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Chapter 7: Earth System Evolution

Sections in this Chapter

Chapter Challenge

In this section you will find materials that support the implementation of EarthComm, Chapter 7: Chapter Challenge.

Evolution of the Earth System

Geosphere

The Archaean Eon and Hadean, University of California Museum of Paleontology
Brief overview of Earth’s early formation.

Impact Processes on the Early Earth, University of Vienna
Describes the impact processes that occurred during the period of late heavy bombardment.

Earth’s Formation and its Interior Structure, University of Wisconsin-Madison
Overview of Earth’s formation, including the bombardment by meteoric debris.

Evolution of Continents and Oceans, Indiana University
Overview of the processes that form new crust and consume old crust. Also looks at the evolution and features of continental crust, including shields and platforms.

The Precambrian Era, Michigan State University
Describes the geologic history of Earth, including its formation and the evolution of its early crust.

The Evolution of Continental Crust, University of Washington
Examines the conditions required for the formation of continents. Compares the planets and the extent to which those conditions exist.

The Magnetosphere: Our Shield in Space, NASA
Describes Earth’s magnetic field and its relationship to solar wind.

Fluid Spheres

Origin of the Earth’s Atmosphere, Eastern Illinois University
Describes the compositions of Earth’s atmospheres and how they were produced.

How did Earth’s atmosphere and oceans form?, The University of Michigan
Looks at Earth’s early atmosphere and how it was formed by the release of gases trapped in Earth’s interior.

The Carbon Cycle and Earth’s Climate, Columbia University
Describes the cycling of carbon through the Earth system and the role carbon plays in the weathering of rocks.

Banded Iron Formation, American Museum of Natural History
Examines the formation of banded iron formations.

Biosphere

From Soup to Cells—the Origin of Life, University of California Museum of Paleontology
Looks at the evidence of Earth’s earliest life forms.  Considers where and how life originated.

How did life originate?, University of California Museum of Paleontology
Examines the series of steps that led to the formation of multicellular life forms.

Studying the origin of life, University of California Museum of Paleontology
Considers the role of RNA and DNA in the evolution of living things.

Origins of Life on Earth, University of Chicago
Overview of various theories for how life on Earth originated and evolved to multicellular forms.

Cyanobacteria: Fossil Record, University of California Museum of Paleontology
Examines the formation of stromatolites from cyanobacteria and the fossil evidence they contain of early life forms.

Stromatolites, Carleton College
Overview of stromatolites. Includes several images of different stromatolite forms.

Geologic History, The Virtual Fossil Museum
Looks at the geologic time scale and major events that occurred in different periods.

Geologic Timeline, San Diego Natural History Museum
In-depth descriptions of common life forms present in the subdivisions of geologic time.

Causes of Mass Extinctions, Hooper Virtual Paleontological Museum
Detailed website offering information on the causes of extinctions and possible future events.

Section 1: The Evolution of the Geosphere

Learning Outcomes

  • Analyze and interpret data to determine the distribution and age of Earth’s geologic provinces.
  • Analyze and interpret data to determine the age distribution of the basement rocks of the North American continent.
  • Obtain information about the formation and development of Earth’s geosphere.

Inquiring Further

To learn more about Bowen’s reaction series, visit the following web sites:

Igneous Rocks, USGS
Looks at the formation of igneous rocks, including Bowen’s reaction series and fractional crystallization.   To learn more about ophiolites, visit the following web sites:

Ophiolites, Oregon State University
Describes ophiolites and the plate tectonic processes under which they form. Includes information about the Samail ophiolite in southeastern Oman.

The Ocean Basins, Tulane University
Discusses ophiolites and how they form.   To learn more about the period of heavy bombardment, visit the following web sites:

The Archaen Eon and Hadean, Univ. of California Museum of Paleontology
Brief overview of Earth’s early formation.

Impact Processes on the Early Earth, Univ. of Vienna
Describes the impact processes that occurred during the period of late heavy bombardment.

Asteroid Impacts Once Made the Earth’s Oceans Boil for A Whole Year, Smithsonian Magazine
Describes the violent origins of Earth’s beginning and the possibility of boiling oceans.

Earth’s Formation and its Interior Structure, University of Wisconsin-Madison
Overview of Earth’s formation, including the bombardment by meteoric debris.

