Geology Test 3

Question 0

Archean Eon

Answer 0

• Greenstone belts
• First evidence of life
• Chemical evidence

Question 1

Hadean Eon

Answer 1

• Differentiation
• Origin of continental crust

Question 2

Precambrian

Answer 2

Earth’s earliest time is referred
• Corresponding to all time prior to the Cambrian period (which contain conspicuous fossils).
• ~90% of geologic time.
• Rocks have fossils….just inconspicuous.
• Less than 20% of rocks at Earth’s surface are of Precambrian age.
Contains Hadean: 4.6-3.8 billion years ago
• Archean: 3.8-2.5 billion years ago
And Proterozoic eons

Question 3

Hadean eon

Answer 3

In the Precambrian era
earliest interval of geologic time:
• Key points?
• Earth acquired it’s basic configuration
(mantle and crust surrounding the core).
• Insignificant amount of continental crust in
existence.
• Very few rocks of Hadean-Eon age exist today.

Question 4

Archean eon

Answer 4

Second level in the Precambrian
second oldest interval of geologic time:
• Key points?
• First time when substantial continental
crust was formed.
• High heat flow from Earth’s interior was much greater than today….so continents remained small because they were constantly rifting apart.

Question 5

Cratons

Answer 5

Precambrian rock:
large stable interior parts of continents that haven’t undergone substantial tectonic deformation in a long time.
• Edges of continents are sites of active orogeny

Question 6

Precambrian Shield

Answer 6

Precambrian rock:
parts of the craton that are of Precambrian age.
• Canadian Shield is largest; exposed by erosion during recent glaciations
• Mostly Ig/Met; some have Sed rocks providing details about paleo-ecosystems.

Question 7

Hadean Eon

Answer 7

• Early Earth was very hot due to:
• Impacts from asteroids and meteorites
• Radioactive decay
• Initial molten Earth was generally a homogeneously-mixed molten mass.

Question 8

Atmosphere of hadeon eon

Answer 8

• Water vapor
• Hydrogen, carbon monoxide, carbon dioxide, nitrogen
• Methane (CH4) and ammonia (NH3)
• Little oxygen gas (O2)

Question 9

What started first small
continental crust.

Answer 9

A much hotter early Earth melted subducted slabs of basalt to form
magma rich in Na (called granitoid; because richer in Na, not in K). Felsic crust formed by partial melting of oceanic lithosphere.
• Partial melting processes creates felsic magmas.
These felsic granitoids formed the nuclei of it
Tho Don’t have actual continental crustal rocks from Hadean.

Question 10

Greenstone Belts

Answer 10

Part of Archean eon
Rock type
broad regions of elongate, stratified bodies consisting of high-grade metamorphic (felsic) rocks
• Have a distinct green color from metamorphic mineral, chlorite
• Formed by squeezing forearc basin sediments, deformed oceanic crust, and arc volcanics between margins of small protocontinents

Question 11

2 major rock types of Archean eon

Answer 11

Greenstone belts

Banded iron formations

Question 12

Banded Iron Formations (BIF)

Answer 12

• Typical of Archean sedimentary rocks
• Composed of alternations of iron-oxide-rich layers interbedded with chert layers:
• Chert + Fe-rich: precipitated from sea water
• Silica was more concentrated in ocean because this is before diatoms.
• Bacteria may have aided in precipitation of Fe
• The precipitation of iron does not occur in the oceans today.

Question 13

Life first appeared on Earth sometime after…

Answer 13

4.5 Ga

Question 14

Evidence for Archean Life:

Stromatolites

Answer 14

Still created today in association with Cyanobacteria (prokaryotic).
• Earliest known fossil life.

Question 15

Evidence for Archean Life:

Biomarkers

Answer 15

Photosynthesis at 3.7 Ga
• Small carbon particles in deep-water black shales and turbidites
• Carbon is so isotopically light (C12), researchers believe it must be from photosynthesis by an unknown primitive life form (~3.7Ga).

Question 16

Evidence for Archean Life:

oldest fossilized organism

Answer 16

prokaryotic life form found in Archean rock (~ 3.5 Ga).
• Intertwined filaments on pillow lavas
• Similar prokaryotes found today associated with pillow basalts

Question 17

Evidence for Archean Life:

Steranes

Answer 17

compounds produced by eukaryotes
• Discovered in Archean rocks 2.7 Ga BP
• Suggests eukaryotes were present by end of Archean

Question 18

Basis of life

Building blocks of proteins are amino acids. • Amino acids (20) made of:

Answer 18

Carbon
• Hydrogen • Oxygen
• Nitrogen

Question 19

Life on Earth likely originated at:

Answer 19

MOR
No oxidation problem.
• Archean life originated in a warm environment isolated from Earth’s atmospherewarm area adjacent to MOR likely.
• Super-heated water circulating, rising as large vents.
• Known to inhabit these areas today.

Question 20

Today (and probably in the past) these organisms perform:

Answer 20

chemosynthesis.
= harness energy of naturally occurring chemical reactions
They consume the chemical compounds and employ enzymes to speed up the chemical reaction, which release the energy that organisms use for their metabolism.

Question 21

Hadean overview

Answer 21

Earth differentiated
• Moon formed.
• Partial melting of subducted lithosphere when deep Earth was
much hotter lead to development of continental crust.
• High heat rates meant high tectonic plate movements, preventing the formation of large continents.

Question 22

Archean overview

Answer 22

Greenstone belts and BIF
• Larger continents formed as heat dropped within Earth.
• Appearance of life (likely at MOR)
• Oxygen proliferation

Question 23

The fossil record is the basis for the division of the Proterozoic Eon into 3 eras:

Answer 23

3. Neoproterozoic: 1 - 0.54 billion years ago
4. Mesoproterozoic: 1.6 – 1 billion years ago 1. Paleoproterozoic: 2.5 – 1.6 billion years ago

Question 24

Orogen

Answer 24

eroded, deformed remains of what was a mountain (orogenic event).
• Consists of deformed rocks, since leveled by erosion.
• Distinct features (W-E):
Igneous Intrusion Metamorphic belt Fold and thrust belt Undeformed zone

Question 25

Formation of larger cratons began in the late Archean
• Proterozoic: what formed now??

Answer 25

cratons start exhibiting modern-style orogeny • Found in
Canada.

Question 26

Mitochondrion

Answer 26

Site of respiration (energy from food)
• Animal-like protists

Question 27

Chloroplast

Answer 27

Site of photosynthesis
• Animal-like protists – consumed and
retained the cyanobacteria – became
a chloroplast
• First plant-like protists (producer)
evolved from an animal-like protist
(consumer)
• From these two protists: multicellular
animals and plants evolved.