EARTH HISTORY UNIT TEST REVIEW April 21, 2016
Types of Fossils Trace fossil (TRACES of organisms) Mold fossil (cavity) Cast fossil (3D model) Petrified fossil (petrified wood) Carbonized fossil (imprint) Preserved fossil (complete organism)
Trace fossil Anything left behind by an organism. Footprints, tracks, burrows, droppings, etc. Would an egg fossil be a trace fossil? What can trace fossils tell us about organisms?
Cast fossil A three-dimensional model of an organism from deposited sediment. Fills in cavity left behind when organism decays. Example: trilobite fossil from class
Mold fossil A cavity in the shape of an organism, where no sediment has filled in. Forms similar to the clay mold we discussed in class. Could a cast fossil form from this? How?
Petrified fossil Minerals have replaced the organic materials within these samples. Example: petrified wood Features/texture of the original wood, but is actually rock
Carbonized fossil A carbon imprint of an organism or part of an organism when it was trapped between rock layers. Example: leaf imprint
Preserved fossil The entire organism is preserved within a substance (ice, amber, etc.) The only type of fossil we discuss where organic material is still present
Geologic Time Scale Organizes the major events on Earth with the appearance, evolution, and extinction of Earth s organisms. Uses the fossil record, which contains all known fossils and was used to organize the geologic time scale. Divided into eons, eras, periods, and epochs.
Index fossil Used to estimate the age of a rock layer using their position near an index fossil. Should be found in multiple regions within the same layer of rock.
Ice cores Help scientists learn about Earth s past climate, atmosphere, and geologic events. Contain particles trapped in snow and ice.
Dating fossils Radioactive dating: exact age in years using radioactive elements (such as carbon-14) Relative age: using superposition, simply says rock layers are older or younger.
Law of Superposition Youngest rocks are closest to the surface, oldest rocks are furthest from the surface. Determines relative age of sedimentary rocks.
Intrusions and Unconformities Intrusions are igneous rock formations that break through layers of sedimentary rock; they are younger than all layers they break through. Unconformities tell scientists how layers of rock have been eroded or tilted over Earth s past.
Example Which is the oldest rock layer? How old is layer P? What is the granite layer an example of? How old is the granite relative to the other layers?
Example How might you be able to reorder these rock layers? What can you infer about these rock layers? If you were to find a fossil in Layer P, what layer would you also expect to find it in? If you were to find a fossil in layer L, what layer would you also expect to find it in?
Example Which layer represents an unconformity? Which layer represents an intrusion? Which rock layer is the same age as the trilobite? Put the layers in order from youngest to oldest.
Types of Rocks Review Igneous rocks: form from magma or lava, tell us about the mantle layer Sedimentary rocks: form from deposited sediment, contain remains of organisms that tell us about Earth s past Metamorphic rocks: form from other rocks under heat and pressure.
Layers of Earth Review The Earth is divided into three layers: crust, mantle, and core. The core s heat is passed into the mantle, which creates convection. Convection is the circular motion of the mantle that also moves the crust.
Convergent boundaries Convergent boundaries are where two plates come together. Convergent boundaries destroy crust through subduction, where one plate is pushed under another and into the mantle layer. Convergent boundaries also form mountain ranges.
Divergent boundaries Divergent boundaries are where two plates spread apart or divide. Divergent boundaries form new crust through magma rising to the surface and cooling. Example: sea floor spreading
Transform boundaries Transform boundaries are where plates slide past one another. Can be horizontal (strike-slip) or vertical (dip-slip). Faults form at transform boundaries. Faults inform geologists how crust moves at transform boundaries.