Transcript A View of Earth`s Past

A View of Earth’s Past
Chapter 8 & 9
• law of superposition the law that a
sedimentary rock layer is older than the
layers above it and younger than the
layers below it if the layers are not
disturbed
relative age - the age of an object in
relation to the ages of other objects
Law of Superposition
• Ripple marks - are small waves that form
on the surface of sand because of the
action of water or wind.
– When the sand becomes sandstone, the
ripple marks may be preserved.
unconformity a break in the geologic
record created when rock layers are
eroded or when sediment is not deposited
for a long period of time
• fault - a break or crack in Earth’s crust
along which rocks shift their position
• intrusion - a mass of igneous rock that
forms when magma is injected into rock.
radiometric dating a method of determining the
absolutes age of an object by comparing the
relative percentages of a radioactive (parent)
isotope and a stable (daughter) isotope.
half-life - time required for half of a sample of a
radioactive isotope to break down by
radioactive decay to form a daughter isotope.
• Organic remains, such as wood, bones, and
shells that are less than 70,000 years old can
be determined by using a method known as
carbon-14 dating, or radiocarbon dating.
fossils - the trace or remains of an organism
that lived long ago, most commonly
preserved in sedimentary rock
paleontology - the scientific study of fossils
Fossilization methods
• amber - hardened tree sap
• Tar seeps
• Freezing
• Mummification
• Petrification
• Types of fossils:
– Trace fossils
– Imprints
– Molds & Casts
– Coprolites
– Gastroliths
– Index fossils
Geologic map of bedrock of Ohio
• geologic column an ordered
arrangement of rock layers that is based
on the relative ages of the rocks and in
which the oldest rocks are at the bottom
Where would you find fossils of extinct
animals on a geologic column?
Scientists use geologic columns to estimate
the age of rock layers that cannot be dated
radiometrically
• The geologic
history of Earth is
marked by major
changes in Earth’s
surface, climate,
and types of
organisms.
• EonEraPeriodEpochOld PeriodsPhanerozoic
Eon
543 mya to PresentCenozoic Era
65 mya to Present NeogeneHoloceneQuaternary 1.8 mya to
PresentPleistocenePlioceneTertiary 65 to 1.8
myaMiocenePaleogeneOligoceneEocenePaleoceneMesozoic Era
248 mya to 65 myaCretaceous 144 mya to 65 myaJurassic 206 to
144 myaTriassic 248 to 206 myaPaleozoic Era
543 to 248 myaPermian 290 to 248 myaCarboniferous 354 to 290
myaDevonian 417 to 354 myaSilurian 443 to 417
myaOrdovician 490 to 443 myaCambrian 543 to 490
myaPrecambrian Time
4,500 to 543 myaProterozoic Era 2,500 to 543 myaArchaean 3,800
to 2,500 myaHadean 4,500 to 3,800 mya
• eon - largest unit of geologic unit of time
• 4 Eras of Geologic time:
– Hadean eon
– Archean eon
– Proterozoic eon
– Phanerozoic eon
era - unit of geologic time that includes two
or more periods
• Paleozoic rocks contain fossils of a wide
variety of marine and terrestrial life forms.
• After the Paleozoic Era the Mesozoic Era
began and lasted about 183 million years.
• Mesozoic fossils include early forms of
birds and reptiles.
• The present era is the Cenozoic Era,
which began 65 million years ago. Fossils
of mammals are common in Cenozoic
period - a unit of geologic time that is longer
than an epoch but shorter than an era
Epoch - a subdivision of geologic time that
is longer than an age but shorter than a
period.
evolution - an inheritable change in the
characteristics within a population from
one generation to the next; the
development of new types of organisms
from preexisting types of organisms over
time
Evolution
Precambrian time the interval of time in
the geologic time scale from Earth’s
formation to the beginning of the
Paleozoic era, from 4.6 billion to 542
million years ago.
