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Geologic Time
Geologic Time
•
The first geologic time scale was proposed
in 1913 by the British geologist Arthur
Holmes (1890 - 1965). This was soon after
the discovery of radioactivity, and using it,
Holmes estimated that the Earth was
about 4 billion years old - this was much
greater than previously believed.
The Divisions of Precambrian
Time
Precambrian Era
• 4.6 billion years ago, the Earth was born.
• Nearly 4 billion years passed after the
Earth's inception before the first animals.
This stretch of time is called the
Precambrian.
• It makes up roughly seven-eighths of the
Earth's history
• During the Precambrian, the most
important events in biological history took
place.
Precambrian Era
• The Earth formed, life arose, the first
tectonic plates arose and began to
move, eukaryotic cells evolved, the
atmosphere became enriched in
oxygen -- and just before the end of
the Precambrian, complex multicellular organisms, including the first
animals, evolved.
Precambrian Earth
Precambrian Era
• Also divided into different Eons:
–Hadean – Earths creation
–Archean – Earliest Rocks form
–Proterzoic - First organisms with
well-developed cells form.
Paleozoic Era Divisions
Paleozoic – “Ancient Life”
The Paleozoic Era
• At its beginning, multi-celled animals
underwent a dramatic explosion in
diversity, and almost all living animal phyla
appeared within a few millions of years.
• At the other end of the Paleozoic, the
largest mass extinction in history wiped
out approximately 90% of all marine
animal species. The causes of both these
events are still not fully understood
Paleozoic Era
• The Paleozoic took up over 300 million
years.
• During the Paleozoic there were six major
continental land masses.
• These Paleozoic continents experienced
tremendous mountain building along their
margins, and numerous incursions and
retreats of shallow seas across their
interiors.
Gondwana and the Continental
Landmasses During Paleozoic Period
Cambrian Period
• "Age of Trilobytes" -The Cambrian
Explosion of life occurs; all existent phyla
develop. Many marine invertebrates
• First vertebrates. Earliest primitive fish.
Mild climate.
• Mass Extinction of trilobites and nautiloids
at end of Cambrian (50% of all animal
families became extinct), probably due to
glaciation.
The Cambrian Sea
Ordovician Period
Ordovician Period
• First corals.
• Primitive fishes, seaweed and fungi.
Graptolites, bryozoans, gastropods,
bivalves, and echinoids.
• High sea levels at first, global cooling and
glaciation, and much volcanism.
• North America under shallow seas. Ends
in huge extinction, due to glaciation.
Silurian Period
Silurian Period
• Primitive plants appear on land.
• The first jawed fishes
• First vascular plants (plants with waterconducting tissue) appear on land
• High seas worldwide. Brachiopods,
crinoids, corals.
• First insects appeared.
Devonian Period – Age of Fishes
Devonian
Devonian Period
"The Age of Fishes"
• Fish and land plants become abundant
and diverse.
• First amphibians appear (evolved from
the lungfish). First sharks, and bony fish.
• Many coral reefs, brachiopods, crinoids.
• New insects appeared.
• Mass Extinction (345 mya) wiped out
30% of all animal families) probably due to
glaciation or meteorite impact
Carboniferous Period
Carboniferous Period
(Mississippian & Pennsylvanian)
• Wide-spread coal swamps and many
ferns.
• Appalachian Mountains form.
• Amphibians become more common.
• First true reptiles.
• The first cockroaches appear
• First winged insects
Model of a Pennsylvanian
Coal Swamp
Mountains formed during this
period
Amphibians of the Permian Period
Permian Period
"The Age of Amphibians"
• Amphibians and reptiles dominant.
• Gymnosperms dominant plant life.
• The continents merge into a single supercontinent, Pangea.
• Phytoplankton and plants oxygenate the Earth's
atmosphere to close to modern levels.
• The Permian ended with largest mass
extinction. Trilobites go extinct, as do 50% of all
animal families, 95% of all marine species, and
many trees, perhaps caused by glaciation or
volcanism
Late Paleozoic Plate Movements
Mesozoic Era
245 – 208 MYA
Mesozoic Era
• The Mesozoic is divided into three time
periods:
– the Triassic (245-208 Million Years Ago),
– the Jurassic (208-146 Million Years Ago),
– and the Cretaceous (146-65 Million Years
Ago).
• Mesozoic means "middle animals", and is
the time during which the world fauna
changed drastically from that which had
been seen in the Paleozoic.
Mesozoic Era
• Dinosarus, evolved in the Triassic, but were not
very diverse until the Jurassic.
• Except for birds, dinosaurs became extinct at the
end of the Cretaceous.
• The Mesozoic was also a time of great change
in the terrestrial vegetation. The early Mesozoic
was dominated by ferns, cycads
• Modern gymnosperms, such as conifers, first
appeared
• By the middle of the Cretaceous, the earliest
angiosperms had appeared
Mesozoic Plant Life
Dinosaurs of the Triassic Period
Triassic Period
• The first dinosaurs, mammals, and
crocodiles appear.
• Mollusks are the dominant invertebrate.
• Many reptiles, for example, turtles.
• True flies appear.
• Triassic period ends with a minor
extinction 213 mya (35% of all animal
families die out, including marine reptiles).
This allowed the dinosaurs to expand
Jurassic Period
Jurassic Period
•
•
•
•
Many dinosaurs, including the giants.
The first birds appear (Archaeopteryx).
The first flowering plants evolve.
Many ferns, cycads, gingkos, rushes,
conifers,
• Flying reptiles, pterosaurs.
• Minor extinctions at 190 and 160 mya.
Earth During the Jurassic Period
Life of the Cretaceous Period
Cretaceous Period
• The heyday of the dinosaurs.
• The earliest-known butterflies appear as well as
the earliest-known snakes, ants, and bees.
• High tectonic and volcanic activity.
• Primitive marsupials develop.
• Continents have a modern-day look.
• Ended with large extinction (the K-T extinction)
of dinosaurs, pterosaurs, ammonites, about 50
percent of marine invertebrate species, etc.,
probably caused by asteroid impact or volcanism.
What happened to the dinosaurs?
Asteroid?
Volcanoes?
Glaciers?
Cenozoic Era
65 MYA to Present
Cenozoic Era the Age of Mammals
Cenozoic Era
• The Cenozoic is the most recent of the
three major subdivisions of animal history.
• The Cenozoic is called the Age of
Mammals, because the largest land
animals have been mammals during that
time.
• The Cenozoic is divided into two main
sub-divisions: the Tertiary and the
Quaternary.
Tertiary Mammals
Tertiary Period
• First large mammals and primitive
primates,
• Mammals abound. Rodents appear.
Mammals return to the sea.
• Flower plants thrive.
• More mammals, including the horses,
dogs and bears. Modern birds.
• First hominids (australopithecines).
• Continental glaciers repeatedly cover NA
Quaternary Period
• The first humans (Homo Sapiens) evolve.
Mammoths, mastodons, saber-tooth
tigers, giant ground sloths.
• A mass extinction of large mammals and
many birds happened about 10,000 years
ago, probably caused by the end of the
last ice age.
• Human civilization
Early Man – Quaternary Period
Geologic Time Scale of Kentucky
Bluegrass Geology
The bedrock in the center (Bluegrass Region) of the State is composed of
limestones and shales from the Ordovician Period (510 to 440 million years ago).
The oldest rocks at the surface in Kentucky are limestones from the Late
Ordovician Period (approximately 450 million years ago), which are exposed
along the Palisades of the Kentucky River (for example, near Camp Nelson, in
Jessamine County, pictured above).
Ordovician fossils are abundant in many areas.