Transcript Chapter 17 Section 2 Earth’s Early History

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
Key Concept
Earth’s Early Atmosphere Contained:
Hydrogen Cyanide
Carbon Dioxide
Carbon Monoxide
Nitrogen
Hydrogen Sulfide
Water
The First Organic Molecules
• Miller and Urey’s Experiment
Spark simulating
Mixture of gases
simulating
atmosphere of early
Earth
lightning storms
Condensation
chamber
Water
vapor
Cold water cools
chamber, causing
droplets to form.
Liquid containing amino acids and
other organic
compounds
large organic molecules
form tiny bubbles called
proteinoid microspheres.
Copyright Pearson Prentice Hall
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
Original Atmospheric Components
Not Accurate
(Re-Analysis of Chemical Composition of Early Rocks)
Corrected Experiments Have Produced
Cytosine & Uracil
Two RNA Bases
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
Aerobic
bacteria
Nuclear
envelope
evolving
Ancient Anaerobic
Prokaryote
Photosynthetic
bacteria
Plants and
plantlike
protists
Mitochondrion
Primitive Aerobic
Eukaryote
Primitive Photosynthetic
Eukaryote
Animals,
fungi, and
non-plant like
protists
Copyright Pearson Prentice Hall
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
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
Free Oxygen
Microfossils - 3.5 Billion Years Old
–Prokaryotes
–Anaerobic (No O2 In Atmosphere)
–Photosynthetic Bacteria Arose
• 2.2 Billion Years Ago
• O2 Continuously Released Into The
Atmosphere
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
Free Oxygen
Next O2 Accumulated In The Atmosphere
–O2 Increased
–Methane & Hydrogen Sulfide
Decreased
–Atmosphere Turned Blue
Free Oxygen
Is Highly Reactive
Deadly To Anaerobes
First Aerobic Organisms Arise
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
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
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