rocks A-E and they were originally horizontal.

Law of Included Fragments 4) The pieces of one rock found in another rock must be older than the rock in which they’re found Ex. Conglomerate The clasts in this conglomerate were already formed before the actual conglomerate formed. It was weathered, eroded, deposited and lithified before it became a conglomerate.

The dark pieces found in the lighter rock layers are older than the layer they are in.

What existed first: the little pieces of rock within rock layer S or rock layer S? The little pieces within S

Unconformities Unconformity = a place in the rock record where rock layers or parts of rock layers are missing from erosion. There are three main types 1) Angular Unconformity 2) Disconformity 3) Nonconformity

1. ANGULAR UNCONFORMITIES Angular unconformities are characterized by an erosional surface is between (cuts into) folded or dipping (tilted) strata and horizontal layers. Overlying strata (layers) are deposited basically parallel with the erosion surface. Erosional surface e01.cfm?chapter_no=visualization

2. DISCONFORMITIES Disconformities are characterized by an irregular erosional surface which is between flat-lying sedimentary rocks. Erosional surface Watch:

3. NONCONFORMITIES Nonconformities are characterized by an erosional surface which truncates, or cuts off, igneous or metamorphic rocks. The nonconformities are between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock. Erosional surface

Nonconformities happen when an igneous intrusion is exposed and weathered and eroded. Where is the nonconformity?

Geologic history Surface Erosion (youngest) ______F_________ ______J__________ ______B_________ ___Erosion A______ _____R__________ _____S__________ _____M__________ ______K _________ _____P___(oldest) MPMP Geologic history Surface Erosion (youngest) ________________ __________(oldest)

B D J T P G Z X F L E A Q Erosion A Geologic history Surface Erosion (youngest) ____B_______ ____F______ ____Z_______ __Erosion A__ __Folding____ __G_________ __X_________ __P_________ __T_________ __Q_________ __D_________ __E_________ __A_________ __L___(oldest) Geologic history Surface Erosion (youngest) ___________ __________ ___________ __Folding____ ___________ _____(oldest)

F C C F G B B Erosion Z Fault R G E E H Geologic history Surface Erosion (youngest) __A_________ ___D_________ __Erosion Z____ ___Fault R____ ___H_________ ___C_________ ___F_________ ____G________ ____B________ __E___(oldest) G H F E B A D C Geologic history Surface Erosion (youngest) ___________ ____________ _____(oldest)

Erosion P D Folding Z Geologic history Surface Erosion(youngest) __G________ __B________ __D________ __E________ __A________ _Erosion P___ __Folding Z__ ___C_______ ___F_______ __H__(oldest) A E CB F H G Geologic history Surface Erosion(youngest) __________ ____(oldest)

Absolute Dating Radiometric Dating techniques use naturally-occurring radioactive isotopes Isotope -- form of an element that has additional neutrons Radioisotope -- isotope that spontaneously decays, giving off radiation Rate of Radioactive Decay Radioisotopes decay at a constant rate. Rate of decay is measured by half-life Half-life -- time it takes for one-half of the radioactive material to decay. Decay products Radioisotopes may decay to form a different isotope or a stable isotope. May be a series of radioactive decays before a stable isotope is formed. Stable isotope is called the "daughter" formed from decay of radioactive "parent.”

Absolute Dating Radiometric Age Dating Radioisotopes are trapped in minerals when they crystallize. Radioisotopes decay through time, and stable isotopes are formed. Determining the ratio of parent isotope to daughter product reveals the number of half-lives that has elapsed. Common isotopes used in age dating Uranium to Lead -- half-life of U-238 is 4.5 b.y. Carbon half-life of C-14 is 5730 yrs

Unit 8 Part 3: Geologic Time Scale

Geologic Time Scale – a timeline of Earth’s 4.6 billion year old history divided into periods of time by major events or changes on Earth What do we call these major events or changes? Geologic Time Scale

Catastrophic Events – events that cause major destruction or change life completely Examples: Mass extinctions Ice Ages Meteors Major volcanic eruptions Catastrophic Events

1. Hadean 2. Archean 3. Proterozoic 4. Phanerozoic 1-3 make up Precambrian Time EONS – largest division of time Eons of Time:

AMOUNT OF TIME: 90% of Earth’s history Lasted nearly 4 billion years of Earth’s 4.6 billion year total MAIN EVENTS: Volcanic ash & dust → clouds formed → rain Single-celled micro-organisms in ocean towards the end NO animals! NO plants! PRECAMBRIAN TIME

Explosion of Life! Contains 3 Eras: Paleozoic Era – “Age of Fish” Mesozoic Era – “Age of Reptiles” Cenozoic Era – “Age of Mammals” Phanerozoic Eon – 544 million years ago → present day

