Exam 2: Structure and Origins of the Earth

Question 1

What are the layers of the Earth and how do they compare in density?

Answer 1

Inner Core: very dense iron (heavy)
Outer Core: very dense iron (heavy)
Mantle: a mix of iron/silicon (density mix)
Crust: light elements like silicon in crust (light)

Question 2

How was Earth presented at the beginning of time?

Answer 2

Very hostile environment (moon was closer to Earth, lava, meteorites, etc.)

Question 3

_____% of the Earth is iron. (Where is most of this iron in the layers of the Earth?)

Answer 3

35%; most in the core, some in the crust

Question 4

_____% of the Earth is oxygen.

Answer 4

30%

Question 5

Earth is mostly what two things?

Answer 5

Iron and oxygen

Question 6

What is a major part of our crust?

Answer 6

Aluminum

Question 7

When did crust form?

Answer 7

When the molten surface cooled.

Question 8

What evidence suggests that Earth’s crust was once molten (liquid)?

Answer 8

Dense materials would sink if the Earth’s crust was once molten. The evidence of this is that the core (center of the earth) has very dense iron (therefore it sinked). Crust formed when the molten surface cooled.

Question 9

Are there any rocks from the Hadean eon? If not, when in the geologic time scale are the oldest known rocks found?

Answer 9

No; Archean Eon is the earliest time in Earth’s history we have rocks from. (oldest known rocks found in Archean Eon)

Question 10

time when Earth was still molten; oldest eon (earliest time of Earth’s history); a time before rocks

Answer 10

Hadean eon

Question 11

earliest time in Earth’s history we have rocks from

Answer 11

Archean eon

Question 12

What are three reasons why very old rocks are rare (why ancient archean rocks may be hard to find)?

Answer 12

1. Buried under younger rocks
2. Turned into other rocks by melting, metamorphism, or the sediment cycle (weathering, erosion, etc.)
3. Subducted (if oceanic crust; evidence would be subducted back into mantle)

Question 13

What are two ways we identify the oldest rocks?

Answer 13

1. Radiometric dating (isotopes with long half lives)
2. Principles of Stratigraphy (cheaper than radiometric dating)

Question 14

Why are some of North America’s oldest rocks easier to find in Eastern Canada?

Answer 14

Because of weathering and erosion (ex: glaciers have ripped away all the younger rocks that covered these older rocks)

Question 15

Where are the oldest rocks on Earth? They have been dated to be how many years old?

Answer 15

Acasta Gneiss in northern Canada; 4.0 billion years old

Question 16

The oldest known rocks in the solar system are up to _____ billion years old.

Answer 16

4.54 billion years old

Question 17

How old is the oldest rock we’ve found on Earth? Why have older rocks been found elsewhere in the solar system?

Answer 17

4.0 billion years old; because of meteorites

Question 18

What are three reasons why Early Earth is important?

Answer 18

1. NASA Research– chance of life on other planets
2. Understanding changes in Earth’s atmosphere
3. Valuable minerals (iron)

Question 19

iron oxide rocks showing when oxygen levels rose

Answer 19

banded iron formations (BIFs)

Question 20

In what region is a good place to find very old rocks?

Answer 20

Craton and shield regions

Question 21

part of a continent where rocks have not changed since before the Cambrian; include center of US and Canada

Answer 21

Craton

Question 22

Where in North America are very old rocks found?

Answer 22

found in northern geographic areas and mountain ranges.

Question 23

due to weathering and erosion, rocks are not buried. This is part of the craton with Precambrian rocks– but at the surface.

Answer 23

Shield

Question 24

archean and proterozoic rocks

Answer 24

The Canadian Shield

Question 25

T or F: Every continent on Earth has at least one craton region

Answer 25

True

Question 26

What is the percentage of nitrogen, oxygen, and other gasses in the modern atmosphere?

Answer 26

Nitrogen: 78.08%
Oxygen: 20.95%
Other gasses: .97%

Question 27

Oxygen gas in nature is produced by _______ (a connection example of atmosphere and life)

Answer 27

plants

Question 28

energy from sunlight. Plants will take in water and carbon dioxide gas to build a storage battery system out of. When taking in sunlight, they use that energy to break apart oxygen/carbon dioxide to create in a new way. End up with leftover oxygen they don’t need which kicks out into the atmosphere.

Answer 28

photosynthesis

Question 29

Was there oxygen in the Archean? Why or why not?

Answer 29

No because oxygen gas is not produced by non living processes

Question 30

Some minerals only form if oxygen is present, such as ______ ______.

Answer 30

iron oxides

Question 31

Precambrian chemical sedimentary rocks made of iron and oxygen (chert and iron oxide not still forming today)

Answer 31

banded iron formations (BIFs)

Question 32

Irony only dissolves and moves in water if…

Answer 32

there is no oxygen

Question 33

Where is the ONLY place BIFs are found?

Answer 33

Craton and shield regions