History of Earth
Differentiation of Early Earth
• 1. What caused the early Earth to be in a molten state?
• As the earth condensed during its early stages of formation, gravity
caused the rocky fragments and planetesimals to accelerate.
• This caused them to collide at high speeds, converting kinetic energy
into thermal energy.
• Additionally, the collision of asteroids, comets, and more
planetesimals onto the earth's surface provided heat.
• There is also an internal heating associated with radioactive decay.
• These processes caused the early earth to become so hot that it
became a hot mass of molten matter.
• 2. Why are iron and nickel found in the core?
• Due to gravitational force, denser substances as iron and nickel sink
toward the center in a process called planetary differentiation.
• the less dense materials such as sodium, potassium, calcium, and
silicates moved upwards from the mantle to the crust.
• This separation of materials creates the compositionally distinct layers
of earth, each with their unique physical and chemical behavior.
Relative Dating and Absolute Dating
• How did scientists piece together the events that happened millions
or billions of years ago, long before humans ever existed?
• Geologists reconstruct the sequence of events from the study of
petrology, stratigraphy, and paleontology.
• PETROLOGY is a branch of geology that deals with the origin,
composition, structure, and classification of rocks.
• STRATIGRAPHY is the study of rock layers (strata) and layering
(stratifications).
• PALEONTOLOGY studies the life that existed prior to, or sometimes at
the start of, the Holocene epoch.
• Based on the information
gathered from the study
of rock composition and
structure, rock layers,
and fossils, geologists
developed the GEOLOGIC
TIME SCALE.
• It represents the interval of
time occupied by the
geologic history of earth.
• It provided a meaningful
time frame wherein events
of geologic past are
arranged.
Two ways in which scientists piece together the
events and measure geologic time:
•Relative •Absolute
Dating Dating
Relative Dating
•Relative dating places •It simply means that
events or rocks intheir Event B occured
chronological before Event C, but
sequence or order of after Event A.
occurence without
knowing its actual age.
Principle of original horizontality
• Sedimentary rocks are
deposited as horizontal
or nearly horizontal
layers. Any deviation
from horizontality
indicates that
deformation occurs after
the deposition.
Principle of superposition
• In the sequence of
sedimentary rocks, the
layer at the bottom of
the sequence is the
oldest, and the
successively higher
levels are successively
younger.
Principle of cross-cutting relationship
•Geologic features such
as faults or igneous
intrusion is younger
than the rocks that
they cut across
Principle of
inclusion
• If rocks or rock fragments
are included within
another rock layer, the
rock fragments must be
older than the rock layer
they were embedded
therefore anytime pperiod
can be recognized by its
fossil content.
Unconformities
• An unconformity is a surface
that corresponds with a gap in
sedimentation resulting from
nondeposition or erosion.
• Rocks above any unconformity
are younger than those below it.
Correlation of Rock Layers
• If the rock prints are of the • Equivalence is based on
same type and look similar, lithologic similarity and
then they may correlate. fossils.
• If the rocks are equivalent, • Fossils are key indicators
they may have the same of relative as well as
relative age depositional environment.
Absolute Dating
• Absolute dating places • Decay rate is described in
actual ages of rocks and terms of half-life.
events. • A half-life is the time
• The method used is required for half of the
radiometric dating nuclei to undergo
technique based on the radioactive decay.
decay rate of certain
radioactive nuclides within
fossils, rocks, and any
artifact.
• The use of radiometric dating • 3. the majority of the 70 dated
meteorites have ages that range
method revealed the following from 4.5 to 4.6 billion y/o
informations: • 4. the age f earth using isotopes
of lead is 4.54 billion y/o.
• 1. the oldest rocks on earth found
in Greenland are 3.7 to 3.8 billon • Radiometric dating is also used
y/o in determing the ages of fossils,
early man and mineral deposits,
• 2. the oldest moon rocks taken by recurrence rates of volcanic
the Apollo Missin were found to eruptions and earthquakes,
be 4.4 to4.5 billion y/o reversals of earth's magnetic
field and age and duration of
geologic events and processes.
Based on the sequence of layers, the relative age
of the layers would be as follows:
• Laguna • Cavite
• diskettes layer (youngest) • diskettes layer (youngest)
• aluminum cans layer • aluminum cans layer, 1970
• ceramic cups layer ID card
• tin cans layer, 1950 LP • tin cans layer
• stone tools layer (oldest) • stone tools layer (oldest)
• The excavation sites
contain some clues to the
absolute age
• In the Laguna site, a 1950
license plate is found on
the tin cans layer.
• In the Cavite site, a 1970
ID card is found in the
aluminum cans layer.
•Make a relative time •After making a
scale of seven relative time scale,
important events that assign dates to your
have occured in your seven listed events.
lifetime. These events This is an absolute
only show time scale.
chronological order.
