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.