index fossils and geologic time “the past is the key to the present”
TRANSCRIPT
Index Fossils and Geologic Time“The Past is the Key to the
Present”“The Past is the Key to the
Present”
Determining Relative AgeDetermining Relative Age
Rock layers (strata) detail sequences of Earth’s events the oldest rock layers
are on the bottom and youngest are on top
Relative Age (Approximate)
Fossils
Rock layers (strata) detail sequences of Earth’s events the oldest rock layers
are on the bottom and youngest are on top
Relative Age (Approximate)
Fossils
DeterminingAbsolute AgeDeterminingAbsolute Age
Absolute Age = Exact Age Radioactive Decay Half-Life Carbon Dating
Fossils
Absolute Age = Exact Age Radioactive Decay Half-Life Carbon Dating
Fossils
The Fossil RecordThe Fossil Record
Remains or traces of animals or plants from a previous geologic time
Quick burial; Sedimentary Rock
Used for absolute and relative ages Fossil succession
(fossils succeed one another in a definite order)
Remains or traces of animals or plants from a previous geologic time
Quick burial; Sedimentary Rock
Used for absolute and relative ages Fossil succession
(fossils succeed one another in a definite order)
Kinds of Fossils Hard Parts Trace (footprint) Imprints, molds and
casts Coprolites (dino doo-
doo) Gastroliths (Digestive
stones)
Kinds of Fossils Hard Parts Trace (footprint) Imprints, molds and
casts Coprolites (dino doo-
doo) Gastroliths (Digestive
stones)
Index FossilsIndex Fossils
Fossils found exclusively in rock layers of a particular geologic age Present over a wide
area Easily distinguished Relatively short
geologic time span Large numbers within
rock layers
Fossils found exclusively in rock layers of a particular geologic age Present over a wide
area Easily distinguished Relatively short
geologic time span Large numbers within
rock layers
More on Index FossilsMore on Index Fossils
Used to establish the relative ages of the rock layers in which the fossils are found (trilobite)
Used to date rock layers found in widely separated areas
Used to locate oil and natural gas deposits
Used to establish the relative ages of the rock layers in which the fossils are found (trilobite)
Used to date rock layers found in widely separated areas
Used to locate oil and natural gas deposits
Geologic TimeGeologic Time
Fossil record (worldwide) used to construct a “geologic column” which shows the ordered arrangement of rock layers based upon ages Distinguished primarily by kinds of fossils
they contain Fossils in the lower, older layers are very
different than those within the younger layers
Fossil record (worldwide) used to construct a “geologic column” which shows the ordered arrangement of rock layers based upon ages Distinguished primarily by kinds of fossils
they contain Fossils in the lower, older layers are very
different than those within the younger layers
Divisions of Geologic TimeDivisions of Geologic Time
Earth’s geologic history is punctuated by major changes in the earth’s surface or climate and by the extinction of various species
Geologists use these events as the basis for dividing the geologic time scale (Eons) into smaller units
Eras Periods Epochs
Earth’s geologic history is punctuated by major changes in the earth’s surface or climate and by the extinction of various species
Geologists use these events as the basis for dividing the geologic time scale (Eons) into smaller units
Eras Periods Epochs
Precambrian TimePrecambrian Time
4.6 bya to 570 mya 88% of Earth’s
history Atmosphere forms Fossils rare
Soft-bodied Deformed rock
Bacterial reefs Worms, jellyfish and
one-celled organisms in late precambrian
4.6 bya to 570 mya 88% of Earth’s
history Atmosphere forms Fossils rare
Soft-bodied Deformed rock
Bacterial reefs Worms, jellyfish and
one-celled organisms in late precambrian
Paleozoic EraPaleozoic Era
570 mya to 245 mya
Dramatic increase in plant and animal species Rich marine and
land fossil record
570 mya to 245 mya
Dramatic increase in plant and animal species Rich marine and
land fossil record
More on the Paleozoic EraMore on the Paleozoic Era
First vertebrates (fishes) appear First land plants and animals appear First amphibians appear First reptiles appear Pangaea comes together Mass extinctions mark the end of this
era Marine invertebrates (trilobites, eurypterids)
due to retreat of the seas
First vertebrates (fishes) appear First land plants and animals appear First amphibians appear First reptiles appear Pangaea comes together Mass extinctions mark the end of this
era Marine invertebrates (trilobites, eurypterids)
due to retreat of the seas
Mesozoic EraMesozoic Era
245 mya to 65 mya Surface of the earth
changed dramatically (break-up of Pangaea)
Conditions favored the survival of the reptiles
245 mya to 65 mya Surface of the earth
changed dramatically (break-up of Pangaea)
Conditions favored the survival of the reptiles
More on the Mesozoic EraMore on the Mesozoic Era
Dinosaurs first appear First mammals appear Flying reptiles and first birds appear First flowering plants appear Mass extinctions (dinosaurs, marine
animals) mark the end of this era Cretaceous-Tertiary Boundary (K-T) Meteorite-Impact hypothesis
Dinosaurs first appear First mammals appear Flying reptiles and first birds appear First flowering plants appear Mass extinctions (dinosaurs, marine
animals) mark the end of this era Cretaceous-Tertiary Boundary (K-T) Meteorite-Impact hypothesis
Cenozoic EraCenozoic Era
65 mya to present Time of increased
tectonic activity Dramatic changes
in climate (ice ages)
65 mya to present Time of increased
tectonic activity Dramatic changes
in climate (ice ages)
More on the Cenozoic EraMore on the Cenozoic Era
“Age of Mammals” Divided into two periods:
Tertiary: time before the last major ice age Whales, Horses, deer, grazing herds,
wolves, raccoons Quaternary: Last ice age (Pleistocene)
to present Wooly mammoths, rhinos, humans
“Age of Mammals” Divided into two periods:
Tertiary: time before the last major ice age Whales, Horses, deer, grazing herds,
wolves, raccoons Quaternary: Last ice age (Pleistocene)
to present Wooly mammoths, rhinos, humans