Test 2 Chapter 12

Question 1

Explain why Earth is just the right size.

Answer 1

Earth is the right size to retain an atmosphere of the appropriate size to keep oxygen and
greenhouse gases in concentrations appropriate for life. If Earth were more massive, the
atmosphere would retain large amounts of ammonia and methane and would be too thick and too
hostile for life. If the Earth were smaller, the important gases, such as oxygen, would escape and
the planet would lack the atmosphere it currently has.

Question 2

In what way does Earth’s molten, metallic core help protect Earth’s life-forms?

Answer 2

The molten core allows for the existence of a magnetic field, which in turn protects life from
cosmic rays that would be lethal and would strip away the atmosphere.

Question 3

Why is Earth’s location in the solar system ideal for the development of complex life-forms like
humans?

Answer 3

The location of Earth in the solar system prevents it from being too hot (like Venus) or too cold
(like Mars). This ideal temperature allowed higher life to evolve over time.

Question 4

What two elements made up most of the very early universe?

Answer 4

The very early universe was made up mostly of hydrogen and helium

Question 5

Name the cataclysmic event in which an exploding massive star produces elements heavier than
iron.

Answer 5

Elements heavier than iron are formed at extreme temperatures during the explosive death of
large stars. These cataclysmic events are called supernova events

Question 6

Briefly describe the formation of the planets from the solar nebula.

Answer 6

The solar nebula was a large, rotating cloud of interstellar dust and gas. As the nebula
contracted, most of its matter collected in the center to form the protosun. The remaining
materials flattened into a rotating disk, and the matter in the disk gradually cooled and
condensed into masses of icy, rocky, and metallic materials. Through repeated collisions and
accretion, these masses became the planets we have today.

Question 7

Describe the conditions on Earth during the Hadean.

Answer 7

During the Hadean, Earth was mainly covered by a large magma ocean. Within this magma,
buoyant masses of molten rock rose to the surface to produce thin crustal rocks. The iron-rich
molten core formed during this time and through chemical differentiation, the major divisions of
Earth’s interior were formed

Question 8

What is meant by outgassing, and what modern phenomenon serves that role today?

Answer 8

Outgassing is the process through which gases trapped in the planet’s interior were released.
Today, hundreds of active volcanoes continue outgassing processes.

Question 9

List the most abundant gasses that were added to Earth’s early atmosphere through the process of
outgassing.

Answer 9

The most abundant gases added to Earth’s early atmosphere through outgassing were mainly
water vapor, carbon dioxide, and sulfur dioxide

Question 10

Why was the evolution of photosynthesizing bacteria important for the evolution of large oxygen
consuming organisms like ourselves?

Answer 10

Early photosynthesizing bacteria were responsible for adding oxygen to the oceans, and as the
number of these organisms increased, oxygen began to build in the atmosphere, making the
evolution of higher life-forms possible.

Question 11

Why was rainwater highly acidic in Earth’s early history

Answer 11

Early in Earth’s history, large amounts of sulfur dioxide were present in the atmosphere,
released from outgassing associated with large-scale volcanism. This sulfur dioxide combined
with water in the atmosphere to form sulfuric acid, creating the acidic rainwater.

Question 12

How does the ocean remove carbon dioxide from the Earth’s atmosphere? What role do tiny
marine organisms, such as foraminifera, play in the removal of carbon dioxide?

Answer 12

Carbon dioxide dissolved in seawater often joins other atoms or molecules to produce various
chemical precipitates. The most common compound generated by this process is calcium
carbonate (CaCO3), a mineral that makes up the shells and hard parts of many tiny marine plants
and animals. Foraminifera make their shells of calcium carbonate using carbon dioxide from
seawater, and, when they die, their shells accumulate on the seafloor and essentially “lock up”
carbon dioxide that was taken in from the atmosphere.

Question 13

Briefly explain how low-density continental crust was produced from Earth’s rocky mantle.

Answer 13

It is from Earth’s rocky mantle that low-density, silica-rich minerals were gradually distilled to
form continental crust. Partial melting of mantle rocks generates low-density, silica-rich
materials that buoyantly rise to the surface to form Earth’s crust, leaving behind the dense mantle
rocks.

Question 14

Describe how cratons came into being.

Answer 14

Craton formation begins with the collision and accretion of small crustal fragments. Deep in
these collision-formed fragments, partial melting generated silica-rich magmas that rose and
intruded the rocks above resulting in the formation of crustal provinces that, in turn, accreted
with other provinces into large crustal blocks called cratons.

Question 15

What is the supercontinent cycle? What supercontinent proceeded Pangaea?

Answer 15

The supercontinent cycle is the rifting and dispersal of one very large continent (supercontinent)
followed by a long period of time where the fragments are reassembled into a new supercontinent
with a different configuration. The supercontinent Rodinia preceded the supercontinent Pangaea

Question 16

Give an example of how the movement of a continent can trigger climate change.

Answer 16

As continents move, the patterns of ocean currents and global winds change, which influences the
global distribution of temperature and precipitation.

Question 17

Explain how the rate of seafloor spreading is related to changes in sea level.

Answer 17

When seafloor spreading rates increase, the production of warm oceanic crust is high and this
lower-density oceanic crust takes up more space; therefore, occupying more volume of the ocean.
This displaces seawater onto the low-lying portions of the continents.