• stromatolites - one of the few Precambrian
fossils that have been discovered are.
– The presence of stromatolite fossils in Precambrian
rocks indicates that shallow seas covered much of
Earth during that time.
Paleozoic Era - the geologic era that followed
Precambrian time and that lasted from 542
million to 251 million years ago.
– Paleozoic rocks hold an abundant fossil record. The
number of plant and animal species on Earth
increased dramatically at the beginning of the
Paleozoic Era.
– Because of this rich fossil record, the Paleozoic Era
has been divided into seven periods.
• The Cambrian Period is the first period of
the Paleozoic Era.
– Marine invertebrates thrived in the warm
waters that existed during this time.
– The most common of the Cambrian
invertebrates were trilobites.
– The second most common animals of the
Cambrian Period were the brachiopods, a
group of shelled animals.
The Ordovician Period
• clamlike brachiopods and cephalopod mollusks
became the dominant invertebrate life-form.
• first vertebrates appeared.
The Silurian Period
• During the Silurian Period, echinoderms, relatives of
modern sea stars, and corals became more common.
• Near the end of this period, the earliest land plants as
well as animals evolved
The Devonian Period - the Age of Fishes
– fossils of many bony fishes were discovered in
rocks of this period.
– lungfish, had the ability to breathe air. Another type
of fish, Rhipidistians, were air-breathing fish that
had strong fins that may have allowed them to crawl
onto the land for short periods of time.
– Land plants, such as giant horsetails, ferns, and
cone-bearing plants also began to develop during
The Carboniferous Period
• In North America, the Carbiniferous Period
is divided into the Mississippian and
Pennsylvanian Periods.
• the climate was warm, forests and
swamps covered most of the world.
• Amphibians and fish continued to flourish,
and the first vertebrates that were adapted
to live on land appeared.
The Permian Period - marks the end of the
Paleozoic Era,
– a mass extinction of several life-forms occurred at
the end of this period.
– the continents had joined to form Pangaea
mass extinction - large numbers of species
become extinct
Mesozoic Era the geologic era that lasted from
251 million to 65.5 million years ago; the Age of
Reptiles.
– Earth’s surface changed dramatically during the
Mesozoic Era. Pangaea broke into smaller
continents, and the climate was warm and humid.
– Lizards, turtles, snakes and dinosaurs flourished
during this era.
3 periods of the Mesozoic Era :
– Triassic
– Jurassic
– Cretaceous Periods.
• The Triassic period marked the appearance of
dinosaurs. Most dinosaurs were about 4 m to 5 m long
and moved very quickly.
The Jurassic Period
• Two major groups of dinosaurs evolved during the
Jurassic Period: the saurischians, or “lizard-hipped”
dinosaurs, and the ornithischians, or “bird-hipped”
dinosaurs.
• Brontosauruses, now called Apatosauruses were
saurischians. Stegosauruses and Pterosaurs were
ornithischians.
The Cretaceous Period
– Among the common Cretaceous dinosaurs were
the Tyrannosaurus Rex, the ankylosaurs, the
ceratopsians, and the hadrosaurs.
The Cretaceous-Tertiary Mass Extinction
– The Cretaceous Period ended in another mass
extinction. No dinosaur fossils have been found in
rocks that formed after the Cretaceous Period.
– Many scientists accept the impact hypothesis as the
explanation for the extinction of the dinosaurs. This
hypothesis is that about 65 million years ago, a
giant meteorite crashed into Earth.
Cenozoic Era - current geologic era, which
began 65.5 million years ago;
– the Age of Mammals
– dramatic changes in climate have occurred.
As temperatures decreased during the ice
ages, new species that were adapted to life in
cooler climates appeared.
– Mammals became the dominant life-form and
underwent many changes.
• The Cenozoic Era is divided into two
periods: the Tertiary Period and the
Quaternary Period.
Fossil evidence for Gondwanaland