Chapter 22 – The Precambrian Earth
Produced by S. Koziol
11-26-2014
The Precambrian covers almost 90% of the entire history of the Earth.
22.1 – The Early Earth
Objectives: Describe the evidence used to determine the age of the Earth.
Understand why scientists theorize that the early Earth was hot.
ZirconZircon is a stable mineral that commonly occurs
in granite.
Oldest known mineral
The oldest known mineral on Earth is zircon.
From the Jack Hills region of Australia a 4.375 billion years old ± 6 million years.
http://www.cnn.com/2014/02/24/world/oldest-earth-fragment/
AsteroidAsteroid are metallic or silica-rich objects that
orbit the Sun between the orbits of Mars and Jupiter.
MeteoriteMeteorite is a meteor that has fallen to and
reached the surface of Earth.
Why do scientists consider the age of meteorites when they try Why do scientists consider the age of meteorites when they try to estimate the age of Earth?to estimate the age of Earth?
Most astronomers agree that the solar system, including Earth, formed all at once, and therefore Earth and meteorites should be about the same age.
Earth’s Current Estimated AgeEarth’s Current Estimated Age
4.54 ± 0.05 billion years This age is based on evidence from radiometric
age dating of meteorite material and is consistent with the ages of the oldest-known terrestrial and lunar samples.
Why scientists theorize that the early Earth was hot.Why scientists theorize that the early Earth was hot.
The combined effects of radioactive decay, asteroid and meteorite bombardment and gravitational contraction made for a hot and inhospitable beginning for Earth.
22.2 – Formations of the Crust and Continents
Objectives: Explain the origin of Earth’s crust.Describe the formation of the
Archean and Proterozoic continents.
Earth’s earliest crustEarth’s earliest crust likely formed as a result of
the cooling of the uppermost mantle.
Earth’s crust first formed at least 4.4 billion years ago, just 160 million years after the formation of our solar system.
Microcontinents
MicrocontinentA microcontinent is a small
piece of continental crust
LaurentiaLaurentia was an ancient
continent that formed the core of modern-day North America.
Both are early Earth Continents.
Laurentia, also called the North American craton
The cratonThe buried and exposed parts of a continental
shield together compose the craton, the stable core of a continent.
Laurentia, also called the North American craton
LaurentiaLaurentia - Ancient
continent that contained core of modern-day North America
Precambrian shieldPrecambrian shield is the Continental cores of
Archean and Proterozoic rock
These are the nuclear (beginning) area of Precambrian rocks present in each of the continents.
Canadian shieldCanadian shield - The Precambrian shield in
North America.
Precambrian vs. Canadian
PrecambrianA Precambrian shield is a
continental core of Archean and Proterozoic rock.
CanadianCanadian Shield is the
Precambrian shield specifically of North America.
These are the nuclear (beginning) area of Precambrian rocks present in each of the continents.
22.3 – Formation of the Atmosphere and Oceans
Objectives: Describe the formation of Earth’s atmosphere and oceans.
Identify the origin of oxygen (O2) in the atmosphere.
Explain the evidence that oxygen (O2) existed in the atmosphere during the Proterozoic.
OutgassingThe process by which volcanoes vent water vapor,
carbon dioxide, nitrogen, and other substances is called outgassing.
Cyanobacteriaare tiny, threadlike photosynthetic organisms.
StromatoliteStromatolite is a mat or mound composed of
billions of cyanobacteria.
CyanobacteriaCyanobacteria use the process of
photosynthesis to produce energy, and oxygen is given off as a waste product.
StromatolitesThe ozone layer that filters ultraviolet radiation
originated from oxygen produced by stromatolites.
Why was the earliest atmosphere eventually replaced by oxygen and nitrogen gases and carbon dioxides?
Both helium and hydrogen gas have small masses. Earth’s gravity was not great enough to keep them from escaping into space. Gases with higher masses like carbon and nitrogen are unable to escape Earth’s gravity and eventually replaced the helium and hydrogen.
Banded iron formation (BIFs)Banded iron formation - Deposit consisting of
alternating bands of chert and iron oxide
Red bedRed bed - Sedimentary rocks younger than 1.8
billion years that are colored by the iron oxides in them
Banded iron formation, Karijini National Park, Western Australia
Banded Iron vs. Red Bed
Banded iron (BIFs)A banded iron formation is a
deposit that consists of alternating bands of chert and iron oxides.
Formed underwater and in an oxygen-poor environment.
Red bedA red bed is a rock younger
than 1.8 billion years that is rusty red in color as a result of the presence of iron oxides.
Formed in an oxygen-rich environment.
Red beds were formed on land, and not under the sea as the BIFs were.
22.4 – Early Life on Earth
Objectives: Describe the experimental evidence of how life developed on Earth.
Distinguish between prokaryotes and eukaryotes.
Identify when the first multicellular animals appeared in geological time.
Hydrothermal vent
hydrothermal vent - Hot water vent at volcanic seafloor rift
Amino acidsamino acids - Building blocks of proteins
During the ArcheanMiller and Urey demonstrated that the basic building blocks of
life were most likely present on Earth during the Archean.
Heat, cyanide, and certain clay minerals can cause amino acids to join together in chains.
During the ArcheanAmino acids have been found in the waters of
hydrothermal vents, suggesting that proteins and nucleic acids could have formed there during the Archean.
Does the Miller and Urey’s experiment prove that life originated in such a liquid?
No. The experiment merely demonstrates that some of the molecules found in living things can arise under conditions that may be like those of early Earth.
Single-celled organismsSingle-celled organisms that belong to the
Kingdom Monera are prokaryotes.
ProkaryoteAn organism composed of a single cell that does
not contain a nucleus and is the simplest kind of cell is a prokaryote.
They both: have DNA as their genetic
materialmembrane boundhave ribosomes basic metabolism amazingly diverse in forms
Eukaryote vs. Prokaryote
Prokaryote
A prokaryote is a simple organism composed of a single cell, which does not contain a nucleus, while
Eukaryote
A eukaryote is an organism that is composed of multiple cells, which contain nuclei and are more complex and larger than those of prokaryotes.
Ediacaran faunaEdiacaran fauna are fossils of soft-bodied
Proterozoic organisms
Varangian glaciationVarangian glaciation - Glacial event that
occurred between 700 and 800 million years ago.
Varangian glaciation
Widespread glaciation at end of the Proterozoic
A major extinction of acritarchs occurred near the end of the Proterozoic, in which widespread glaciation may have played a critical role.
Top Related