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Earth’s History
Vocabulary
geologic time
• Geological time is a
system of
chronological
measurement that
relates layers of rock
to time, and is used
by geologists,
paleontologists, and
other Earth scientists
to describe the timing
and relationships
between events that
have occurred
throughout Earth's
history.
chronology
• the arrangement of events or dates in the
order of their occurrence.
• the study of historical records to establish the
dates of past events.
Eons and Eras
• Eon - an indefinite and
very long period of
time
• Era - a long and
distinct period of
history with a
particular feature or
characteristic. A major
division of time that is
a subdivision of an eon
and is itself subdivided
into periods.
Period and Epoch
• Period - A geologic
period is one of
several subdivisions
of geologic time
enabling crossreferencing of rocks
and geologic events
from place to place.
• Epoch - a division of
time that is a
subdivision of a period
and is itself subdivided
into ages,
corresponding to the
geologic record
Stratigraphy
• the branch of geology concerned with the order
and relative position of rock layers and their
relationship to the geological time scale.
• the analysis of the order and position of layers of
archaeological remains.
• the structure of a particular set of rock layers.
Mass extinctions
• A mass extinction is a relatively sudden, global decrease
in the diversity of life forms.
• Mass extinctions have occurred periodically throughout
the existence of life on Earth.
• To be a mass extinction, the following must occur:
Extinctions occur all over the world. A large number of
species go extinct.
Fossils
• Fossil - the remains
or impression of a
prehistoric organism
preserved in petrified
form or as a mold or
cast in rock.
• Index fossil - a fossil
that is useful for
dating and
correlating the strata
in which it is found.
Relative age
• To determine the relative age of different rocks,
geologists start with the assumption that unless
something has happened, in a sequence of
sedimentary rock layers, the newer rock layers
will be on top of older ones.
• relative age dating is like saying that your
grandfather is older than you.
Absolute age
• With absolute age dating, you get a real age in
actual years. It’s based either on fossils which are
recognized to represent a particular interval of
time, or on radioactive decay of specific isotopes.
• Absolute age dating is like saying you are 15 years
old and your grandfather is 77 years old.
Law of Superposition
• states that in any
undisturbed sequence of
rocks deposited in layers,
the youngest layer is on top
and the oldest on bottom,
each layer being younger
than the one beneath it
and older than the one
above it.
• Based on the Rule of
Superposition, certain
organisms clearly lived
before others, during
certain geologic times.
After all, a dinosaur
wouldn’t be caught dead
next to a trilobite.
Igneous rock
• Igneous rock is formed through the cooling
and solidification of magma or lava.
Pangaea
• Pangaea was supercontinent that included all
current land masses, believed to have been in
existence before the continents broke apart
during the Triassic and Jurassic Periods.
Uniformitarianism
• the theory that changes in the earth's crust
during geological history have resulted from
the action of continuous and uniform
processes.
ice core
• An ice core is a core sample that is typically
removed from an ice sheet, most commonly
from the polar ice caps of Antarctica,
Greenland or from high mountain glaciers
elsewhere.
• Watch the following video
• http://www.livescience.com/14672-ice-coresview-earth.html