Archean Eon

Question 1

Three reasons why there are no rocks older than 4.0 Billion Years Old.

Answer 1

1. Due to Metamorphism and Deformation
2. Deeply Buried Beneath Younger Rocks
3. Contains Few Fossils of any use for Biostratigraphy

Question 2

Rapidly-rotating, hot, barren, waterless planet, bombarded by meteorites and comets. Wherein there is no continents, intense cosmic radiation, no organisms, and widespread volcanism.

Answer 2

The Precambrian Earth

Question 3

Five events that summarizes the events of the Archean Eon.

Answer 3

1. Differentiation of Earth’s Layers
2. Formation of the Atmosphere
3. Formation of the Oceans
4. Formation of the Continents
5. Earth’s Earliest Organisms

Question 4

Two principal division of the Earth’s surface.

Answer 4

Continents and Ocean Basins

Question 5

The significant difference between the continents and the ocean basins is called __________.

Answer 5

Relative Levels

Question 6

remarkably flat features that have the appearance of plateaus protruding above sea level.

Answer 6

Continents

Question 7

the average depth of the ocean floor is about _______ kilometers

Answer 7

3.8 Kilometres Below Sea Level

Question 8

The plateaus protruding above sea
level has an average elevation of about _______ kilometer.

Answer 8

0.8 Kilometres

Question 9

Earth’s first crust was probably composed of ________.

Answer 9

Basalt

Question 10

The formation of continental crust is simply a continuation
of the ___________ ____________ of Earth materials that
began during the final accretionary stage of our planet.

Answer 10

Gravitational Segregation

Question 11

Description of Earth’s core.

Answer 11

Metallic

Question 12

Description of Earth’s Mantle.

Answer 12

Rocky

Question 13

Description of Earth’s Crust.

Answer 13

Low-Density & Silica-rich

Question 14

The age of the oldest continental crust is
uncertain, but we can be sure that at least
some was present by ________ billion years ago.

Answer 14

4.0 BYA

Question 15

Name and Age of the Oldest Mineral Found in Sedimentary Rocks in Australia.

Answer 15

Zircons (ZrSiO₄)

4.4 BYO

Question 16

True or False

From the geologic perspective, a continent is defined by its size, location, who discovered it, or whether it is surrounded by oceans.

Answer 16

False, it should not be defined by such factors.

Question 17

Defined by the rocks it’s
made of and how it came to be that matter.

Answer 17

Continents

Question 18

The largest features of the continents can be
grouped into two distinct categories.

Answer 18

Stable Interiors and Mountain Belts

Question 19

Extensive, flat stable areas that have been eroded nearly to sea level.

Answer 19

Stable Interiors

Question 20

Uplifted regions of
deformed rocks.

Answer 20

Mountain Belts

Question 21

Tend to be long, narrow features at the margins of continents, and the flat, stable areas are typically located in the
interior of the continents.

Answer 21

Mountain Belts

Question 22

Expansive, flat regions composed of deformed crystalline rock (metamorphic
rocks).

Answer 22

Shields

Question 23

Other flat areas of the
stable interior in which highly deformed rocks,
like those found in the shields, are covered by
a relatively thin veneer of sedimentary rocks.

Answer 23

Stable Platforms

Question 24

During the archean eon, hotspot volcanism and the subduction of the oceanic crusts led to the creation of _____________ -_______ __________.

Answer 24

Continent-size Landmasses

Question 25

Within the deepest regions of these collision zones, partial melting of the thickened crust generated silica-rich magmas that ascended and intruded the rocks above. The result was the formation of large crustal provinces that, in turn, accreted with others to form even larger crustal blocks. These crustal blocks are called _________.

Answer 25

Cratons

Question 26

The portion of a modern craton that is exposed at the surface is referred to as a ________.

Answer 26

Shield

Question 27

How much of Earth’s exposed Precambrian crust is Archean?

Answer 27

22%

Question 28

Locations of the largest exposures of Archean Eon Rocks.

Answer 28

Africa and North America

Question 29

Rocks that make up the Archean Crust.

Answer 29

Greenstone Belts and Granite-Gneiss Complexes

Question 30

complexes are actually composed of a variety of rocks, with granitic gneiss and granitic plutonic rocks being the most common, that were probably derived from plutons emplaced in volcanic island arcs.

Answer 30

Granite-Gneiss Complexes

Question 31

Are subordinate, accounting for only 10% of Archean rocks, and yet they are important in unraveling some of the complexities of Archean tectonic events.