544 mya – 248 mya All life in ocean until amphibians developed Reptiles, Insects, Ferns developed → life moving onto land Ends with a Mass Extinction possibly from a meteor strike – kills 90% of all ocean species! Paleozoic Era = “Ancient”

248 mya → 65 mya Dinosaurs Rule! Small mammals, birds, and flowering plants Ends with Mass Extinction due to meteor strike off Mexico Dust cloud blocked sunlight, killed plant life and affected food chain Mesozoic Era = “Middle”

65 mya → Present Large warm-blooded mammals, modern birds Animals developed migration techniques Quaternary Period = the past 2 million yrs Ice ages 1 st modern human fossils = 100,000 yrs old Cenozoic Era =“Recent”

Late Proterozoic Paleozoic Mesozoic Cenozoic Millions of years ago First skeletal elements First soft-bodied metazoans First animal traces First fishes First chordates Sudden diversification of metazoan families First vascular land plants First amphibians Jawed fishes diversify First reptiles Scale trees Seed ferns Major extinctions Reptiles diversify First mammals First dinosaurs First birds Dinosaurs diversify Extinction of dinosaurs First primates First flowering plants Mammals diversify Evolution of humans Quaternary Tertiary Cretaceous Jurassic Triassic Permain Pennsylvanian Devonian Mississippian Silurian Ordovician Cambrian Carbon- iferous era period events Geologic time scale, 650 million years ago to the present

Unit 9 Part 1: Virginia Provinces

Coastal Plain Description Essential Understanding: The Coastal Plain is a flat area composed of young, unconsolidated sediments underlain by older crystalline basement rocks. Geology These layers of sediment were produced by erosion of the Appalachian Mountains and Piedmont and then deposited on the Coastal Plain when sea levels were higher in the past.

Fall Line Description Essential Understanding: The edge of the Piedmont/Coastal Plain, where various rivers cross from hard bedrock to soft sediments, is marked by a line of rapids and waterfalls called the Fall Line. That physical pattern of rapids and waterfalls blocked ships from sailing further upstream, limiting water-based transportation of the European colonists. Geology Today, Interstate 95 is a rough guide to the location of the geologic boundary that separates the soft, sandy, light- colored sediments of the Coastal Plain from the hard bedrock of the Piedmont physiographic province.

Piedmont Description Essential Understanding: The Piedmont is an area of rolling hills underlain by mostly ancient igneous and metamorphic rocks. Geology The igneous rocks are the roots of volcanoes formed during an ancient episode of subduction that occurred before the formation of the Appalachian Mountains

Blue Ridge Description Essential Understanding: The Blue Ridge is a high ridge separating the Piedmont from the Valley and Ridge Province. Geology The billion-year-old igneous and metamorphic rocks of the Blue Ridge are the oldest in the state.

Valley and Ridge Description Essential Understandings: The Valley and Ridge province is an area with long parallel ridges and valleys underlain by ancient folded and faulted sedimentary rocks. Geology The folding and faulting of the sedimentary rocks occurred during a collision between Africa and North America. The collision, which occurred in the late Paleozoic era, produced the Appalachian Mountains.

Appalachian Plateau Description Essential Understandings: The Appalachian Plateau has rugged, irregular topography and is underlain by ancient, flat- lying sedimentary rocks. Extends into other states, like Kentucky and Tennessee. Only a small part of the Appalachian Plateau is in Virginia Geology The area is actually a series of plateaus separated by faults and erosional down-cut valleys. Most of Virginia’s coal resources are found in the plateau province.

Virginia Fossils In Virginia, fossils are found mainly in the Coastal Plain, Valley and Ridge, and Appalachian Plateau provinces. Most Virginia fossils are of marine organisms. This indicates that large areas of the state have been periodically covered by seawater. Chesapectan Jeffersonius (pictured below) is the Virginia State Fossil

Unit 9 Part 3: Virginia Resources coal Lime & lead Copper, iron, tin & turquoise Gold & pyrite Titanium bearing minerals

Coal in Appalachian Plateau Coal is an organic sedimentary rock used as a source of fuel Used in coal-fired power plants to generate electricity Major resource of Virginia

Resources By Region The Coastal Plain region… Important mineral resources found in the Coastal Plain include deposits of titanium bearing minerals. Oil and Natural Gas can also be found offshore. The Piedmont region… Important minerals are gold and pyrite. Some coal beds and methane are also found here. The Blue Ridge region… Copper, iron, tin and turquoise are mined from the Blue Ridge. Valley and Ridge region… Mineral resources include lime, lead, tin and iron. Oil, gas and coal are also found here. The Appalachian Plateau region… Coal beds can be found throughout. The coal is what makes this area economically important. There are some small oil fields.

Resources in Virginia Other resources of Virginia include: gravel and crushed stone for road construction silica for electronics zirconium and titanium for advanced metallurgy and limestone for making concrete.