Is there any record of meteorite impact in the Archean rocks of North America?, Lunar and Planetary Institute
Examines the role of meteorite impact on crustal evolution.

To learn more about greenstone belts and metal ores, visit the following web sites:

Gold, Volcano World
Examines the occurrence of gold in greenstone belts.

Tectonic Evolution of Greenstone Belts, Estrella Mountain Community College
A video that describes the formation of greenstone belts and ways in which they are significant.  Includes the significant metal deposits including copper, iron, and gold associated with greenstones.

General Resources

To learn more about each topic, visit the following websites:

Crustal Evolution

Age of the Earth, USGS
Explains how scientists have determined the age of Earth.

The Archaean Eon and Hadean, Univ. of California Museum of Paleontology
Brief overview of Earth’s early formation.

Impact Processes on the Early Earth, Univ. of Vienna
Describes the impact processes that occurred during the period of late heavy bombardment.

The Precambrian Era, Michigan State University
Describes the geologic history of Earth, including its formation and the evolution of its early crust.

The Evolution of Continental Crust, University of Washington
Examines the conditions required for the formation of continents. Compares the planets and the extent to which those conditions exist.

Weathering and the Early Rock Cycle

Hadean-Archaen Environment, US National Institute of Health Library of Medicine
Examines the Archean and crustal evolution.  Describes earliest evidence for carbon cycle, running water and weathering and erosion and life.

What is the Rock Cycle, Idaho State University
Looks at the formation, break down, and reformation of rock, including weathering processes.

Development of the Magnetosphere

The Magnetosphere: Our Shield in Space, NASA
Describes Earth’s magnetic field and its relationship to solar wind.

The Earth’s Magnetosphere, NASA
Overview of Earth’s magnetic field and its interaction with solar wind.

The Development of the North American Continent

North America’s Geologic History, Britannica
Lecture notes describe the formation of the North American Continent beginning from Earth’s formation.

Historical Geology of North America, Paleontological Research Institution
Examines North American provinces, their origins, and their development.

The Development of the North American Cordillera

Geologic History of Western US, Paleontological Research Institution
The geologic structure and timing of the development of the western margin of the North American continent.

Section 2: The Evolution of the Fluid Spheres

Learning Outcomes

  • Develop and use a model to explain the release of gases from Earth’s mantle into the atmosphere.
  • Obtain information about how Earth’s fluid spheres formed and have changed through time.

Inquiring Further

To learn more about Earth’s magnetic field and the aurora borealis, visit the following web sites:

Aurora Borealis, NPS
Describes the Aurora Borealis and the conditions under which they occur.

How Auroras Form, NASA Jet Propulsion Lab
A series of links provide more information about Aurora, what causes them, their connection to solar wind, and how they have intrigued people through time.

Auroras, The Exploratorium
Examines the conditions that create auroras.   To learn more about earth’s early atmosphere and greenhouse gases, visit the following web sites:

Continents Played Key Role in Collapse and Regeneration of Earth’s Early Greenhouse Gas, Geologists Say, Stanford
Looks at research that is being conducted to study Earth’s early atmosphere and its greenhouse gases.

Atmospheric Carbon Dioxide Greater 1.4 Billion Years Ago, Virginia Tech
Describes a scientific model that has been used to determine how much greenhouse gas there was in Earth’s ancient atmosphere.

Earth’s Early Atmosphere, Northwestern University
Examines the evolution of Earth’s atmosphere.  Overview of the greenhouse gases in Earth’s early atmosphere and the role these gases played in Earth’s early climate.   To learn more about Io, visit the following web sites:

Io: Overview, NASA
Examines Io, its volcanic activity, and the effect of its orbit around Jupiter.

Jupiter: Moons, NASA
Explains the effects of Jupiter’s gravity on Io’s volcanic activity.

General Resources

To learn more about each topic, visit the following websites:

Gases and Liquids in Mantle Rocks

Volcanic Gases and Their Effects, USGS
Examines the dissolved gases in magma and how they are released into the atmosphere during eruptions.

The Evolution of Earth’s Fluid Spheres

Origin of the Earth’s Atmosphere, Eastern Illinois University
Describes the compositions of Earth’s atmospheres and how they were produced.

How did Earth’s atmosphere and oceans form?, The University of Michigan
Looks at Earth’s early atmosphere and how it was formed by the release of gases trapped in Earth’s interior.

