IQ # 2 2.The half-life of carbon-14 is about 5600 years. A fossil with ¼ the normal proportion of C 14 is probably _______ years old. 1.Answer the following.

2.The half-life of carbon-14 is about 5600 years. A fossil with ¼ the normal proportion of C14 is probably _______ years old.

1. Answer the following using the diagram below:

a. a common ancestor for D & Fb. most closely related speciesc. least related speciesd. new species C arises at this

pointe. common ancestor for E & F

BC D

EF3 4

2

1

5

A

Chapter 26The History of Life on Earth

IQ #3 • What is the age of the Earth and when did

prokaryotic and eukaryotic life emerge?• Describe the characteristics of the early planet and

its atmosphere.• How did Miller & Urey test the Oparin-Haldane

hypothesis and what did they learned?• What are the methods used to date fossils and rocks• Describe the evidence for the endosymbiotic theory.• How does continental drift explain the current

distribution of species?

Early conditions on Earth

•Earth = 4.6 billion years old•First life forms appeared ~3.8 billion years

ago

How did life arise?1.Non-living small organic molecules2.Small molecules macromolecules (proteins,

nucleic acids)3.Packaged into protocells/Protobionts

(membrane-containing droplets)4.Self-replicating molecules allow for

inheritance First genetic material most likely RNA First catalysts = ribozymes (RNA)

Three Proposed Models of how macromolecules formed

Pre-Biotic Soup Hypothesis (Oparin & Haldane-independently)

**proposed in 1920’s**

Iron-Sulfur Hypothesis (Hydrothermal vents)

Seeded Meteorite impact

Synthesis of Organic Compounds on Early Earth

•Oparin & Haldane:▫Early atmosphere =

H2O vapor, N2, CO2, H2, H2S methane, ammonia

▫Energy = lightning & UV radiation

▫Conditions favored synthesis of organic compounds - a “primitive soup”

Miller & Urey:(1950’s): (tested primordial soup in lab)water, hydrogen, methane, ammonia all 20 amino acids, nitrogen bases, & ATP, DNA, and RNA were formed

Formation of the first Cells

Began as molecular aggregates (microspheres & protobionts)

Divide often (binary fission) Grow larger in size Maintain a level of homeostasis internally Produce electrical potential across surfaces Absorbs materials from the surface (selective

permeability) Catalytic activity

Protocells & Self-Replicating RNA

Molecular Replication Usually involves DNA, RNA and proteins All can form on clay surfaces Self-replication common with DNA & RNA Which formed first?

DNA or RNA?

Molecular Replication

Most hypothesize that RNA was the first to form. Why?

RNA is a versatile molecule and:– Able to function both as an enzyme &

substrate– Single stranded and easily forms H-bonds– Has catalytic properties– Can direct protein synthesis– Folds on itself and from various shapes

Molecular cooperation led to the first cells controlled by RNA

Oldest fossilized cells widely accepted (2 bya) Layers of Microorganisms & sediment called:

Stromatolites

First cells thought to be anaerobic using glycolysis as its metabolic pathway

Heterotrophs → Photoautotrophs → Aerobes—Euk’s(O2 increases) (endosymbiotic theory)

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

As prokaryotes evolved, they exploited and changed young Earth

• The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria (cyanobacteria) and sediment

• Stromatolites date back 3.5 billion years ago

• Living ones in Shark Bay Australia

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• We humans are, in simple terms, bags of water filled with proteins and prokaryotic bacteria (the bacteria in your body outnumber the cells in your body about 10 to 1). We humans have descended from organisms that adapted to living in a prokaryotic world, and we humans retain (conserved in evolutionary terms) in our mitochondria the cellular machinery to power our cells that we inherited (i.e., endosymbiosis) from the prokaryotes of deep time on earth.

•Sedimentary rock (layers called strata)•Mineralized (hard body structures)•Organic – rare in fossils but found in

amber, frozen, tar pits•Incomplete record – many organisms not

preserved, fossils destroyed, or not yet found

Relative Dating Radiometric Dating

•Uses order of rock strata to determine relative age of fossils

•Measure decay of radioactive isotopes present in layers where fossils are found

•Half-life: # of years for 50% of original sample to decay

• Macroevolution consists of the major changes in the history of life– The fossil record chronicles these changes,

which have helped to devise the geologic time scale

The fossil record chronicles macroevolution

Geologic Time Scale

Eon Era Period Epoch (longest to shortest)

Present Day: Phanerozoic Eon, Cenozoic Era, Quaternary Period, Holocene Epoch

Key Events in Life’s History

O2 accumulates in atmosphere

(2.7 bya)

O2 accumulates in atmosphere

(2.7 bya)

Humans(200,000)Humans(200,000)

Endosymbiont Theory

•Mitochondria & plastids (chloroplasts) formed from small prokaryotes living in larger cells

•Evidence:▫Replication by binary fission▫Single, circular DNA (no histones)▫Ribosomes to make proteins▫Enzymes similar to living prokaryotes▫Two membranes

Evidence for endosymbiosis

•Lab cultured Amoebas became infected with bacterium

•Some died, others thrived and became dependent on the invaders

Pangaea = Supercontinent•Formed 250 mya•Continental drift explains many biogeographic puzzles

Movement of continental plates change geography and climate of Earth Extinctions and speciation

Mass extinctions Diversity of life

•Major periods in Earth’s history end with mass extinctions and new ones begin with adaptive radiations