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GEOLOGIC
TIME
James Ussher
 concluded that Earth was
only FOUR THOUSAND YEARS
OLD
Catastrophism
Earth's
landscapes had
been developed
primarily by great
catastrophes
Modern Geology
Introduced the principle of
UNIFORMITARIANISM
The process we observe
presently now have always
been operated in the past.
"The present is the key
to the past"
James Hutton
Relative Dating
 determining relative order in the past
without necessarily determining their
age
 placing rocks and events in sequence
Principles and rules
 Law of Superposition
 Principle of Original Horizontality
 Cross-cutting Relationship
 Law of Inclusion
 Unconformities
Law of Superposition
oldest rocks are at the bottom
Youngest
Oldest
Principle of Original Horizontality
Cross-cutting Relationship
 younger features that cuts across
through a sequence an older feature
 any feature that cuts across a
sequence of rock, is younger than
everything it cuts
Law of Inclusions
pieces of one rock unit that are
contained within another
Unconformities
 a break in the rock record
represent the long period during which
deposition ceased, erosion removed
previously formed rocks, then deposition
resumed.
Types of Unconformities
 Angular Unconformity
 Disconformity
 Nonconformity
Angular Unconformity
 is an erosional surface on tilted or
folded strata, over which younger strata
have been deposited
Disconformity
A surface of erosion or non-deposition
between Parallel sedimentary rock beds of
differing ages
Nonconformity
 is an erosional surface on igneous or
metamorphic rocks which are overlain by
sedimentary rocks.
Correlation of Rock Layers
 Matching rocks
of the same age
in different
regions.
End . . .
Fossils:
Evidence of
past life
• Arien P. Avenasa
• Remains or traces of prehistoric life
• Important basic for interpreting the geologic past
Paleontology vs. archeology
• Paleontologists study fossils and are concerned with all lifeforms in the geologic past. By contrast, archaeologists focus on
the material remains of past human life. (i.e. sites, buildings,
artifacts)
Paleontologist = geology + biology  succession of life over the vast
expanse of geologic time
Type of fossils
• Unaltered remains
• Petrified (literally, “turned into stone”)
• Replacement
• Molds and Casts
• Carbonization
• Amber
• Tracks
• Burrows
• Coprolites
• Gastroliths
Under what circumstances are they
preserved?
• Rapid burial (the remains are buried by
sediment. When this occurs, the remains are
protected from the environment, where
destructive processes operate. Therefore,
rapid burial is an important condition favoring
preservation.)
• Possession of hard parts. (Hard parts such as
shells, bones, and teeth predominate in the
record of past life.)
principle of fossil succession
• (Fossil organisms succeed one another in a definite and
determinable order; and therefore any time period can
be recognized by its fossil content.)
• Index fossils - these fossils are widespread
geographically and are limited to a short span of
geologic time, so their presence provides an important
method of matching rocks of the same age.
Basic atomic
structure
Protons = positive
charge
Neutron = neutral
Electron = negative
charge
Alpha Emission
Radioactivity
Beta Emission
Electron
Capture
Three types of
radioactive decay
• ATOMIC NUMBER: number of
protons in the nucleus
• ATOMIC MASS NUMBER: protons
+ neutrons
RADIOACTIVITY
CALCULATING THE
AGES OF ROCKS
AND MINERALS
THAT CONTAIN
PARTICULAR
RADIOACTIVITY
ISOTOPESDECAYING AT A FIXED
RATE SINCE THE
FORMATION OF THE
ROCKS
PRODUCTS OF DECAY
HAVE BEEN
ACCUMULATING AT A
CORRESPONDING RATE
A CORRECT DATE IS NOT
POSSIBLE UNLESS THERE
WAS NEITHER THE
ADDITION NOR LOSS OF
PARENT OR DAUGHTER
ISOTOPES.
ADIOCARBON DATING
• TO MEASURE RECENT EVENTS
• HALF LIFE OF CARBON – 14 IS
ONLY 5,730 YEARS, IT CAN BE
USED FOR DATING EVENTS
FROM THE HISTORIC PAST AS
WELL AS THOSE FROM VERY
RECENT GEOLOGIC HISTORY.
• CARBON -14 Carbon- 14 is
continuously produced in the
upper atmosphere as a
consequence of cosmic-ray
bombardment.
THE END 
The Geologic Time
Scale
by: Yves Mariene L.
Dela Peña
Geological Time Scale
• Divides Earth's history into
units of varying magnitude.
• Used by scientist to describe
the timing and relationships
between events that have
occured during the history of
Earth.
