12.4 Precambrian History: Formation of Earth's Continents

One important reason we do not know much about the geologic history of the Precambrian is that ________.

• rocks did not exist during much of that time

• the climate was so harsh that erosion removed most of the rocks that formed during the Precambrian

• radioactivity was not measurable during the Precambrian

• we have not yet been able to establish the half-lives for radioactive elements that existed in the Precambrian

• there are very few fossils preserved in Precambrian rocks

Answer explanation

Most (if not all) of the organisms during this long stretch of time were soft bodied marine organisms that would not easily form fossils.

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NGSS.HS-ESS1-6

Zircons found in continental rocks give evidence that continental crust was forming as long ago as ________.

• 4.4 billion years ago

• 1.9 billion years ago

• 564 million years ago

• 70 million years ago

• 10,000 years ago

Answer explanation

Zircons have the capability to survive geologic processes like erosion, transport, even high-grade metamorphism. The oldest minerals found so far are zircons from Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, with an age of 4.404 billion years. This age is interpreted to be the age of crystallization.

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NGSS.HS-ESS1-6

One significant difference between oceanic and continental crust in terms of the long term evolution of Earth's surface is that ________.

• oceanic crust is less dense than continental crust

• oceanic crust preserves a history of ancient deformation better than continental crust

• continental crust is harder to subduct than oceanic crust

• continental crust is more uniform in composition than oceanic crust

• oceanic crust contains more radioactive elements that contribute to the heating of the earth

Answer explanation

Due to their differences in density, continental crust (lower density) does not subduct and therefore is much older than oceanic crust, which gets recycled back into the Earth's mantle through subduction.

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NGSS.HS-ESS1-5

Continental crust is formed by ________.

• melting and differentiation of oceanic crust at subduction zones

• partial melting of mantle rocks

• plumes of hot igneous material that rise from the core-mantle boundary to form hot spots

• the original planetary accretion that also led to the formation of the earth's other layers

• recycling of material in giant lava lakes in the early earth history

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NGSS.HS-ESS2-1

In Rodinia, a well-documented Precambrian supercontinent, ________.

• there is no evidence of North America

• North America was the last collision in the formation of the supercontinent

• North America and South America made up one continuous fragment

• North America was located near the center of the supercontinent

• the Rocky Mountains were located to the south of the North American craton

Answer explanation

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NGSS.HS-ESS1-5

NGSS.HS-ESS2-1

Antarctica became glaciated because ________.

• it moved to a position over the south pole

• ocean circulation changed with the northward movement of South America

• ocean circulation changed with the southward movement of South America

• global climate changed with the formation of the Himalayan Mountains

• a meteorite impact changed the earth's tilt axis

Answer explanation

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NGSS.HS-ESS1-5

NGSS.HS-ESS2-2

NGSS.HS-ESS2-4

Sea level rise can be caused by ________.

• the formation of supercontinents

• rapid erosion from continents that increase the sediment load in the oceans

• fast seafloor spreading

• slow seafloor spreading

• slow erosion from continents that increase the size of land masses and displace water

Answer explanation

New, warm oceanic crust is less dense (take up more space) than cold crust, so fast spreading ridges occupy more volume. As a result, more seawater is displaced, which results in sea level rising. Think of the level of water in a bathtub when you get in.

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NGSS.HS-ESS2-4

NGSS.HS-ESS3-5

Most ________ rocks are devoid of fossils, which hinders correlation of rocks.

• Precambrian

• Paleozoic

• Mesozoic

• Cenozoic

• Mesozoic and Cenozoic

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NGSS.HS-LS4-1

According to your text, which type of body would have looked similar to the photograph below in its early history?

• Earth

• the Moon

• the Sun

• Venus

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NGSS.HS-ESS1-6

The part of the continental crust has attained stability; that is, it has not been affected by significant tectonic activity during the Phanerozoic eon. It consists of the shield and stable platform.

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Vocabulary