Rock Record:
Layers of rock can contain a tremendous amount of evidence about
the characteristics/events that were in progress when those layers
were formed. They can be read be read like a detective novel.
Some key ideas that are useful in the study of the rock record:
-1) Principle of uniform process: the theory that the processes
acting on the earth today also acted on the earth in the past.
-2) Law of superposition: this is the idea that in a group
of rock layers, the top layer is generally the youngest and the
bottom layer is the oldest.
a. this seems to be obvious at first. However, crustal forces
can
bend rock layers to such a degree that the oldest rock is on
top and the youngest is on the bottom.
b. Layers of rock most often form when in a level position.
They must have been formed prior to the crustal force that
acted on them.
-3) Relative Age: a method of determining whether an object
is older or younger than another object. It does not determine
the
actual age of an object!
List 2 geologic examples here:
-4) Unconformity: a boundary separating younger rock layers from older layers that were exposed to erosion.
-Unconformities can yield information about relative age, possible
uplifting of the crust, when erosion began and ended, and when
deposition began.****
-They also yield clues about the history of a region-whether erosion
too place, whether it was underwater at one time.
List an example here:
Fossil Record:
Fossils: any naturally preserved part, trace, or entire remains
of a plant or animal that lived in the past.
List several examples here:
Fossils may be formed in the following manner:
1- preserved by freezing-
2- imbedded in tree sap (amber)
3- imbedded in tar
4- replacement of organic parts by minerals (petrification)
5- living material dissolved and left a mold
6- a cast, where the mold is filled in.
Fossils: may provide a variety of information or clues about
the organism.
1- size
2- locomotion
3- predator or prey adaptations
4- climatic or environmental conditions that were present at that
time
5- possible description/evidence on how conditions changed or
were changing.
Fossils have provided the following information:
a. existing conditions that were present at that time of that
organism lived.
b. how life changed
c. the kind of food that organisms.
Determining the age of rocks:
Key bed: a rock layer that is easily recognized and found in many
different places.
examples: dust/ash from a volcanic eruption
Index fossils: are useful in finding the age of a rock or rock
layer. They tend to be organisms that lived a short period of
time but were very abundant when alive.
example: trilobites
index fossils are very useful in measuring geologic time.
Radioactive Dating: This is a technique that uses the breakdown
rates of certain radioactive substances or elements to determine
the age of rocks.
radioactive- are element(s) that change into different elements
by losing material from the nucleus of its atoms.
Radioactive substances or elements have a steady decay rate- one that doesn’t vary. This steady decay rate or half-life- is the length of time taken for half of a given amount of a radioactive substance to completely change into another.
examples:
Uranium>>>>>>>>>Lead 4.5 billion years.
Potassium>>>>>>>>argon 135 million years
Carbon 14>>>>>>>>>Carbon 12 5800 years
Carbon 14 dating is the best method of for the determination of the age of young rocks.
Earth’s Calendar
Scientists divide the earth’s history into a series of time
periods called eras- which are time periods that are separated
by disturbances in the crust and changes in living things.
Era’s are sub-divided into Periods which in turn are divided into Epochs.
mya= millions of years ago
Phanerozoic Eon -----------------------------------Cenozoic Era-----------------------------------Quaternary
(1.8 mya to today)
(544 mya to present) -----------------------------(65 mya to today)
-------------------------------Holocene (11,000 years to today)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Pleistocene
(1.8 mya to 11,000yrs)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Tertiary
(65 to 1.8 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Pliocene
(5 to 1.8 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Miocene
(23 to 5 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Oligocene
(38 to 23 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Eocene
(54 to 38 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Paleocene
(65 to 54 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Mesozoic
Era >>>>>>>>>>>>>>>>>>>>Cretaceous
(146 to 65 mya)
(>>>>>>>>>>>>>>>>>>>>>>>>>>>>>245
to 65 mya) >>>>>>>>>>>>>>>>>>>Jurassic
(208 to 146 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Triassic
(245 to 208 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Paleozoic
Era >>>>>>>>>>>>>>>>>>>>Permian
(286 to 245 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>(544
to 245 mya) >>>>>>>>>>>>>Carboniferous
(360 to 286 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Pennsylvanian
(325 to 286 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Mississippian
(360 to 325 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Devonian
(410 to 360 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Silurian
(440 to 410 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Ordovician
(505 to 440 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Cambrian
(544 to 505 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Tommotian
(530 to 527 mya)
Precambrian Time >>>>>>>>>>>>>>>>>Proterozoic
Era >>>>>>>>>>>>>>Neoproterozoic
(900 to 544 mya)
(4,500 to 544 mya) >>>>>>>>>>>>>>>>(2500
to 544 mya) >>>>>>>>>>>>>>>>Vendian
(650 to 544 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Mesoproterozoic
(1600 to 900mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Paleoproterozoic
(2500 to 1600mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Archaean
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>(3800
to 2500 mya)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Hadean
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>(4500
to 3800 mya)