same geologic processes shaping the earth today,have been working throughout earth's history.
"the present is the key to the past".
all geologic change happens suddenly.
today's geologist are in between.
determining whether something is older than other objects .
younger rocks lie above older rocks.
these rock layers can be disturbed.
ideal sequence of rock layers that contains all the known fossils and rock formations on earth from oldest to youngest.
features cutting through existing rock layers must be present.
break in the crust and layers slide.
molten rock from interior that squeezes into existing rock and cools.
layers bend and buckle from internal forces.
layers slanted, without folding.
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)
minerals fill in pore spaces of an organism's tissues.
organism's tissues completely replaced by minerals.
4 major ways to form fossils;
2.mummification(drying out fast)
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.
4.6 billion years on 12 hour clock
-last 3 eras discussed only take up about a day.
-humans are only found the last second.
-precambrian is all the way up until 11:00 pm.
-only the last hour represents the most recent eon.