Two Conceptions of Earth History: Catastrophism Assumption: Great Effects Require Great Causes Earth History Dominated by Violent Events Uniformitarianism Assumption: We Can Use Cause And Effect to Determine Causes of Past Events Finding: Earth History Dominated by Small-scale Events Typical of the Present. Catastrophes Do Happen But Are Uncommon
Uniformitarianism Continuity of Cause and Effect Apply Cause and Effect to Future - Prediction Apply Cause and Effect to Present - Technology Apply Cause and Effect to Past Uniformitarianism The Present is the Key to the Past Coined by James Hutton - Father of modern geology
Ripple Marks, Bay Beach
Fossil Ripple Marks, Baraboo Range
Modern Mud Cracks
Fossil Mud Cracks, Virginia
Two Kinds of Ages Relative - Know Order of Events But Not Dates Civil War Happened Before W.W.II Bedrock in Wisconsin Formed Before The Glaciers Came Absolute - Know Dates Civil War 1861-1865 World War II 1939-1945 Glaciers Left Wisconsin About 11,000 Years Ago
Principles associated with Relative Dating The comparing of rock units to decipher their age relative to one another Principle of Superposition Rock layer above is younger than the ones below it. (Oldest on bottom, youngest on top) May not apply to rocks that have been folded (can get turned upside-down). Principle of Crosscutting Relationships Any feature (e.g. fault or intrusion) that cuts across rocks is younger than the youngest rock that is cut.
Unconformities Unconformities are surfaces in rock that represent periods of erosion or nondeposition. In other words, time has been left out of the physical geologic rock record.
Relative dating estimates the time during which an organism lived. It compares the placement of fossils in layers of rock. Scientists infer the order in which species existed. Absolute Dating can give the exact age Uses Radiometric Age Dating
Radiometric dating uses decay of unstable isotopes. Isotopes are atoms of an element that differ in their number of neutrons. neutrons protrons
Radiometric dating uses decay of unstable isotopes. Isotopes are atoms of an element that differ in their number of neutrons. A half-life is the amount of time it takes for half of the isotope to decay.
Absolute Age Dating If we know how much of the original (Parent) material is left then we can determine how many half lives the rock has been through. If you know how long a half life lasts (half rate) for a particular isotope then you can multiply the half rate by the number of half lives the rock has been through and you get the age.
Index fossils are another tool to determine the age of rock layers. Index fossils can provide the relative age of a rock layer. existed only during specific spans of time occurred in large geographic areas Index fossils include fusulinids and trilobites.
KEY CONCEPT Specific environmental conditions are necessary in order for fossils to form.
Fossils can form in several ways. Permineralization occurs when minerals carried by water are deposited around a hard structure.
A natural cast forms when flowing water removes all of the original tissue, leaving an impression.
Trace fossils record the activity of an organism.
Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.
Preserved remains form when an entire organism becomes encased in material such as ice.
Specific conditions are needed for fossilization. Only a tiny percentage of living things became fossils.
KEY CONCEPT The geologic time scale divides Earth s history based on major past events.
The geologic time scale organizes Earth s history. The history of Earth is represented in the geologic time scale. 100 250 550 1000 2000 PRECAMBRIAN TIME This time span makes up the vast majority of Earth s history. It includes the oldest known rocks and fossils, the origin of eukaryotes, and the oldest animal fossils. Cyanobacteria
Most recent Ice Age Humans arrive Major Mass Extinction Age of Dinosaurs Major Mass Extinction Age of Coal Formation Age of Fishes The Geologic Time Scale Origin of the Earth 4.55 Billion years First multicelled organisms
Eras last tens to hundreds of millions of years. consist of two or more periods three eras: Cenozoic, Mesozoic, Paleozoic
Periods last tens of millions of years. most commonly used units of time on time scale associated with rock systems. Epochs last several million years.
Pre Cambrian From beginning (4.6 billion years ago) to 545 million years ago (mya) Makes up 90% of Earth s history
Highlights 4.6 bya Earth forms 4.3 bya Moon forms 3.5 bya first life on Earth 2.5 bya Stabilizing oxygen in atmosphere
Pre Cambrian many rocks eroded significantly first life form was cyanobacteria (3.5 bya)
Cyanobacteria Cyanobacteria (blue green algae) added large amounts of oxygen (through photosynthesis) to the atmosphere... made it possible for animals to evolve
Where did the first cell come from?
STANLEY MILLER AND HAROLD UREY EXPERIMENT
Mass extinctions mark the beginning and end of eras!
PALEOZOIC ERA The Age of Invertebrates From 545 mya to 245 mya warm, shallow seas 544 mya first fossils with hard parts
Firsts : land plants, fish, amphibians, reptiles and insects (400 mya) Appalachians form divided into seven periods
North America was at the equator; climate was very hot and humid Pennsylvania was underwater
Earth During the Silurian (430+ million years ago)
Earth during: Devonian ~410 million years ago Mississippian ~330 million years ago Permian ~250 million years ago
Most of the limestone and coal found in Pennsylvania formed during the Paleozoic Era (300 mya)
Paleozoic * Pangaea breaks up 250 mya
Cambrian Explosion Marine life forms: trilobites - relative of horseshoe crab brachiopods - look like clams crinoids - relative of starfish and sea urchins
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale trilobite brachiopod crinoid
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale THE MESOZOIC ERA ( Age of Reptiles ) From 245 mya to 66 mya Firsts : mammals, birds and angiosperms (flowering plants) 200 mya
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale Dinosaurs evolve and later become extinct Pangaea breaks up Rocky Mountains form
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale Divided into three periods: - Triassic - Jurassic dinosaurs flourish - Cretaceous dinosaurs become extinct (65 mya)
What Killed the Dinosaurs?
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale The extinction of dinosaurs marks the end of the Mesozoic Era and the beginning of
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale CENOZOIC ERA Age of Mammals From 66 mya to present Most complete geologic record Mammals and flowering plants abundant (60 mya)
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale Alps and Himalayas form Grand Canyon Forms Homo sapiens (humans) evolve (500,000 yrs ago)
The 13.1 Fossil Ecologists Record Study and Relationships Geologic Time Scale Divided into 2 periods and each period is further divided into epochs We are living in the Recent Epoch of the Quaternary Period of the Cenozoic Era
1 mya beginning of human history 18,000 years ago was the peak of the last glaciation
What s Next The hot topic today is what will happen next: What will life be like on planet Earth? Will there be a new dominant species? How/when will be the next mass extinction to end the age of mammals? A couple of theories:
Population Growth
Global Warming
2012
Chuck Norris