1. Chapter 17 Section 2 Earth’s Early History
Objectives:
-Describe how conditions on early Earth were different from conditions today
-Explain what Miller and Urey’s experiments showed
-State the hypotheses that have been proposed for how life first arose on Earth
-Identify some of the main evolutionary steps in the early evolution of life

2. Key Concept Earth’s Early Atmosphere Contained: Hydrogen Cyanide Carbon Dioxide Carbon Monoxide Nitrogen Hydrogen Sulfide Water

3. The First Organic Molecules
Miller and Urey’s Experiment
Spark simulating
lightning storms
Mixture of gases simulating
atmosphere of early Earth
Condensation
chamber
Water
vapor
Cold water cools chamber, causing droplets to form.
Miller and Urey produced amino acids, which are needed to make proteins, by passing sparks through a mixture of hydrogen, methane, ammonia, and water. This and other experiments suggested how simple compounds found on the early Earth could have combined to form the organic compounds needed for life.
Liquid containing amino acids and other organic
compounds
large organic molecules form tiny bubbles called proteinoid microspheres.
Copyright Pearson Prentice Hall

4. Key Concept
Miller & Urey’s Experiments Suggested: How Mixtures Of The Organic Compounds Necessary For Life Could Have Arisen From Simpler Compounds Present On A Primitive Earth

5. Corrected Experiments Have Produced Cytosine & Uracil
Original Atmospheric Components Not Accurate (Re-Analysis of Chemical Composition of Early Rocks)
Corrected Experiments Have Produced Cytosine & Uracil
Two RNA Bases

6. Copyright Pearson Prentice Hall
The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration
Endosymbiotic Theory
Ancient Prokaryotes
Chloroplast
Plants and plantlike protists
Aerobic
bacteria
Photosynthetic bacteria
Nuclear envelope
evolving
Mitochondrion
Primitive Photosynthetic
Eukaryote
The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. Ancient prokaryotes may have entered primitive eukaryotic cells and remained there as organelles.
Animals, fungi, and
non-plant like protists
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
Copyright Pearson Prentice Hall

8. Origin of Eukaryotic Cells
Lynn Margulis – Boston U. 1960’s
Evidence
Mitochondria & Chloroplasts Contain DNA & Ribosomes Similar To Bacterial DNA & Ribosomes
They Reproduce By Binary Fission

9. Evolution of RNA & DNA Still Unknown However:
RNA Sequences Have Been Found That:
Help DNA Replicate
Transcribe DNA
Translate Proteins
Catalyze Chemical Reactions
Duplicate Themselves
Perhaps RNA Came First

10. Microfossils - 3.5 Billion Years Old
Free Oxygen
Microfossils Billion Years Old
Prokaryotes
Anaerobic (No O2 In Atmosphere)
Photosynthetic Bacteria Arose
2.2 Billion Years Ago
O2 Continuously Released Into The Atmosphere

11. First It Bound Iron In The Oceans
Free Oxygen
First It Bound Iron In The Oceans
Iron Oxides Settled To The Bottom Of The Oceans
Formed Great Bands Of Iron That We Mine Today

12. Next O2 Accumulated In The Atmosphere
Free Oxygen
Next O2 Accumulated In The Atmosphere
O2 Increased
Methane & Hydrogen Sulfide Decreased
Atmosphere Turned Blue

13. First Aerobic Organisms Arise
Free Oxygen
Is Highly Reactive
Deadly To Anaerobes
First Aerobic Organisms Arise

14. Free Oxygen Key Concept
The Rise Of Oxygen In The Atmosphere Drove Some Life Forms To Extinction, While Other Life Forms Evolved New, More Efficient Metabolic Pathways That Used Oxygen For Respiration

15. Variations in CO2 and O2 C = Cambrian O = Ordovician S = Silurian
D = Devonian
C = Carboniferous
P = Permian
Tr= Triassic
J = Jurassic
K = Cretaceous
T = Tertiary
“0” on time scale = Today

16. Sexual Reproduction & Multicellularity
Shortly After Forming Multicellular Organisms Sexual Reproduction Began
A Few Hundred Million Years Later, Multicellular Organisms Arose And Exploded
Accelerated Genetic Variation