The Evolution of the Atmosphere:

4.6 to 1 billion years ago

By

Ms. Holl

Introduction

THREE PARTS:

• PART I: Volcanoes

• PART II: Single-Celled Plants

• Part III: Multi-Celled Plants

Part I

Volcanoes

Part II

Multi-Celled Plants

Formed by colonies cyanobacteria.

At least 3.5 billion years old.

Carbon is stored in stromatolites.

Fact:

Chloroplasts are actually cyanobacteria living in plant cells!

Stromatolites

0.5 to 3.5 billion years ago

Shark Bay, Australia

Stromatolites, colonies of cyanobacteria, are alive in Australia today.

2-3 billion years ago: Little free oxygen

Commonly occur in sedimentary rocks 2-3 billion years old.

Alternating dark bands (containing FeO) and light bands of chert (silica and Fe2O3).

Occur from the deposition of alternately dissolved FeO & chert.

“Bands” occur from fluctuating densities of bacteria in an ocean. When bacteria blossoms, it creates oxygen and thus chert, which falls to the ocean floor. An oxygen depletion allows for FeO.

Banded iron formation

History of Atmospheric Oxygen

From Lunine 1999 based on Kastings (1991)

The presence of FeS2 and UO2 set upper limits because oxygen would have produced other oxides from U and Fe

Red beds

Occur earlier than 2 billion years ago.

Form when iron is weathered out of rock in the presence of oxygen.

Part III

Multi-Celled Plants

Summary• PART I: Volcanoes add carbon dioxide, ammonia,

methane, and water vapour to the atmosphere. • PART II: Single-celled plants begin to photosynthesize

which decreases the amount of carbon dioxide and increases the amount of oxygen in the atmosphere. The oxygen reacts with ammonia from volcanoes to add nitrogen to the atmosphere.

• PART III: Multi-celled plants evolved which adds even more oxygen to the atmosphere. More nitrogen is added as plants decay and are consumed by denitrifying bacteria.

Review Questions

• Millions of years ago, the atmosphere contained the following gases: – Ammonia, carbon dioxide, methane, nitrogen,

oxygen and water vapor.

• Which of these gases has increased?

• Which of these gases has decreased?

Review Questions

• Does photosynthesis increase or decrease the amount of oxygen in the atmosphere?– WHY?

• Does photosynthesis increase or decrease the amount of carbon dioxide in the atmosphere?– WHY?

Review Questions

• How did volcanoes change the atmosphere?

• How did single-celled plants change the atmosphere?

• How do multi-celled plants change the atmosphere?

To think about…

• How is the composition of the atmosphere changing today?

http://rainbow.ldeo.columbia.edu/courses/v1001/7.htmlhttp://www.geol.umd.edu/~kaufman/ppt/chapter3/sld019.htmhttp://www.uta.edu/geology/geol1425earth_system/images/

gaia_chapter_11/ArcheanLandscape.jpghttp://www.uta.edu/geology/geol1425earth_system/1425chap11.html

http://www.geol.umd.edu/~kaufman/ppt/chapter3/sld019.htmhttp://www.exhibits.lsa.umich.edu/Exhibits/Anthropology/Diaramas/Nat.Am./Copper/Copper.html

http://www.novaspace.com/LTD/TUCC/PIX/Atmo.jpeghttp://www2.jpl.nasa.gov/files/images/browse/p46022bc.gif

http://www.gsfc.nasa.gov/gsfc/earth/pictures/pinatubo/atmosphere%20after.jpghttp://commons.wikimedia.org/wiki/Image:Air_composition_pie_chart.JPG

http://www.photolib.noaa.gov/sanctuary/images/big/sanc0001.jpg

Picture SourcesPicture Sources

Information SourcesInformation Sources

• http://www.udayton.edu/~INSS/ThemeEvol/EvolTimeline.HSM.ppt

• http://www.lpl.arizona.edu/undergrad/classes/spring2006/Griffith_102-13/LectureNotes/L36-Evolution-Life.ppt

• http://thurmanscience.tripod.com

• http://www.olduniverse.com/1,2.htm