Lesson 9: Stratigraphy and Geologic Time

Question 1

The tendency for rock layers to be

chronologically stacked is called the

Answer 1

Principle of Superposition.

Question 2

Stratigraphy is the

Answer 2

science of using the arrangement and composition of rock layers to interpret geological history.

Question 3

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

Answer 3

formation.

Question 4

When
a sequence of rock changes from one formation
to another, it indicates that a large scale change
occurred in

Answer 4

the environment where the rocks

were being deposited

Question 5

To age rocks in absolute terms, a

technique called __ is used.

Answer 5

radiometric dating

Question 6

An isotope is a

Answer 6

variant of a chemical
element that has an unusual number of
neutrons

Question 7

When a new rock forms, it has a ratio of

Answer 7

isotopes and decay products that matches that

of the environment.

Question 8

. 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

Answer 8

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

Question 9

The geologic time scale is a

Answer 9

standardized series of
chronological divisions that parses the Earth’s
history into discrete named units.

Question 10

The largest

units in the time scale are __, followed by __, __, and __.

Answer 10

Eons, Eras, Periods, and Epochs

Question 11

THE HADEAN EON

Answer 11

4.6 TO 4 BILLION YEARS AGO

Question 12

THE ARCHEAN EON

Answer 12

4 TO 2.5 BILLION YEARS AGO The oldest known fossils come from the THE ARCHEAN EON (cyanobacteria age)

Question 13

The Paleozoic Era

Answer 13

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

Question 14

THE PROTEROZOIC EON

Answer 14

2.5 BILLION TO 541 MILLION YEARS AGO. At approximately 1.7 billion years ago, the first
multicellular organisms evolved.

Question 15

Within the Proterozoic, the time span

from

Answer 15

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.

Question 16

THE PHANEROZOIC EON

Answer 16

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.

Question 17

The Cambrian Period

Answer 17

541 to 485 million years

ago

Question 18

The beginning of the Cambrian marks such a
dramatic diversification of aquatic animal life
that it is often referred to as

Answer 18

The Cambrian Explosion

Question 19

The Ordovician Period

Answer 19

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.

Question 20

The Silurian Period

Answer 20

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.

Question 21

The Devonian Period

Answer 21

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.

Question 22

The Carboniferous Period

Answer 22

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.

Question 23

The Permian Period

Answer 23

– 299 to 252
The continents collided together and formed a
single super continent called Pangaea.

Question 24

The Mesozoic Era

Answer 24

252 to 66 million years ago
The Mesozoic is often referred to as the Age of
Dinosaurs

Question 25

The Cenozoic Era

Answer 25

– 66 to 0 million years ago
The Cenozoic is often referred to as the Age of
Mammals.

Question 26

The Paleogene Period

Answer 26

66 to 23 million years
ago
Global temperatures began to cool. Mammals
diversified into a variety of new forms, including
primates, bats, and whales. Birds also
diversified.

Question 27

The Neogene Period

Answer 27

23 to 2.6 million years
ago
Global temperatures continued to cool. The first
hominids evolved in Africa.

Question 28

The Quaternary Period

Answer 28

2.6 to 0 million years
ago
The earth experienced several large glaciation
events, or “ice ages”. The first anatomically
modern humans evolved. Human civilization
spread.

Question 29

The Triassic Period

Answer 29

252 to 201 million years
ago
During the first ten million years of the Triassic,
life gradually recovered from the mass
extinction that occurred at the end of the
Permian.

Question 30

The Jurassic Period

Answer 30

– 201 to 145 million years
ago
Dinosaurs diversified. This was the peak of
sauropod diversity, and they were the dominant
terrestrial herbivores. The supercontinent Pangaea
began to break apart

Question 31

The Early Cretaceous Period

Answer 31

146 to 100
million years ago
Dinosaurs continue to diversify and the first
flowering plants evolved.

Question 32

The Late Cretaceous Period -

Answer 32

• 100 to 65 million years ago
  Often considered the apex of non-avian
  dinosaur diversity, many of the most famous
  dinosaurs come from this period of time