What is an index fossil? a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found

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What is an index fossil? a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found.

Age of the Earth? 4.54 billion of years

Difference between a mold and cast? A cast is taken of a footprint. A mold is done of a bone or other part. One is the reverse of the other.  In a mold you are trying to make another copy of the bone.

What is an unconformity? An unconformity is a buried erosion surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continous.

What is a disconformity?  the surface of a division between parallel rockstrata, indicating interruption of sedimentaton.

What are the three Eras? The palaeozoic, The mesozoic, The Cenozoic.

The current periods?   The paleozoic era includes: The cambrian, The ordovician, The silurian, The Denovian, The carboniferous, and the permian, Mezosoic era includes: The triassic, The jurassic, and the Cretaceous. The Cenozoic era includes: The tertiary and the quarternary.

Law of superposition:

The law of superposition (or the principle of superposition) is a key axiom based on observations of natural history that is a foundational principle of sedimentary stratigraphy and so of other geology dependent natural sciences:

Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.

Law of original horizontality:  Sedimentary rocks are always deposited as horizontal, or nearly horizontal, strata, although these may be disturbed by later earth movements. The law was first proposed in the mid-17th century by Nicolaus Steno.

Law of cross cutting relationship:

the principle that a fault or body of rock is younger than any other body of rock that it cuts through.

Half life:

  • Relative age -  Relative means that we can determine  if something is younger than or older than something else.  Relative time does not tell how old something is, all we know is the sequence of events.  For example:  the sandstone in this area is older than the limestone. 

  • Absolute age-  Absolute age means that we can more or less precisely assign a number (in years, minutes, seconds, or some other units of time) to the amount of time that has passed.  Thus we can say how old something is.  For example:  The sandstone is 300 million years old. 

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