Geology Geologic Time

Geology The study of the EARTH, rocks, and fossils.

Uniformitarianism The idea that the earth has been shaped by gradual changes (erosion, deposition) throughout history. These changes are still occurring. James Hutton proposed this idea and wrote Theory of the Earth. The present is the key to the past. What’s going on now is what went on long ago. Long Ago Now

Catastrophism Changes in the Earth happen suddenly through events called catastrophes!!

Law of Superposition Geologic Column Youngest rocks In horizontal rock layers, the oldest layer is at the bottom. Scientist use this to relatively date the sedimentary rock layers. Oldest rocks

Why is igneous rock always younger than any rock it cuts through? In order for the igneous rock to cut through rock layers, the rock layers around it must have existed before the molten rock could cut through it. https://www.youtube.com/watch?v=A5LdZJiKsVk

Extrusion vs. Intrusion Extrusion is an igneous rock layer formed when lava flows onto Earth’s surface and hardens. Intrusion is an igneous rock layer formed when magma hardens beneath the Earth’s surface. Also example of unconformity Intrusions

Unconformity https://www.youtube.com/watch?v=rS4lnPYUYkg A break or gap in the geologic record that may indicate episodes of crustal deformation, erosion, and sea level variation Intrusions

Types of Unconformities Disconformity-missing layer of rock in a sequence of parallel rock layers Angular unconformity-missing layer that exists between horizontal and folded rock layers

Fault A break in a body of rock along which one block slides against the other

Index Fossil Fossils of organisms that were common that lived in many areas and that existed only during specific spans of time. This kind of fossil is important for figuring out when rock layers were formed.

Relative Dating I’m older than all of them! I’m the youngest! Using index fossils to compare the age of rocks works the same way! I’m older than the baby, but younger than the man.

Absolute Dating finding the exact date of rock or fossil using scientific processes Radiometric Dating is one way to do this. Finding the half-life of a substance means finding out how long it takes ½ of the radioactive isotopes (parent) to change to become stable (daughter). Parent ½ change = Half life Daughter

Fossils Fossils- traces or remains of living things from long ago. Many forms such as shells, bones, and teeth. What allows this to happen? The minerals replace the remains forming a fossil.

Original Remains Fossils that are the actual bodies or body parts of organisms are called original remains. They give direct evidence of forms of life that lived long ago Ice, amber, and tar have provided scientist this type of evidence

Fossil Formation Conditions have to be just right for a fossil to form in rock Must be preserved before decomposition Rock fossils mainly only have the hard remains not the soft remains because the soft parts decompose to quickly. Form in sedimentary rock like sand or mud. Igneous rock (describes rock formed under conditions of intense heat or produced by the solidification of volcanic magma on or below the Earth's surface) never contain fossils because the heat from which the rock came from would have destroyed any fossil remains.

Not original remains impressions or traces Molds and Casts – organism dies and falls into soft sediment over time the sediment becomes rock and the organism decays, leaving a mold. Petrified Wood- stone fossil of a tree. Water passes through the cells of the tree depositing minerals which take the place of the cells producing a stone likeness. Carbon Films- visible carbon left behind by an organism these can show soft parts in organisms. Trace Fossils- preserved footprints, trails, animal holes , and feces these fossils allow scientist to infer about what animals ate how fast did they travel.

Ice Cores and Tree Rings https://www. youtube. com/watch Ice Cores- Tubular sample of ice shows layers of snow and ice built up over time. Scientists analyze air trapped in the ice to learn how the atmosphere has changed. Differences in air content at different levels shows how much temperature went up and down over long periods of time. Tree Rings Width varies Dry years- thin rings Wet years- thick rings Helps to determine weather patterns from the past.

Eon Era Period Epoch Geologic time scale Divides Earth’s history into intervals of time defined by major events or changes on Earth. Eon Era Period Epoch

Division of Time Eon – Earth’s history is divided into four eons. Hadean , Archean, Proterozoic , Phanerozic (Current) Era – Paleozoic , Mesozoic, and Cenozoic era are division of the Phanerozic eon. Periods- era are divided into periods Epoch- periods of the Cenozoic are divided into epochs.

The Specifics: Haden , Archean, and Proterozoic eons are called Precambrian (consists mostly of tiny fossils that cannot be seen without a microscope.) Phanerozoic eon stretches from Precambrain time to present. Why is it divided into smaller units of time? Paleozoic “ancient life” Mesozoic “middle life” and “age of reptiles” Cenozoic “recent life” The time reflects many changes or extinctions in life forms on Earth.

Important Events in Earth’s Past First Mammals appear in the Triassic Period of the Mesozoic era. Dinosaurs lived and became extinct during the Mesozoic era. First humans appear in the Cenozoic era Create your personal time line lab activity.

extinction They all died out!