Structure of the Time Scale
• Eons- represent the greatest
expanses of time.
• Phanerozoic- a term Derived
from the Greek words
meaning "visible life."
• -contain abundant fossils that
document major evolutionary
trends
Three eras within the
Phanerozoic:
• Paleozoic (ancient life), Mesozioc (middle life),
and Cenozoic (recent life)
• Each era of Phanerozoic econ is subdiveded
into periods
• Each periods is divided into smaller units called
epochs
The Geologic Time Scale
Quaternary
Latin, “fourth”
1822
Tertiary
Latin, “third”
1760
Cretaceous
Latin creta, “chalk”
1822
Jurassic
Jura Mountains, Switzerland
1795
Triassic
Latin, “three-fold”
1834
Permian
Perm, Russia
1841
Carboniferous
Carbon-bearing
1822
Devonian
Silurian
Devonshire, England
Silures, a pre-Roman tribe
1840
1835
Ordovician
Ordovices, a pre-Roman tribe
1879
Cambrian
Latin Cambria, “Wales”
1835
Precambrian Time
• Precambrian- represent about
88 percent of Earth history
• 4 billions years prior to the
Cambrian is divided into three
econs:
• Hadean
• Archean
• Proterozoic
Terminology and the Geologic
Time Scale
• Precambrian- the informal name for the
econs that came before the current
Phanerozoic econ.
• Hadean- is another infromal term that is
found on some versions of the geologic
time scale and is used by some
geologists.
Difficulties in Dating the
Geologic Time Scale
• Samples of sedimentary rock can
only rarely be dated directly by
radiometric means. The rock's age
cannot be accurately determined
because the grains making up the
rock are not the same age as the
rock in which they occur.
Rather,the sediments have been
weathered from rocks of diverse
ages
• Radiometric dates obtained from
metamorphic rocks may also be
difficult to interpret because the
age of a particular mineral in a
metamorphic rock does not
necessarily represent the time
when the rock initially formed.
Instead, the date may indicate
anyone of a number of
subsequent metamorphic
phases.
• Dendrochronology-The dating and
study of annual rings in trees
• Cross dating- by matching the ring
pattern common to both sample.
• Tree-ring
–chronologies are unique
archieves of environmental
history and have important
applications in such disciplines
as climate, geology, ecology and
archaeology.
Weather
which
encourages
narrow treering growth
Weather
which
encourages
wide tree-ring
growth
Harsh
winter
mild winter
Hot summer
mild
summer
drought
wet summer
Is Earth Unique?
There
is only one place in the
universe, as far as we know,
that can support life—a
modest-sized planet called
Earth that orbits an
average-sized star, the Sun.
The Right Planet
 Its
force of gravity would be
proportionately greater.
 Like the Moon and Mercury, both of
which lack an atmosphere, Earth would
be void of life.
 The entire planet would likely he covered
by an ocean a few kilometers deep.
 The fact that if our planet did not have a
molten metallic core, most of the lifeforms on Earth would not exist.
The Right Location
 10
percent closer to the Sun, like
Venus, our atmosphere would consist
mainly of the greenhouse gas carbon
dioxide.
 10 percent farther from the Sun, the
problem would be reversed—it would
be too cold.
 Near a star of modest size. Stars like
the Sun have a life span of roughly 10
billion years.
The Right Time
Microorganisms
evolved that
released oxygen into the
atmosphere by the process of
photosynthesis.
Habitats, along with evolutionary
forces, led to the development of
many large mammals that occupy
our modern world.
Birth of a Planet
 Big
Bang theory - formation of our planet
began about 13.7 billion years ago with a
cataclysmic explosion that created all matter
and space.
 Big Bang scenario, atoms in your body were
produced billions of years ago in the hot
interior of now defunct stars, and the
formation of the gold in your jewelry was
triggered by a supernova explosion that
occurred trillions of miles away.
From Planetesimals to
Protoplanets
Solar
nebula
Planetesimals
Protoplanets
Earth's Early Evolution
Formation Of Early Earth
Origin of the
Atmosphere and
Oceans
• By: Sabellano
The air we breathe is a stable
mixture of 78% nitrogen, 21%
oxygen, about 1%argon (an
inert gas), and small amount
of gases such as carbon
dioxide and water vapor.
Earth’s Primitive
Atmosphere
Early in the Earth’s
formation, it consisted of
gases like hydrogen, helium,
methane, ammonia, carbon
dioxide and water vapor.
Hydrogen and helium are the
lightest of these gases.