Early Interactions Between the Fluid Spheres and the Young Earth

The Carbon Cycle and Earth’s Climate, Columbia University
Describes the cycling of carbon through the Earth system and the role carbon plays in the weathering of rocks.

Fluid Spheres on Other Planets and Moons

Outgassing of a Lunar Atmosphere, Windows to the Universe
Describes the Moon’s atmosphere and where its gases come from.

How Planet Formation affects an Atmosphere, NASA/esa Hubble
Looks at the processes that determine whether a planet will have an atmosphere or not.

The Lost Atmosphere of Mars, NASA
Describes how solar wind and radiation are responsible for stripping the Martian atmosphere.

The Atmosphere of Venus, Windows to the Universe
Overview of the atmosphere of Venus.

Venus, University of Wisconsin-Madison
Describes the composition and characteristics of the atmosphere of Venus.

Section 3: The Origin of Life on Earth

Learning Outcomes

  • Use a model to evaluate a hypothesis about how life may have originated on Earth.
  • Carry out an investigation that examines the development of compounds necessary for life on Earth.
  • Carry out an investigation that examines the evidence of the oldest forms of life on Earth.
  • Carry out an investigation that compares ancient microscopic organisms with modern ones.

Inquiring Further

To learn more about alternative biochemical pathways for life on Earth, visit the following web sites:

Silicon as a Potential Basis for Living Organisms, Life, NIH
Objectively discusses the possibility of the existence of life based off silicon rather than carbon.

Mono Lake and Mars: The Extremophile Connection, Audubon
Connects the evidence collected at Mono Lake that suggests that Mars may have once supported life.   To learn more about the Pilbara Supergroup and the Barberton Supergroup, visit the following web sites:

The oldest records of photosynthesis, University of California, Santa Barbara
Describes stromatolites from low grade metasedimentary rocks in Western Australia and South Africa (the Pilbara Supergroup of Australia and the Barberton Supergroup of South Africa). 

Earth’s Earliest Biosphere—A Proposal to Develop a Collection of Curated Archean Geologic Reference Materials, Astrobiology
Examines the evidence of Earth’s early biosphere as preserved in the Pilbara Supergroup of Western Australia.

Looking through windows into the earliest history of life on Earth and Mars, David Wacey, Nicola McLoughlin, and Martin Brasier
Provides an overview of life contained in the Pilbara Supergroup, and the Barberton Supergroup.

General Resources

To learn more about each topic, visit the following websites:

Origin of Life

From Soup to Cells—the Origin of Life, University of California Museum of Paleontology
Looks at the evidence of Earth’s earliest life forms.  Considers where and how life originated.

How did life originate?, University of California Museum of Paleontology
Examines the series of steps that led to the formation of multicellular life forms.

Studying the origin of life, University of California Museum of Paleontology
Considers the role of RNA and DNA in the evolution of living things.

Origins of Life – Chemosynthesis, Kenyon College
Examines the chemosynthesis theory for the origin of life on earth. Describes how the very first microscopic life on primitive Earth could have evolved as a result of a series of chemical reactions.

Origins of Life on Earth, University of Chicago
Overview of various theories for how life on Earth originated and evolved to multicellular forms.

Miller/Urey Experiment, NASA
Revisits Stanley L. Miller’s and Harold C. Urey’s scientific investigation into the origin of life.

Evidence of Early Life Forms

Cyanobacteria: Fossil Record, University of California Museum of Paleontology
Examines the formation of stromatolites from cyanobacteria and the fossil evidence they contain of early life forms.

Stromatolites, Carleton College
Overview of stromatolites. Includes several images of different stromatolite forms.

Stromatolites of Shark Bay, Government of Western Australia, Department of Environment and Conservation
Examines the diverse and abundant examples of living marine stromatolites found at Shark Bay in Australia.

Section 4: The Biosphere and the Evolution of the Atmosphere

Learning Outcomes

  • Carry out an investigation to explain how iron reacts with oxygen in a solution.
  • Carry out an investigation that examines the evidence for the iron-oxidizing conditions of Earth’s early oceans.
  • Analyze and interpret data to explain changes in the volume of oxygen dissolved in the global ocean over time.
  • Obtain and evaluate information about the role of early life forms in the evolution of the atmosphere.

Inquiring Further

To learn more about banded iron formations, visit the following web sites:

Banded Iron Formation, Sandatlas
Overview of both Superior type and Algoma type banded iron formations.

