Chapter 22 – The Precambrian Earth The Precambrian covers almost 90% of the entire history of the Earth.  Chapter 22 – The Precambrian Earth Produced by S. Koziol 11-26-2014

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.

Zircon Zircon 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/

Asteroid Asteroid are metallic or silica-rich objects that orbit the Sun between the orbits of Mars and Jupiter.

Meteorite Meteorite is a meteor that has fallen to and reached the surface of Earth.

Why do scientists consider the age of meteorites when they try 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 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.  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 crust Earth’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 Both are early Earth Continents. Laurentia Laurentia was an ancient continent that formed the core of modern-day North America. A microcontinent is a small piece of continental crust Laurentia, also called the North American craton

The craton The 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

Laurentia Laurentia - Ancient continent that contained core of modern-day North America

Precambrian shield Precambrian 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 shield Canadian shield - The Precambrian shield in North America.

Precambrian vs. Canadian These are the nuclear (beginning) area of Precambrian rocks present in each of the continents. Precambrian Canadian A Precambrian shield is a continental core of Archean and Proterozoic rock. Canadian Shield is the Precambrian shield specifically of North America.

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.

Outgassing The process by which volcanoes vent water vapor, carbon dioxide, nitrogen, and other substances is called outgassing.

Cyanobacteria are tiny, threadlike photosynthetic organisms.

Stromatolite Stromatolite is a mat or mound composed of billions of cyanobacteria.

Cyanobacteria Cyanobacteria use the process of photosynthesis to produce energy, and oxygen is given off as a waste product.

Stromatolites The 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 bed Red 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) Red bed 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. A 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 acids amino acids - Building blocks of proteins

During the Archean Miller 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 Archean Amino 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 organisms Single-celled organisms that belong to the Kingdom Monera are prokaryotes.

Prokaryote An organism composed of a single cell that does not contain a nucleus and is the simplest kind of cell is a prokaryote.

Eukaryote vs. Prokaryote They both: have DNA as their genetic material membrane bound have ribosomes basic metabolism amazingly diverse in forms Prokaryote Eukaryote A prokaryote is a simple organism composed of a single cell, which does not contain a nucleus, while 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 fauna Ediacaran fauna are fossils of soft-bodied Proterozoic organisms

Varangian glaciation Varangian 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.