Geologic time. Goal to understand how we determine relative and numerical ages of geologic events.
Geologic Time We know its BIG…but HOW do we know that?
-
Upload
khalil-perdue -
Category
Documents
-
view
221 -
download
1
Transcript of Geologic Time We know its BIG…but HOW do we know that?
Geologic TimeWe know it’s BIG…but HOW do we know that?
BIG QUESTIONS:
1) What methods do we use to figure out the age of our earth?
2) How do fossils help
us to learn things about the past?
UniformitarianismUniformitarianism is the assumption that the same
processes that operate on the earth now have always operated on the earth in the past.
For example: Given a long period of time, a river can erode a valley. Based
on the principle of uniformitarianism, all valleys in the past have been formed by
rivers eroding them and all future valleys will be formed
this same way
Relative Dating
Relative dating refers to the relative order in which things occurred, without knowing the actual date of
each event.
Relative dating relies on several principles.
Principle of Original HorizontalityThis principle states that layers of sediment are
originally deposited horizontally under the action of gravity.
This means that any “sloping” of layers
must have occurred AFTER the layers
formed
Principle of SuperpositionLayers of earth are deposited in a time sequence, with the oldest on the bottom and the youngest on the top.
Cross-Cutting Relationships
The principle of cross-cutting relationships states that the geologic feature which cuts another is the younger of the two features.
Younger
InclusionsThis principle states that fragments included in a
host rock are older than the host rock itself.
This rock (inclusion) must have existed BEFORE the lava (host rock) formed…
therefore it is older.
Practice…Identify the layers from oldest to youngest
Absolute Dating
Absolute dating refers to the exact age in years of an object
Several methods exist for absolute dating.
Radiometric Dating
Technique used to date materials such as rocks,
using radioactive materials contained in the
rocks/fossils
This exact age can then help us with some aspects
of relative dating
FossilsThe preserved remains or traces of animals, plants, and
other organisms from the past
Many fossils can be dated using relative AND absolute dating
Index Fossils
A particular plant/animal that only existed for a very short period of time on the earth
Useful for relative dating purposes.