Archean Eon Flashcards
Three reasons why there are no rocks older than 4.0 Billion Years Old.
- Due to Metamorphism and Deformation
- Deeply Buried Beneath Younger Rocks
- Contains Few Fossils of any use for Biostratigraphy
Rapidly-rotating, hot, barren, waterless planet, bombarded by meteorites and comets. Wherein there is no continents, intense cosmic radiation, no organisms, and widespread volcanism.
The Precambrian Earth
Five events that summarizes the events of the Archean Eon.
- Differentiation of Earth’s Layers
- Formation of the Atmosphere
- Formation of the Oceans
- Formation of the Continents
- Earth’s Earliest Organisms
Two principal division of the Earth’s surface.
Continents and Ocean Basins
The significant difference between the continents and the ocean basins is called __________.
Relative Levels
remarkably flat features that have the appearance of plateaus protruding above sea level.
Continents
the average depth of the ocean floor is about _______ kilometers
3.8 Kilometres Below Sea Level
The plateaus protruding above sea
level has an average elevation of about _______ kilometer.
0.8 Kilometres
Earth’s first crust was probably composed of ________.
Basalt
The formation of continental crust is simply a continuation
of the ___________ ____________ of Earth materials that
began during the final accretionary stage of our planet.
Gravitational Segregation
Description of Earth’s core.
Metallic
Description of Earth’s Mantle.
Rocky
Description of Earth’s Crust.
Low-Density & Silica-rich
The age of the oldest continental crust is
uncertain, but we can be sure that at least
some was present by ________ billion years ago.
4.0 BYA
Name and Age of the Oldest Mineral Found in Sedimentary Rocks in Australia.
Zircons (ZrSiO₄)
4.4 BYO
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.
False, it should not be defined by such factors.
Defined by the rocks it’s
made of and how it came to be that matter.
Continents
The largest features of the continents can be
grouped into two distinct categories.
Stable Interiors and Mountain Belts
Extensive, flat stable areas that have been eroded nearly to sea level.
Stable Interiors
Uplifted regions of
deformed rocks.
Mountain Belts
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.
Mountain Belts
Expansive, flat regions composed of deformed crystalline rock (metamorphic
rocks).
Shields
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.
Stable Platforms
During the archean eon, hotspot volcanism and the subduction of the oceanic crusts led to the creation of _____________ -_______ __________.
Continent-size Landmasses
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 _________.
Cratons
The portion of a modern craton that is exposed at the surface is referred to as a ________.
Shield
How much of Earth’s exposed Precambrian
crust is Archean?
22%
Locations of the largest exposures of Archean Eon Rocks.
Africa and North America
Rocks that make up the Archean Crust.
Greenstone Belts and Granite-Gneiss Complexes
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.
Granite-Gneiss Complexes
Are subordinate, accounting for only 10% of Archean rocks, and yet they are important in unraveling some of the complexities of Archean tectonic events.
Greenstone Belts
- 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.
Greenstone Belts
Many of the igneous rocks are greenish,
because they contain green minerals such as
chlorite, actinolite, and epidote that formed
during lowgrade metamorphism
Greenstone Belts
Rocks that cooled from ultramafic
lava flows, which are rare in rocks younger than
Archean, and none occur now.
Komatiites
True or False
Thick accumulations of pillow lava are common
in greenstone belts, indicating that much of the
volcanism was subaqueous.
True
Volcanic rock that is composed of forsteritic olivine (Fo90 and upwards), calcic and often chromian pyroxene, anorthite (An85 and upwards) and chromite.
Komatiite
%Silica of Komatiitic Lava
45%
Minimum temperature of Komatiitic Lava.
1600 C
Why is Komatiitic Lava not erupted anymore?
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.
Is theorized to be Earth’s first
supercontinent
Vaalbara
Beginning and Completion Age of Vaalbara
3.6 BYA to 3.1 BYA
When did Vaalbara broke up?
2.5 BYA
The name __________ is derived from the
South African Kaapvaal craton and the West
Australian Pilbara craton.
Vaalbara
The supercontinent that formed approx. 3.0 BYA. It’s name is derived from German language, meaning “Original” or “Fountainhead”.
Ur
Areas of the supercontinent Ur are now parts of which countries?
Australia, Africa (Madagascar), and India
True or False
The supercontinent Ur’s dimernsions are bigger than the modern-day Australia.
False, it is significantly smaller.
True or False
Vaalbara is 500,000 Million Years Older than Ur.
True
True or False
Ur is the successor and/or a continuation of Vaalbara.
False, it is not a continuation nor a successor of Vaalbara.
The supercontinent that is believed to have formed during the Neoarchean Era 2.7 Billion Years Ago.
Kenorland
What caused the formation of Kenorland?
Accretion of Neoarchean Cratons and the Formation of Newer Continental Crusts
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.
True
Causes of reconstructions for Earth’s Supercontinents.
- Swarms of Volcanic Dikes and their Respective Paleomagnetic Orientation
- Similar Stratigraphic Sequences
What is the name of the modern-day core of Kenorland?
Baltic/Fennoscandian Shield
Age of the Baltic/Fennoscandian Shield?
3.1 BYO
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.
Yilgarn Craton
Oldest evidence of life.
Stromatolites
Age of the oldest known undisputed stromatolites that were found in Barberton Greenstone Belt in South Africa.
3.0 Billion Years Old
In Australia, what is the probable age of the Stromatolites that was discovered in Warrawoona Group?
3.3 to 3.5 Billion Years Old
In Greenland, what is the age determined by a chemical evidence in rocks that hosts Stromatolites?
3.8 Billion Years Old
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.
Isua Supracrustal Belts (ISB)
