Deck 12: The Hadean and Archean Eons of Precambrian Time

Question 1

Regional metamorphism affected Proterozoic cratons in a process called

A) suturing of a microplate.
B) orogenic stabilization.
C) remobilization.
D) continental accretion.

Answer 1

C

Question 2

Gowganda mudstones in Canada show evidence of glacial melting at sea or in a large lake in the form of

A) faceted pebbles and cobbles.
B) dropstones.
C) non-laminated mudstones.
D) stromatolites.

Answer 2

B

Question 3

Thought to be the __________ of dinoflagellates, the __________ are the most common fossil algal plankton of Proterozoic rocks younger than 2 billion years.

A) biomarkers; stromatolites
B) resting cysts; acritarchs
C) chloroplasts; eukaryotes
D) cytoskeletons; bacteria

Answer 3

B

Question 4

From rocks formed at the time of the Archean-Proterozoic transition (2.5 billion years ago), there is evidence

A) that an abrupt change in the nature of life on Earth had occurred.
B) of a decline in the offshore, cone-shaped cyanobacterial mounds.
C) of an abrupt increase in the growth of stromatolites produced by cyanobacteria.
D) that eukaryotic algae existed, but cyanobacteria remained more abundant.

Question 5

In Neoproterozoic rocks about 570 million years old, evidence of multicellular animal life called the Ediacara fauna consists of

A) imprints of soft-bodied organisms.
B) resting stages (or cysts) of dinoflagellates.
C) trace fossils, imprints of soft-bodied fossils, and skeletal fossils.
D) small skeletonized animals.

Question 6

What evidence below does NOT suggest that the Wopmay orogen had the same pattern of formation as a modern orogenic system?

A) There is a succession of parallel igneous, metamorphic, and fold-and-thrust belts occurred.
B) Shallow shelf deposits are covered by molasse deposits, which lie upon flysch deposits.
C) Within fold-and-thrust belts, flysch deposits are succeeded upward by shallow-water shelf deposits.
D) Enormous stromatolite mounds grew at the top of lagoonal dolomite sequences.

Question 7

The Ediacaran fossil Spriggina was likely an early form of

A) fish.
B) arthropod.
C) mollusk.
D) cnidarian.

Question 8

The Ediacaran fossil with three-fold symmetry that may be related to modern echinoderms with five-fold symmetry is

A) Charnia.
B) Dickinsonia.
C) Tribrachidium.
D) Mawsonites.

Question 9

Cratons of modern proportions first began to form during

A) Neoproterozoic.
B) Mesoproterozoic.
C) Paleoproterozoic.
D) Late Archean.

Question 10

Animals probably originated during

A) Paleoproterozoic.
B) Mesoproterozoic.
C) Neoproterozoic.
D) Early Paleozoic.

Question 11

Until at least halfway through Paleoproterozoic (about 1.2 billion years ago), the main producers in Earth's marine ecosystems were

A) dinoflagellates.
B) multicellular algae.
C) eukaryotic algae.
D) bacteria, including cyanobacteria.

Question 12

The transition from shelf deposition to deepening associated with the onset of continental collision is marked by a change from

A) cross-bedded orthoquartzites and quartz pebblestones to stromatolitic shaly and cherty dolomites.
B) silty mudstone and turbidites to laminated and concretionary shale.
C) stromatolitic shaly and cherty dolomites to silty mudstone and turbidites.
D) laminated and concretionary shale to laminated shaly limestone with turbidites.

Question 13

The Wopmay orogeny, involving the Slave craton and an island arc, tells us that

A) the Proterozoic crust was still hot and plastic like the Archean crust.
B) there were no glaciers were present on Earth at this time.
C) Proterozoic orogenies are much like Phanerozoic orogenies.
D) it does no good to look for Proterozoic flysch and molasse deposits.

Question 14

Proterozoic "elephant skin" bedding surfaces indicates

A) ripples in sediment of the sea floor.
B) shrinkage of thread-like cyanobacterial mats.
C) burrows kept open for communication with oxygen-rich water.
D) horizontal burrows produced by some of the oldest known burrowing organisms.