Answer 31

Greenstone Belts

Question 32

- has three main rock association; its lower and middle parts are mostly volcanic, whereas the upper rocks are mostly sedimentary. - typically have a synclinal structure. - measure anywhere from 40 to 250 km wide and 120 to 800 km long.

Answer 32

Greenstone Belts

Question 33

Many of the igneous rocks are greenish, because they contain green minerals such as chlorite, actinolite, and epidote that formed during lowgrade metamorphism

Answer 33

Greenstone Belts

Question 34

Rocks that cooled from ultramafic lava flows, which are rare in rocks younger than Archean, and none occur now.

Answer 34

Komatiites

Question 35

True or False Thick accumulations of pillow lava are common in greenstone belts, indicating that much of the volcanism was subaqueous.

Answer 35

True

Question 36

Volcanic rock that is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian pyroxene, anorthite (An85 and upwards) and chromite.

Answer 36

Komatiite

Question 37

%Silica of Komatiitic Lava

Answer 37

45%

Question 38

Minimum temperature of Komatiitic Lava.

Answer 38

1600 C

Question 39

Why is Komatiitic Lava not erupted anymore?

Answer 39

The Earth was 300 C hotter during the Archean Eon, making it possible to erupt Komatiitic Lava to the surface. Basically, the Earth possessed more radiogenic heat.

Question 40

Is theorized to be Earth's first supercontinent

Answer 40

Vaalbara

Question 41

Beginning and Completion Age of Vaalbara

Answer 41

3.6 BYA to 3.1 BYA

Question 42

When did Vaalbara broke up?

Answer 42

2.5 BYA

Question 43

The name __________ is derived from the South African Kaapvaal craton and the West Australian Pilbara craton.

Answer 43

Vaalbara

Question 44

The supercontinent that formed approx. 3.0 BYA. It’s name is derived from German language, meaning “Original” or “Fountainhead”.

Answer 44

Ur

Question 45

Areas of the supercontinent Ur are now parts of which countries?

Answer 45

Australia, Africa (Madagascar), and India

Question 46

True or False The supercontinent Ur’s dimernsions are bigger than the modern-day Australia.

Answer 46

False, it is significantly smaller.

Question 47

True or False Vaalbara is 500,000 Million Years Older than Ur.

Answer 47

True

Question 48

True or False Ur is the successor and/or a continuation of Vaalbara.

Answer 48

False, it is not a continuation nor a successor of Vaalbara.

Question 49

The supercontinent that is believed to have formed during the Neoarchean Era 2.7 Billion Years Ago.

Answer 49

Kenorland

Question 50

What caused the formation of Kenorland?

Answer 50

Accretion of Neoarchean Cratons and the Formation of Newer Continental Crusts

Question 51

True or False Kenorland comprised of what later became Laurentia, the core of modern-day North America and Greenland, Baltica (modern-day Scandinavia and Baltic), Western Australia, and Kalahari.

Answer 51

True

Question 52

Causes of reconstructions for Earth’s Supercontinents.

Answer 52

1. Swarms of Volcanic Dikes and their Respective Paleomagnetic Orientation 2. Similar Stratigraphic Sequences

Question 53

What is the name of the modern-day core of Kenorland?

Answer 53

Baltic/Fennoscandian Shield

Question 54

Age of the Baltic/Fennoscandian Shield?

Answer 54

3.1 BYO

Question 55

What is the name of the craton whose famous for hosting the oldest known mineral (Zircon crystals that are 4.4 BYO) discovered in present-day Western Australia.

Answer 55

Yilgarn Craton

Question 56

Oldest evidence of life.

Answer 56

Stromatolites

Question 57

Age of the oldest known undisputed stromatolites that were found in Barberton Greenstone Belt in South Africa.

Answer 57

3.0 Billion Years Old

Question 58

In Australia, what is the probable age of the Stromatolites that was discovered in Warrawoona Group?

Answer 58

3.3 to 3.5 Billion Years Old

Question 59

In Greenland, what is the age determined by a chemical evidence in rocks that hosts Stromatolites?

Answer 59

3.8 Billion Years Old

Question 60

The ______ __________ ______ dates to between 3.7 billion and 3.8 billion years old. Scientists have pored over the belt for signs of life, but until now found only indirect evidence—chemical signatures of carbon and sulfur isotopes that might have been the handiwork of microbes.

Answer 60

Isua Supracrustal Belts (ISB)