fossils and the rock cycle. h ^ the rock cycle explains how one type of rock can be transformed into...
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Fossils and the Rock Fossils and the Rock CycleCycle
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The rock cycle explains how one type of rock can be transformed into another in nature.
The Geologic Cycle
3 key events: deposition, uplift, erosion
Deposition or SedimentationDeposition or Sedimentation
UpliftUplift
ErosionErosion
Erosion by waterErosion by water
Erosion by windErosion by wind
Geologic Cycle
Cycle repeats over and over through geologic time
Forms Strata: layers of rock
The rock cycle explains how one type of rock can be transformed into another in nature.
Index Fossils
Use fossil layers to date rocks: index fossils
FossilsFossils
What is a Fossil?
Any evidence of past life, including remains, traces, imprints as well as life history artifacts. Examples of artifacts
include fossilized bird's nests, bee hives, etc.
Mastodon at Wheaton CollegeMastodon at Wheaton College
How Fossils are Formed
About 67 million years ago -- A Tyrannosaurus rex died and its body was quickly covered by riverbed sand and mud.
Over time, pressure and some remineralization turned its bones to fossils.
The Fossil RecordThe Fossil Record
• All of the fossils that All of the fossils that have existed have existed throughout life’s throughout life’s history, whether they history, whether they have been found or have been found or not.not.
Tully MonsterTully Monster; IL State Fossil; IL State Fossil
Fossils
Usually found in sedimentary rock Sometimes in metamorphic rock
These are often distorted, hard to interpret
Upper layers - younger Deeper layers – older
Principle of Fossil Succession
There is a unique, non-repeating pattern (history) of fossils through stratigraphic time.
All rocks containing fossils of the same species were deposited during the duration of that species on Earth.
Correlation by fossils. Certain index fossils are keys . Certain index fossils are keys to matching sedimentary strata in widely separated to matching sedimentary strata in widely separated outcrops outcrops
Used in conjunction with radioisotope techniques to age rock layers
Unconformities Unconformity: contact between layers of rock
that should not touch; represents a gap in the fossil/geological record
Layers of sandstone over pink granite
Hutton's unconformity at Siccar Point Berwickshire, Scotland Hutton's unconformity at Siccar Point Berwickshire, Scotland This was the very first (1789) example of an unconformityThis was the very first (1789) example of an unconformity
Hutton's Hutton's unconformityunconformity
Ordovician/Silurian unconformity in New York stateOrdovician/Silurian unconformity in New York state
Precambrian/Cambrian unconformity near St. Louis – 1 billion years is missingPrecambrian/Cambrian unconformity near St. Louis – 1 billion years is missing
Unconformities
Disconformity: gap in geological record Caused by long period
of erosion between episodes of sedimentation
Or by faulting and uplift Fossils in the two layers
may be very different
Unconformity of Cambrian sandstone on Precambrian gneiss. North of Kingston, Ontario, Canada.
Unconformities
Disconformity: missing strata between layers that are parallel to each other. Often difficult to detect in the field. Must use fossils or other correlation methods. Angular unconformity: younger strata overlie an erosion
surface on tilted or folded rocks. Implies a specific sequence of events.
Nonconformity: contact with overlying sedimentary rocks on top of an erosion surface of plutonic or metamorphic rocks. Implies long-lived erosion prior to burial and re-deposition.
Angular Unconformity
Nonconformity
Angular
Nonconformity
Angular Unconformity
Nonconformity
Great Lakes Lost Interval
Mesozoic EraVery recent glacial sediments above ancient
bedrock
Due to long period of erosion of uplifted sediments
Big gap in fossil record