Question 15

The bilaterally symmetrical soft-bodied Ediacaran fossil Kimberella is thought to represent the modern __________ group.

A) ecdysiozoan
B) lophotrochozoan
C) deutorozoan
D) dinoflagellate

Question 16

In the Wopmay orogenic sequence of sediments, the oldest sediments are

A) quartz sandstone that grades westward into deep-water mudstones and turbidites.
B) flysch deposits, mainly turbidites, overlain by mudstones.
C) river deposits with conspicuous cross-bedding.
D) carbonate rocks that contain abundant stromatolites.

Question 17

It is likely that the intracellular body within single-celled eukaryotes, which is called a chloroplast, was originally

A) a stromatolite.
B) a cyanobacterial cell.
C) some DNA and RNA.
D) a mitochondrion.

Question 18

The main exposed part of the North American craton (Laurentia), which was assembled from at least five microcontinents between 1.95 and 1.85 billion years ago, is called the

A) Appalachian orogen.
B) Cordilleran orogen.
C) Canadian shield.
D) Colorado plateau.

Question 19

The key evolutionary step that allowed one cell to engulf another was the

A) absorption of mitochondria.
B) retention of chloroplasts.
C) development of a cytoskeleton.
D) evolution of photosynthesis.

Question 20

The Neoproterozoic radiation of large, conspicuous animals a few million years __________ suggests that there may have been a connection.

A) after the third major ice age of the Neoproterozoic
B) before the first Neoproterozoic ice age
C) after the end of the second Neoproterozoic ice age
D) after the Neoproterozoic decline in atmospheric oxygen

Question 21

The Proterozoic orogeny that built mountains along the east coast of North America is called

A) Wopmay.
B) Trans-Hudson.
C) Grenville.
D) Cordilleran.

Question 22

Africa was assembled in the Pan-African orogeny during

A) Neoproterozoic.
B) Mesoproterozoic.
C) Paleoproterozoic.
D) Archean.

Question 23

__________ is a continental craton that was NOT part of Gondwanaland.

A) Africa
B) Laurentia
C) South America
D) Australia

Question 24

The 1.85-billion-year-old Sudbury impact crater contains

A) spherical, sand-sized grains that were originally glassy.
B) megabreccia and shatter cones.
C) large, elongate clasts that formed as airborne globs of melted material.
D) banded iron formations and cherts.

Question 25

The Paleoproterozoic buildup of atmospheric oxygen resulted in

A) resumed deposition of banded-iron formations.
B) deposition of limestones with isotopically heavy carbon.
C) oxidation of vast amounts of organic carbon.
D) climatic change that brought on "snowball Earth."

Question 26

The great Proterozoic supercontinent, which was split apart beginning about 720 million years ago, is called

A) Nuna.
B) Rodinia.
C) Pannotia.
D) Gondwanaland.

Question 27

In the Rodinia of 800 million years ago, the area of Laurentia is bordered on the east by

A) South China.
B) Grenville orogenic belt.
C) Antarctica.
D) Australia.

Question 28

The Proterozoic Keweenawan basalts

A) covered much of the Canadian Shield.
B) formed in the closing ocean between Greenland and Canada.
C) formed in the island arc that collided with the Slave Province.
D) erupted in a great, elongate rift that could have pulled North America apart.

Question 29

Cap carbonates resting directly on all three Neoproterozoic tillites indicate that perhaps

A) glaciers of "snowball Earth" reached the tropics.
B) submarine volcanism ceased and with it carbon dioxide release as well.
C) there was a mass extinction occurred among the cyanobacteria.
D) frozen methane hydrates suddenly thawed out.

Question 30

The Paleoproterozoic shift at about 1.85 billion years ago from banded-iron formations to red beds signals the

A) demise of the cyanobacteria and the rise of the eukaryotic algae.
B) effects of the gigantic asteroid impact at Sudbury and its global ejecta.
C) buildup of significant oxygen in the atmosphere and oceans.
D) transition from flysch to molasse deposition in many large basins.