Algoma-type banded-iron formation deposit, Britannica
Contains a section on banded iron formations and the differences between Superior type and Algoma type.   To learn more about mining the banded iron formations and processing iron ore, visit the following web sites:

Iron Ores, Mining Artifacts and History
Describes the geology and distribution of different iron deposits.

Iron Mining: Where and Why?, Michigan State University
History of iron discovery and production in Michigan.

The Lake Superior Iron Ranges: Geology and Mining, USGS
Overview of the discovery, shipping, and processing of iron ore from the Lake Superior region.

The Steel Making Industry: Raw Materials, World Steel Association
A look at how iron ore is processed into steel.

To learn more about the great oxygenation event, visit the following web sites:

Changes to Earth’s Atmosphere, BBC
A video that looks at how Earth’ atmosphere has changed over its history.

Geologists revisit the Great Oxygenation Event, Washington University in Saint Louis
Examines the rise of oxygen in Earth’s atmosphere and its effects on life.

General Resources

To learn more about each topic, visit the following websites:

Banded Iron Formations

Paleoproterozoic Banded Iron Formation of the Quadrilátero Ferrífero, International Commission on Geoheritage
Examines an area known for and preserved due to its banded iron formations.

Banded Iron Formation, American Museum of Natural History
Exhibit of a 3 billion year old BiF from Canada showing magnetite and silica rich layers.

The Rise of Oxygen in the Atmosphere

Origin of the Earth’s Atmosphere, Eastern Illinois University
Examines the evolution of Earth’s atmosphere and supporting evidence.

Section 5: Geologic Time

Learning Outcomes

  • Develop a model of geologic time using a number of major events in Earth’s history.
  • Carry out an investigation to explore the geologic time scale and the use of the biosphere to divide geologic time.
  • Use a model to explain how radioactive decay can be used to determine the age of a rock.

Inquiring Further

To learn more about the development of the geologic time scale, visit the following web sites:

The Geologic Time Scale in Historical Perspective, University of California Museum of Paleontology
Provides a basic history of the contributions made to the geologic time scale.

Geologic Time Chart History, Idaho Museum of Natural History
Explains how the geologic time scale was not developed in sequential order, but as early geologists identified the layers of rock and the fossils captured within them.   To learn more about how scientists find the absolute ages of rocks, visit the following web sites:

Geochronology, USGS
Provides an overview of selected methods used by USGS scientists for dating and determining the time sequence of events in the rock record.

Absolute Age, Brooklyn College
Describes methods for making quantitative estimates of the number of years ago an event occurred.

Geochronology: Methods, USGS
In-depth descriptions of methods for determining the absolute ages of rocks and sediments.

General Resources

To learn more about each topic, visit the following websites:

The Geologic Time Scale

Geologic History, The Virtual Fossil Museum
Looks at the geologic time scale and major events that occurred in different periods.

Geologic Time, USGS
Overview of geologic time, the geologic time scale, and how geologic events are dated.

What is Geologic Time?, National Park Service
Examines subdivisions of geologic time.  Includes time scales that are drawn to scale in order to compare the relative lengths of geologic time divisions.

Geologic Timeline, San Diego Natural History Museum
In-depth descriptions of common life forms present in the subdivisions of geologic time.

Dating Rocks Using Radioactive Decay

Radiometric Time Scale, USGS
Looks at the discovery and research of radioactive decay and describes how the process works.

How do geologists date rocks? Radiometric dating!, USGS
Examines radioactive decay as a technique for determining the age of rocks and geological events and processes.

How Do Geologists Know How Old a Rock Is?, Utah Geological Survey
Looks at relative dating and absolute dating techniques, including radioactive decay.

Physics of Radiometric Dating, Tulane University
Principles of absolute dating techniques using radioactive decay. Includes examples of isotope systems used to date geologic materials.

Section 6: The Fossil Record

Learning Outcomes

  • Use a model that illustrates the fossil-forming process.
  • Carry out an investigation of organisms in your community that are most likely to become preserved in the fossil record.
  • Obtain information about fossil-forming environments.

Inquiring Further

To learn more about taphonomy and forensic science, visit the following web sites:

A Brief Introduction to Taphonomy, Colby College
Provide details on what, how, and why different organisms are fossilized.

