Lesson 9: Stratigraphy and Geologic Time Flashcards
The tendency for rock layers to be
chronologically stacked is called the
Principle of Superposition.
Stratigraphy is the
science of using the arrangement and composition of rock layers to interpret geological history.
A large
uninterrupted sequence of rock that is made of
multiple layers that all share similar properties
(such as mineral composition and average
sediment grain size) and that all formed under
similar conditions is termed a
formation.
When
a sequence of rock changes from one formation
to another, it indicates that a large scale change
occurred in
the environment where the rocks
were being deposited
To age rocks in absolute terms, a
technique called __ is used.
radiometric dating
An isotope is a
variant of a chemical
element that has an unusual number of
neutrons
When a new rock forms, it has a ratio of
isotopes and decay products that matches that
of the environment.
. If sedimentary rocks that contain
fossils are found between two horizontally
deposited layers of igneous rocks, then dating
the igneous rocks above the sedimentary layer
will tell us
what age the fossils must be older
than, and dating the igneous rocks below the
sedimentary layer will tell us what age the
fossils must be younger than
The geologic time scale is a
standardized series of
chronological divisions that parses the Earth’s
history into discrete named units.
The largest
units in the time scale are __, followed by __, __, and __.
Eons, Eras, Periods, and Epochs
THE HADEAN EON
4.6 TO 4 BILLION YEARS AGO
THE ARCHEAN EON
4 TO 2.5 BILLION YEARS AGO The oldest known fossils come from the THE ARCHEAN EON (cyanobacteria age)
The Paleozoic Era
541 to 252 million years ago. At the start of the Paleozoic, animal life was restricted to primitive invertebrates living in the oceans, but, by its close, great forests covered
the land and teamed with reptiles, amphibians,
and insects
THE PROTEROZOIC EON
2.5 BILLION TO 541 MILLION YEARS AGO. At approximately 1.7 billion years ago, the first
multicellular organisms evolved.
Within the Proterozoic, the time span
from
630 to 542 million years ago is known as
the Ediacaran Period. During the Ediacaran,
large forms of life with some harder parts
evolved, including the first animal life.
THE PHANEROZOIC EON
541 TO 0 MILLION YEARS AGO The Phanerozoic Eon is subdivided into three
eras, which are themselves subdivided into
numerous periods. It is during the Phanerozoic
that animal life rapidly evolved into a multitude
of diverse forms, including dinosaurs.
The Cambrian Period
541 to 485 million years
ago
The beginning of the Cambrian marks such a
dramatic diversification of aquatic animal life
that it is often referred to as
The Cambrian Explosion
The Ordovician Period
485 to 443 million years ago Global sea levels were high. Life in the oceans continued to diversify, with fish increasingly becoming the dominant large aquatic animals.
The Silurian Period
443 to 419 million years ago Until this point, fish had not yet evolved jaws. With the evolution of jaws came the evolution of large predatory fish. Primitive plant life
began to flourish on land.
The Devonian Period
419 to 359 million years ago The first forests appeared on land. Huge jawed fishes, like Dunkleosteus, evolved in the seas, and the first true sharks appeared. Lobe-finned
‘fishapods’, like Tiktaalik, ventured onto land,
and give rise to the tetrapods.
The Carboniferous Period
359 to 299 million
years ago
Amphibians were widespread in the abundant
swamps, and reptiles, the first amniotes,
evolved. Much of the coal that is mined today
formed from the rotting plants of Carboniferous
swamps.
The Permian Period
– 299 to 252
The continents collided together and formed a
single super continent called Pangaea.
The Mesozoic Era
252 to 66 million years ago
The Mesozoic is often referred to as the Age of
Dinosaurs
