Relative Dating How do we determine a rocks age by the surrounding rocks? 1
Geologic History 2
Relative Dating Uniformitarianism - the idea that forces working on our planet today worked on our planet in the past in the same manner The present is the key to the past 3
Relative Dating Relative Dating - determination of the age of a rock or event in relation to the ages of other rocks or events 4
Relative Dating Principle of Superposition - basis for relative dating and the idea that the bottom layer is the oldest and each overlying layer gets progressively younger 5
Youngest Oldest Principle of Superposition 6
Relative Dating Original Horizontality - idea that sedimentary and igneous rocks are deposited in parallel layers to Earth s surface 7
Original Horizontality 8
Relative Dating Extrusions - molten rock flows onto the surface 9
Relative Dating Intrusions - when molten rock squeezes into preexisting rock layers Younger than the rocks that they crosscut Exception to the principle of superposition 10
Igneous Intrusions 11
Relative Dating Contact Metamorphism - temperature induced change of preexisting rocks along an intrusion 12
Relative Dating Faults - a crack in the bedrock where movement has occurred Younger than the rocks that they crosscut 13
Faults 14
Faults 15
Relative Dating Folds - when thrusting rock layers cause preexisting rock layers to overturn Exception to the principle of superposition 16
Folds 17
Relative Dating 18
Relative Dating Correlation - the process of showing that rocks or geologic events from different places are the same or similar age Correlation is the most effective method when using relative dating 19
Correlation 20
Relative Dating What to look for when correlating rocks: Similarities in Rocks Rock Sequence Mineral Composition Color Fossils 21
Relative Dating Fossils - remains or evidence of former living things Examples: bones, shells, footprints, and organic compounds (DNA) 22
Relative Dating Index Fossil - fossil used to define and identify geologic periods Best method for correlating rocks 23
Relative Dating Dinosaur Fossils 251-65 mya Trilobite Fossils 544-251 mya 24
Correlation 25
Relative Dating To be considered a good index fossil it needs to meet two criteria: 1. The organism existed over a large geographic area Large horizontal distribution 2. The organism existed over a short time Small vertical distribution 26
Relative Dating Geologic Time Markers - deposits spread over large areas that represent a specific date Examples: volcanic ash deposits and meteorite impacts 27
Relative Dating KT Boundary KT Asteroid - 65 mya Meteorite Impact 28
Relative Dating Krakatau - 1883 Volcanic Ash Deposit 29
KT Boundary 30
Absolute Dating How do we use radioactive decay in dating the absolute age of a rock, fossil, or event? 31
Absolute Dating Absolute Dating - using radioactive decay to determine the exact age of a rock, fossil, or event Radioactive Decay - the disintegration of an isotope over time 32
Step 1: Geologists drill for core samples. 33
Step 2: Geologists crush the samples into thin sections and a fine powder. 34
Step 3: Geologists analysis the samples for composition and inconsistencies. 35
Step 4: Geochronologists use spectroscopes to measure the ratio of stable to unstable products. 36
Periodic Table 37
Absolute Dating Isotopes - variations of an element that have the same atomic number but differing atomic masses Example: Stable carbon has a mass of 12 units called Carbon-12 Isotopic carbon has a mass of 14 units called Carbon-14 38
Absolute Dating Half-Life - the time required for half of a radioactive product to decay to a stable product In a given sample of a radioactive isotope half of the atoms will decay to a stable product, but the remaining half is still radioactive 39
Absolute Dating Each element has its own half-life that range from fractions of a second to billions of years 40
Absolute Dating The half-life of an isotope is not effected by any environmental factors such as temperature, pressure, or chemical reactions 41
Absolute Dating Uranium-238 - one of the most important isotopes when dating rocks or events millions of years ago Mass: 238 units Decay: Uranium-238! Lead-206 Half-Life: 4,500,000,000 years 42
Absolute Dating Carbon-14 - one of the most important isotopes when dating organic remains within tens of thousands of years Mass: 14 units Decay: Carbon-14! Nitrogen-14 Half-Life: 5,700 years 43
Age of the Earth 44
Early Evolution How did everything come to evolve on the Earth? 45
Early Evolution 4.6 Billion Years Ago Radioactive decay shows that Earth formed 46
Early Evolution 4.5 Billion Years Ago During the early formation Earth heated up due to radioactive decay of isotopes within the Earth s interior 47
Oldest Zircon Crystals - 4.4 billion years old Western Australia 48
Early Evolution 4.4 Billion Years Ago During early Earth s melting, materials separated into zones according to their densities Fe and Ni settled into the core Silicates formed the earliest crust Gaseous compounds made up the atmosphere 49
Early Evolution 4.2 Billion Years Ago Solid crust formed and plate tectonics started Gases trapped inside the Earth seeped out in a process called outgassing and created a completely different second atmosphere 50
Oldest Rocks - 4.28 billion years old Hudson Bay in Northern Quebec 51
Early Evolution 3.9 Billion Years Ago After the crust had cooled enough, water vapor in the atmosphere began to precipitate and form water on Earth 52
Early Evolution 3.8 Billion Years Ago Weathering, erosion, and deposition began and the first sedimentary rock was formed 53
The Potential for Life 54
Early Evolution 3.5 Billion Years Ago Life forms that used CO2 and released free oxygen began to evolve This allowed for oxygen to start collecting in our atmosphere 55
Early Evolution 3.5-2.8 Billion Years Ago Oxygen in the atmosphere reacted with iron in the soil to produce rust Resembled the surface color of current day Mars 56
Early Evolution 2.8 Billion Years Ago Most of the iron compounds that could have reacted with the oxygen had done so, thus oxygen in the atmosphere increased 57
Early Evolution 2.8 - Present Billion Years Ago Life slowly evolved from single-celled bacteria to multicellular to hard parts on life forms Single-Celled Multi-Celled 58 Shelled
Burgess Shale 59
Earth Science Reference Tables 60