Earth’s gravity was too weak
to hold those light gases. Most
of the gases were probably
scattered into space by strong
solar winds from a young
active sun.
Earth’s first enduring
atmosphere was generated
by a process called
outgassing. In which gases
trapped in the planet’s
interior are released.
Oxygen in the
Atmosphere
During this period of
intense, Earth became hot
enough that iron and nickel
began to melt. Occurs
rapidly on the on the scale
of geologic time and
produced Earth’s dense ironrich core.
This period differentiation
established the three major
division’s of Earth’s interior:
rich core, the thin primitive
crust, and the Earth’s
thickest layer, the mantle.
Evolution of the
Oceans
Precambrian History:
The formation of
Earth's Continents
Precambrian
History
The
Precambrian History, which is divided into the
Archean and Proterozoic eons, spans almost 90% of
Earth’s history.
Much of Earth’s stable continental crust was
created during this time
The Archean is the name of the age which
began with the forming Earth. Following
the Hadean Eon and preceding
the Proterozoic Eon. During the Archean,
the earth's crust and layers had just
formed, making the Earth much cooler than
it was during the Hadean and allowing the
formation of continents.
The Proterozoic is a geological eon representing
the time just before the proliferation of complex life
on Earth. The name Proterozoic comes from Greek
and means "earlier life", the Greek root protero
,means "former, earlier" and zoic- ,means "animal,
living being".
is the most recent part of the Precambrian.
Precambrian History
Partial melting of the mantle formed
volcanic islands arc and ocean plateaus.
These crustal fragments collided and
accreted to form larger crustal provinces .
Precambrian History
Larger crustal areas were assembled into larger
blocks called cratons.
Cratons form the core of modern continents.
Precambrian History

Supercontinents
Large landmasses that consist of all , or nearly all,
existing continents.
Pangaea was the most recent, but perhaps and even
larger one, Rodinia, preceded it.
Splitting and reassembling of supercontinents have
generated most of Earth’s major mountain belts.
Supercontinents have also profoundly affected Earth’s
climate over time.
PANGEA
Rodinia
Geologic History of
the Phanerozoic:
Formation of Earth’s
Modern Continents
Ebal, Queennie Joy J.
PHSC 9:00-10:30 TTH
Phanerozoic Era
- The time span since the close of the Precambrian period
- Encompasses 542 million years and is divided into 3 eras:
Paleozoic
Mesozoic
Cenozoic
- The study of Phanerozoic crustal history was aided by the availability of
fossils, which improved our ability to date and correlate geologic events.
First life-forms
with hard parts
such as shells,
scales, bones, or
teeth—all of
which greatly
enhance the
possibility of an
organism being
preserved in the
fossil record
Paleozoic History
- North America hosted no living things
- The continent was largely a barren lowland
- One of the major events was the formation of the
supercontinent: PANGAEA
Formation of Pangaea
- began with a series of collisions that
gradually joined North America, Europe,
Siberia, and other smaller crustal fragments
LAURASIA - large northern
continent
GONDWANA encompassed five
continents-—South
America, Africa, Australia,
Antarctica, India and
perhaps portions of China
Mesozoic History
Spanning about 186 million years, the Mesozoic era is divided
into three periods: the
Triassic primarily red sandstones and mudstones that lack
marine fossils
Jurassic extensive continental sediments were deposited
Cretaceous formation of "coal swamps” similar to those of
the Paleozoic era
Navajo Sandstone, a crossbedded, quartz-rich layer,
that in some places
approaches 300 meters
(1,000 feet) thick.
Cenozoic History
Era of Recent Life
- encompasses the last 65.5 million years of Earth
history
- the rock formations are more widespread and less
disturbed than those of any preceding era.
- Volcanic activity was also common in the West during much
of the Cenozoic.
- The effects of mountain building, volcanic activity, isostatic
adjustments, and extensive erosion and sedimentation
created the physical landscape we know today.
HOW DID LIFE BEGIN?
REQUIREMENTS OF LIFE:
- Presence of hospitable environment
- Chemical raw materials that form the essential
molecules of DNA, RNA, proteins
- Amino Acids
Prokaryotes – 1st known
organisms
Anaerobic Metabolism – without
oxygen
Cyanobacteria – contributed rise
of
oxygen
Stromatolites – fossil evidence
of these
bacteria
Eukaryotes – multicellular
organisms
Paleozoic Era – emergence of a
spectacular variety of
new life-forms
Quaternary Period – humans
evolved,
actions of glacial
ice, wind and running water
added the finishing touches