same geologic processes shaping the earth today,have been working throughout earth's history.
"the present is the key to the past".
ideal sequence of rock layers that contains all the known fossils and rock formations on earth from oldest to youngest.
missin part of the geologic column.
-must question if present or removed
-3 kinds:1.discomformity:parallel rock layer missing;uncomformity is common.
2.noncomformity:sedim. layers lie on top of eroded ign.or meta.
3.angular uncomformity.happens between horizontal rock layers and tillted or folded layers.
establish the age by determining the # of years it has existed.
3 methods:U-PB(4.5 by)
kinds of fossils
1.trace:any naturally preserved evidence of an animal's activity .Ex .track,burrow,coprolite.
2.mold/cast:cavity in ground or rock where a plant/animal was buried .
3.index;fossils of organisms that lived during a short well-defined period of time (able to provide a specific date).
geologic time scale
a scale that divides earth's 4.6 billion year history into intervals.
divisions of time :
eons_ eras_ periods_ epochs.
different intervals are formed because of major changes on earth:
1.appearance of lifeforms.
2.change in global climate.
3.change in rock types.
-age of amphibians.
-no land organisms at start.
-by the end amphibians were taking over and insects were abundant.
-came to an end with a mass extinction .nearly 90% of all species died.(largest one on record).
-age of reptile.
-means middle life in greek or latin.
-birds and small mammals begin to be seen towards the end.
-ended with 50% mass extinction of all epecies on earth.
-age of mammals.
-means recent life in greek or latin.
-65 MYA to current.
-mammals became abundant.