Taphonomy, SERC
Overview of the field of taphonomy. Summarizes different taphonomic indicators and their paleoenvironmental implications. 

Forensic Geocience, The Geological Society of London
Describes some of the diverse roles of lab- and field-based geologists in scientific studies with law enforcement, environmental agencies, and humanitarian organizations.

So You Want to Be a Forensic Scientist!, American Academy of Forensic Sciences
Learn about different careers in the forensic sciences.

Young Forensic Scientists Forum (YFSF), American Academy of Forensic Sciences
The Young Forensic Scientists Forum (YFSF) is a group within the American Academy of Forensic Sciences (AAFS) that is dedicated to the education, enrichment and development of emerging forensic scientists.

To learn more about common geological settings for preservation, visit the following web site:

Preservation and Bias in the Fossil Record, University of California at Davis
Looks at why the depositional setting of an organism’s final resting place is an important factor as to whether or not the organism becomes part of the fossil record.

General Resources

To learn more about each topic, visit the following websites:

Food Chains and Food Webs

Food Chains and Webs, University of Michigan
Provides information on the food chain and the complexity of food webs in a lake.

Fossils and Fossilization

How do Fossils Form?, American Geosciences Institute
Examines the different types of fossils and how they form.

Fossils and Rocks, USGS
Provides background information on how studying fossils became an important part of understanding geologic time.

Fossilization, Idaho Museum of Natural History
A hands-on activity on fossilization and taphonomy.

Fossiliferous Rocks

Mazon Creek Fossils, Illinois State Museum
The plants and animals found in concretions recovered from the Francis Creek Shale are some of the most exciting and important fossils that have been found in the state of Illinois. These fossils are known as the Mazon Creek fossils. This exhibit shows some of the more interesting and dramatic types of fossils recovered from these remarkable deposits.

Sedimentary Rock: Fossiliferous Limestone, Q?RIUS Smithsonian Museum of Natural History
An example of a limestone with a mysterious origin. This site can be used to access the Q?RIUS collection browser to explore a wide range of samples.

Section 7: Evolution

Learning Outcomes

  • Use a model to explain how natural selection favors the best adapted organism in a population.
  • Use a model that demonstrates how fossils can be used to determine rates of evolutionary change.
  • Use a model that demonstrates how sequences of fossils can be used to date fossil specimens.

Inquiring Further

To learn more about the Burgess Shale, visit the following web sites:

Burgess Shale, Yoho National Park of Canada, NASA
Provides a satellite image of the Burgess Shale.

Discover the Burgess Shale, The Burgess Shale Geoscience Foundation
Examines the Burgess Shale fossils and their related geology.

The Burgess Shale, University of California Museum of Paleontology
Describes the Cambrian animal fossils of the Burgess Shale.   To learn more about Charles Darwin, visit the following web sites:

Charles Darwin, University of Missouri-Kansas City
Looks at the life of Charles Darwin and how his ideas developed.

Darwin’s Influences, CK-12 Foundation
Background information on scientists who were connected to Charles Darwin.

Darwin, Darwin Online
Contains a large quantity of information, books, letters, journals, and more on Charles Darwin.

To learn more about a modern mass extinction event, visit the following web sites:

Has the Earth’s sixth mass extinction already arrived?,  University of California at Berkley
Examines the modern global mass extinction as the result of climate change and human activities.

Extinction Rates, University of Connecticut
Lecture notes that look at extinction rates and the current human-caused mass extinction event.

Speciation and Mass Extinction, Berkeley University
Overview of mass extinctions and the formation of new species.

Climate Change and Mass Extinction, Smithsonian
Describes the effects climate change on the rate of species loss.

General Resources

To learn more about Evolutionary Change, visit the following websites:

Understanding Evolution, University of California at Berkley
This giant hub provides links to in-depth coverage of the science of evolution.

Fossil Succession, USGS
Explain changes in life forms, as found in the fossil record, in terms of evolution.

15 Evolutionary Gems, Nature Publishing Group
Provides 15 examples that illustrate the breadth, depth and power of evolutionary thinking.

Section 8: North American Biomes

Learning Outcomes

  • Carry out an investigation of the major biomes of North America.
  • Analyze data on a map of North American biomes.
  • Obtain information about the factors that determine the distribution of biomes on Earth.