Question 18

During which period of geologic history did supercontinent Pangaea come into existence? During
which period did it begin to break apart?

Answer 18

The supercontinent Pangaea came into existence at the end of the Paleozoic as the large
continents of Laurasia and Gondwana collided. Pangaea began to break apart about 185 million
years ago during the Jurassic Period.

Question 19

Describe the climate of the present-day American Southwest during the early Jurassic time.

Answer 19

The climate of the early Jurassic Period was likely arid, as evidenced by the many sandstone
formations with dune-related cross-bedding in the American Southwest.

Question 20

Where is most Cretaceous age coal found today in the United States?

Answer 20

Most Cretaceous-age coal is found in western North America due to the widespread formation of
swamps from encroaching shallow seas, similar to the Paleozoic era.

Question 21

Compare and contrast eastern and western America’s geology during the Cenozoic.

Answer 21

Eastern and western North America were very different from one another during the Cenozoic
Era because of their relationship to plate boundaries. The eastern portion of North America was
tectonically stable, allowing for abundant marine sedimentation, especially in the Gulf of Mexico.
The western portion of North America was tectonically active, with the building up of the
southern Rocky Mountains and sediment erosion producing the Great Plains. The Basin and
Range Province also formed during this time, and volcanism began in the northwestern portions
of the continent.

Question 22

What group of organic compounds combine to form proteins and is therefore is necessary for life
as we know it?

Answer 22

Amino acids are the organic compounds essential for the formation of DNA and RNA. Proteins,
made from amino acids, are essential raw materials for life; therefore, amino acids are necessary
for life as we know it

Question 23

What are stromatolites” What group of organisms is thought to have produced them?

Answer 23

Stromatolites are distinctly layered mats composed of the slimy secretions of microscopic
bacteria combined with trapped sediments. These are thought to have been produced by
cyanobacteria, a form of photosynthesizing prokaryote

Question 24

Compare prokaryotes with eukaryote. To which group do all modern multicellular organisms
belong?

Answer 24

Prokaryotes are simple single-celled bacteria that lack nuclei, which means their genetic
material is not separated from the rest of the cell by a nuclear membrane. Eukaryotes are more
advanced organisms with cellular structures that contain nuclei, which separate the genetic
material from the rest of the cell. All multicelled organisms are eukaryotes.

Question 25

What is the Cambrian explosion?

Answer 25

The Cambrian Explosion is the name given to the huge expansion in biodiversity that occurred at
the beginning of the Cambrian period.

Question 26

Describe the obstacles that plants had to overcome in order to inhabit the continents.

Answer 26

To move onto land, the primary difficulty that plants had to overcome was how to obtain water
and stay upright against gravity and winds

Question 27

What group of animals is thought to have moved onto land to become the first amphibians?

Answer 27

Lobe-finned fish were thought to be the first animals to leave the ocean and begin breathing on
land as amphibians.

Question 28

What features of typical amphibians prevent them from living entirely on land?

Answer 28

Amphibians are not true land animals because they are not fully adapted to life completely out of
water. The adults must return to water to lay their eggs. The young are born in water with gills
and tails, and then mature into air-breathing adults

Question 29

What major developments allowed reptiles to move inland?

Answer 29

The development of shell-covered eggs that are laid on land, the formation of evolved lungs, and
a waterproof skin that prevents the loss of body fluids allowed reptiles to move inland. Shell-
covered eggs eliminate the water-dwelling stage of amphibian life, allowing life away from water.

Question 30

What group of plants became the dominant trees during the Mesozoic? Name a modern
descendant of this group.

Answer 30

Gymnosperms, those plants that produce seeds not enclosed in fruits, became dominant in the
Mesozoic. Modern descendants of these gymnosperms include pines, firs, and junipers.

Question 31

What was the dominant reptile group on land during the Mesozoic.

Answer 31

The dominant reptile group on land during the Mesozoic Era was the dinosaurs.

Question 32

What group of reptiles gave rise to modern birds?

Answer 32

The reptile group exemplified by Archaeopteryx had feathered wings and tail, and became the
ancestor of modern birds

Question 33

Identify two groups of reptiles that returned to life in the sea.

Answer 33

Two reptiles that returned to life in the sea were the fish-eating plesiosaurs and ichthyosaurs.
They became efficient swimmers but retained reptilian teeth and lungs.

Question 34

What animal group became the dominant land animals of the Cenozoic era?

Answer 34

In the Cenozoic era, mammals replaced reptiles as the dominant land animal.

Question 35

Explain how the demise of dinosaurs impacted the development of mammals.

Answer 35

Prior to Cenozoic time, mammals were small rodent like creatures that gathered food at night
when dinosaurs were less active. With the demise of the large Mesozoic reptiles, Cenozoic
mammals diversified rapidly due to lack of predation

Question 36

Where did researchers discover most of the evidence for the early evolution of our hominin
ancestors?

Answer 36

Most of the evidence of early evolution of humans has come from Africa, in particular the rift
valley system of East Africa

Question 37

What two characteristics best separate humans from other mammals?

Answer 37

Humans are best separated from other mammals by the presence of a larger brain and bipedal
locomotion utilizing longer legs with hip joints adapted for long-distance walking.

Question 38

Describe one hypothesis that explains the extinction of large mammals in the Pleistocene.

Answer 38

One hypothesis for the extinction of large mammals in the late Pleistocene involves early humans
selectively hunting large animals