# Relative Time.

## Presentation on theme: "Relative Time."— Presentation transcript:

Relative Time

Relative Dating Relative dating – events are placed in a sequence, but actual occurance dates are unknown. Who is older, Mr. Kopp or Justin Bieber? What are our actual ages? – Absolute Dating

Relative Dating Geologic Laws
Principle of Uniformitarianism – idea that the same geologic processes that are occuring today ALSO occurred in the past

Law of Original Horizontality
SEDIMENT IS DEPOSITED HORIZONTALLY

Law of Superposition If sedimentary rocks are undisturbed – THE OLDEST LAYERS ARE ON THE BOTTOM and YOUNGER LAYERS ARE ON TOP youngest C D B oldest A

Law of Crosscutting A cutting feature is younger than the layers it cuts through youngest B C E D A oldest

Law of Included Fragments
Pieces of rocks are older than the layers of rock in which they are found D youngest C A e e e B oldest

“Unconformity Rule” A place in the rock record where layers of rock are missing and gaps in geologic time exist. The layers were deposited and worn away OR never existed. The result is a large difference between rocks above and below the eroded surfaces. B C E D A

Law of Faunal Succession
Older rocks contain the remains of older and more simple creatures and younger rocks contain younger more complex creatures

Absolute Time

Radiometric Dating Calculation of the exact age of rocks using radioactive isotopes Remember Relative Dating is only a comparison of the ages of rock layers (older or younger)

Atomic # = ? Atomic Mass # = ? Isotope – an element with the same number of protons but a DIFFERENT NUMBER OF NEUTRONS = unstable nucleus Radioactivity: when nuclei are unstable (radioactive isotopes), they spontaneously break apart or decay

How Does Absolute Dating Work?
PARENT = radioactive isotope which decays into a stable DAUGHTER product. Radioactive decay continues until a stable daughter product is formed….which happens within a predictable time period known as a half-life.

How does Relative Dating Work?
Half-life – rate of radioactive decay (the amount of time it takes for HALF of the nuclei of a radioactive isotope to decay into its stable daughter product) Uranium-238 decays into Lead-206 (4.5 by) Uranium-235 decays into Lead-207 (713 my) Thorium-232 decays into Lead-208 (14.1 by) Rubidium-87 decays into Strontium-87 (47 by) Potassium-40 decays into Argon-40 (1.3 by)

How does absolute dating work?
Each radioactive isotope has been decaying at a constant rate since the formation of the rocks in which it occurs. Question? Why have the oldest rocks on Earth been dated at 3.9 billion years old yet the Earth has been determined to be 4.6 billion years old?

Carbon-14 Radiocarbon dating – all organisms contain carbon-14 allowing scientists to determine the age of recent fossils Carbon -14 has a half life of 5,730 and can help scientists date recent geologic events up to 75,000 years ago making it extremely valuable for human history

Index Fossils Used to define and identify geologic periods
Widespread, existed in a specific period of time

(Divided based upon major geologic and evolutionary events)
Geologic Time Scale (Divided based upon major geologic and evolutionary events)

Eons Largest divisions of geologic time
1) Pre-Cambrian 4.6 billion – 540 million years ago Largest period of time 7/8 of the Earth’s History Formation of the Earth, rise of life (3.7 bya), to the first invertebrates 2) Phanerozoic (540 million years ago to present day) - Complex life on Earth

Eras 2nd Largest divisions of geologic time
1) Pre-Cambrian – rise of early life 2) Paleozoic – rise of complex life 3) Mesozoic – age of the dinosaurs 4) Cenozoic – age of mammals

Periods and Epochs Pre-Cambrian 4.6 billion years ago to 540 million years ago (life appears 3.7 bya) Earth Formed, Moon Formed, Heavy Bombardment Bacteria Stromatolites (blue-green algae)

Periods and Epochs Phanerozoic Eon, Paleozoic Era
Cambrian Period 540 to 490 mya Most major animal groups appear Arthropods and mullosks

Periods and Epochs Phanerozoic Eon - Paleozoic Era
Ordovician Period – 490 to 443 mya Massive Marine Life Diversification

Periods and Epochs Phanerozoic Eon, Paleozoic Era
Silurian Period – 443 to 417 million years ago Life comes on land

Periods and Epochs Phanerozoic Eon, Paleozoic Era
Devonian Period – 417 to 354 million years ago Age of fishes

Periods and Epochs Phanerozoic Eon, Paleozoic Era Carboniferous Period
Mississippian and Pennsylvanian Epoch – 354 to 290 million years ago Age of plants

Periods and Epochs Phanerozoic Eon Paleozoic Era
Permian Period – 290 to 248 million years ago MASS EXTINCTION of 90% of species

Periods and Epochs Phanerozoic Eon, Mesozoic Era
Triassic Period – 248 to 206 million years ago Rise of reptiles

Periods and Epochs Phanerozoic Eon, Mesozoic Era
Jurassic Period – 206 to 144 million years ago Dinosaurs rules the land

Periods and Epochs Phanerozoic Eon, Mesozoic Era
Cretaceous Period – 144 to 65 million years ago Rise of Flowering plants – End of Dinosaurs

Periods and Epochs Phanerozoic Eon, Cenozoic Era Tertiary Period
Paleocene Epoch - 65 to 54.8 million years ago Age of Mammals

Periods and Epochs Phanerozoic Eon Cenozoic Era Quarternary Period
Pleistocene Epoch to million years ago to 10,000 years ago Modern organisms – RISE OF HUMANS

Periods and Epochs Phanerozoic Eon Cenozoic Era Quarternary Period
Holocene Epoch - 10,000 years ago to present