Investigate

To find scientific information about most common plants and animals in your biome, visit the following web sites:

Exploring the Environment

Biome Summary, Wheeling Jesuit University
Provides a summary table that lists the climate, moisture, vegetation and animal characteristics of major biomes.  More specific information can be found on the following pages from this site:

Biomes of North America, EPA
Provides detailed descriptions of biomes found in North American.

Characteristics of the Earth's Terrestrial Biomes, Dr. Michael Pidwirny, University of British Columbia Okanagan
Provides descriptions of the animals and plants in different biomes.

Inquiring Further

To learn more about herbivores and carnivores, visit the following web site:

Introduction to Biomes, Britannica Kids
Provides an energy pyramid for several different biomes. See the Calorie Pyramid to see the relative amount of calories the carnivores must obtain from the herbivores to survive.

To learn more about Alaskan animal adaptations to climate, visit the following web site:

Animals, Alaska Department of Fish and Game
Find information on animal species that occur in Alaska.

General Resources

To learn more about Climate and Biomes, visit the following websites:

Biomes, Wheeling Jesuit University
Examines biomes and the climates and ecological communities which define them.

Mission Biomes, NASA
Describes the precipitation, vegetation, and location characteristics of Earth’s biomes.

The World’s Biomes, University of California Museum of Paleontology
In-depth descriptions of the animal, plant, and climate features of Earth’s biomes.

Section 9: Mass Extinction

Learning Outcomes

  • Carry out an investigation that examines changes in Earth’s climate and biosphere 65 million years ago.
  • Carry out an investigation that compares the body structures of modern organisms to extinct organisms.
  • Obtain information about how catastrophic events in Earth’s history have resulted in mass extinctions.

Using Technology

Part A: Changes in Climate and Life at the End of the Mesozoic Era

To view information about paleoclimate before and after the Cretaceous-Paleogene boundary, visit the following web sites:

Cretaceous: Tectonics and Paleoclimate, University of California Museum of Paleontology
A description of the paleoclimate in the Late Cretaceous

Late Cretaceous Climate versus Paleocene Climate, Paleomap Project

Compare the following maps:

Paleomap Project, Paleomap Project
Provides climate maps of the past 1,100 million years.

The Paleocene, Encyclopedia Britannica
Describes the climate that dominated at the onset of the Paleocene Epoch.

To view information about organisms living before and after the Cretaceous-Paleogene boundary, visit the following web sites:

Cretaceous Period: Life, University of California Museum of Paleontology
Description of the flora and fauna of the Late Cretaceous.

The End-Cretaceous (K-T) Extinction, Hooper Virtual Paleontology Museum
Describes the species affected by the catastrophic event that resulted in the mass extinction at the K-T boundary.

Paleocene Mammals of the World, Martin Jehle
The first 10 million years of the age of mammals.

Inquiring Further

To learn more about the Mesozoic–Cenozoic boundary event, visit the following web sites:

Speculated Causes of the End-Cretaceous Extinction, Hooper Virtual Paleontological Museum
Examines two popular hypotheses for the Mesozoic–Cenozoic boundary event.

Extinctions, About.com
Provides links to information on mass extinctions, including hypotheses for the Mesozoic–Cenozoic boundary event.   To learn more about other mass-extinction events in Earth’s history, visit the following web sites:

Mass Extinctions of the Phanerozoic, Hooper Virtual Paleontological Museum
Examines the mass extinction events that occurred during the Phanerozoic.

The Big 5 Mass Extinctions, Our World in Data
Summary of big 5 mass extinction events from the Cambrian to the Tertiary.

General Resources

To learn more about each topic, visit the following websites:

The Extinction Event at the End of the Mesozoic

A Blast from the Past, Smithsonian National Museum of Natural History
Looks at the mass extinction at the end the Cretaceous period (at the end of the Mesozoic Era) and the beginning of the Tertiary Period (early Cenozoic Era).

The End-Cretaceous (K-T) Extinction, Hooper Virtual Paleontological Museum
Examines the Mesozoic–Cenozoic mass extinction.

The Causes of Extinction

Mass Extinctions, Hooper Virtual Paleontological Museum
Provides a short discussion about mass extinctions.  

Causes of Mass Extinctions, Dutton Institute
Detailed website offering information on the causes of extinctions and possible future events.

Dust from the Chicxulub Crater Confirms Reason for Dinosaur’s Extinction, Astronomy.com
Article provides useful background on the how the dinosaur doomsday site was discovered.