Name: Date:Biology 11E: Evolution, The History of Life on Earth

(Chapter 25)

Big Ideas:Big Idea Chapters Illustrative Examples

1. The process of evolution drives the diversity and unity of life.1.a.1 Natural selection is a major mechanism of evolution

22.2, 23.2 • Graphical analysis of allele frequencies in a population • Application of the Hardy-Weinberg equilibrium equation

1.a.2 Natural selection acts on phenotypic variations in populations

23.1, 23.4 • Flowering time in relation to global climate change• Peppered moth• Sickle-Cell Anemia• DDT resistance in insects• Artificial selection• Loss of genetic diversity within a crop species• Overuse of antibiotics

1.a.3 Evolutionary change is also driven by random processes

23.3

1.a.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics

22.3, 25.2 • Graphical analysis of allele frequencies in a population • Analysis of sequence data sets • Analysis of phylogenetic trees• Construction of pylogenetic trees based on sequence data

1.b.1: Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.

25.1, 25.3 • Cytoskeleton (a network of structural proteins that facilitate cell movement, morphological integrity and organelle transport) • Membrane-bound organelles (mitochondria and/or chloroplasts) • Linear chromosomes•Endomembrane systems, including the nuclear envelope

1.b.2: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary histories can be tested.

26.1, 26.2, 26.3 • Number of heart chambers in animals• Opposable thumbs• Absence of legs in some sea mammals

Big Idea Big Idea Big Idea1. The process of evolution drives the diversity and unity of life.1.c.1: Speciation and extinction have occurred throughout the Earth’s history,

24.3, 24.4, 25.4 • Five major extinctions • Human impact on ecosystems and species extinction rates

1.c.2: Speciation may occur when two populations become reproductively isolated from each other.

24.1

1.c.3: Populations of organisms continue to evolve.

24.2 • Chemical resistance• Emergent diseases• Observed directional phenotypic change in a population• A eukaryotic example that describes evolution of a structure or process such as heart chambers, limbs, the brain and the immune system.

1.d.1: There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence

4.1, 25.1, 25.3

1.d.2 Scientific evidence from many different disciplines supports models of the origin of life.

26.6

Evolution: The History of Life on Earth

Text Chapter: 24Purpose: To investigate the conditions on early Earth that made life possible and to explore the key events in life’s history .

Early Earth ConditionsThe earliest fossil evidence for life on Earth dates to 3.5 bya. What we know about the origins of life before then is based on modern chemistry, geology and physics observations and experiments.

Scientists hypothesized that four chemical and physical processes could have occurred in conjunction with natural selection to produce simple cells:

1. Abiotic synthesis of small organic molecules (amino acids, nitrogenous bases).2. Joining of small organic molecules into macromolecules (proteins, nucleic acids).3. Packaging of macromolecules into protocells (internal chemistry different from the environment).4. Origin of self-replicating molecules necessary for inheritance.

*Try Investigation: How Did Life Begin on Early Earth. Use the table below to help you complete the table.

Molecules Glycolysis Citric Acid Cycle Cell CycleAcetaldehyde X

Aminobutryic Acid XAminoisobutyric Acid X

Lactic Acid XMethyalanine X

Sarcosine XAlanine XGlycine X

Glutamic Acid XAspartic Acid XAcetic Acid X

Succininc Acid XProprionic Acid X

Fatty Acids XPolypeptides XGlycerides X

Nucleic Acids X

Synthesis of Organic Compounds on Early Earth

Early Earth was a violent place:

-Huge chunks of rocks and ice left over from the solar system’s formation were

constantly slamming into it and generating enough heat to vaporize any available

water, preventing the seas from condensing until

3.8bya.

-Volcanic eruptions also spewed various

noxious chemicals.

What type of chemical do you expect to be present in

Earth’s early atmosphere?

Water vapour, nitrogen, carbon dioxide, methane,

ammonia, hydrogen and hydrogen sulfide.

What molecule common today do you expect to be

missing? Oxygen

Oparin (Russian) and Haldane (British) suggested

during the 1920s that early Earth’s atmosphere was

reducing (electron-adding) and would have allowed

organic compounds to form from simpler molecules.

What energy sources did they hypothesize assisted in the

creation of the first organic molecules?

Lightning and UV Radiation (no ozone to protect Earth)

What have some other suggestions been for the formation of

organic monomers?

-Meteorites, deep see vents/submerged volcanoes.

Abiotic Synthesis of Macromolecules

Life cannot exist just in the presence of monomers, as important proteins and processes require

polymers (macromolecules). Could these have existed on early Earth?

-Yes, simple monomers will form RNA spontaneously and RNA nucleotides will form polymers

if dropped on hot sand, clay or rocks.

-RNA polymer important as can act as catalyst for simple chemical reactions.

Protocells

What benefit would a membrane bound

environment provide for early life on Earth?

-Separate chemical environment containing

necessary organic molecules for chemical

reactions.

Is there any evidence that protocells could have

existed in Early Earth?

-Yes, vesicles form spontaneously when lipids are added to water (creates lipid bilayer).

-Vesicle assembly increased by product of volcanic ash weathering: montmorillonite (a clay).

-Vesicles can divide, increase in size, have a selectively permeable membrance, etc.

Self-Replicating RNA and the Dawn of Natural Selection

RNA was likely the first genetic material. Why is this significant to the development of life on

Earth?

-RNA can also act as enzymes (ribozymes), are involved in protein assembly and can make short

copies of RNA segments.

RNA molecules are single stranded and can take a variety of shapes depending on their

nucleotide sequence. This three dimensional shape can be termed its phenotype.

How could the phenotype of RNA molecules permit their

evolution through natural selection?

-Phenotypes can be affected by environmental conditions,

with the best adapted ones surviving to replicate/reproduce

at a higher frequency.

Would a protocell containing RNA have an advantage over

protocells that did not?

-Yes, RNA is self-replicating, catalytic, etc.

-Important as cells with variation are created and can be acted on by natural selection.

If RNA is so great, why is DNA the dominant genetic material of living things today?

-DNA is more stable because it is double stranded and can be replicated more accurately =

genetic continuity between generations.

The Fossil Record

Evidence of the life forms that have occupied Earth is preserved in layers of sedimentary rock as

fossils.

Does the fossil record provide a complete view of the evolution of life?

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Fortunately, we can determine the relative and absolute date at which fossils were created,

thereby allowing us to piece together the sequence and timeline of life’s evolution.

Key Events in Earth’s History

The study of fossils has allowed scientists to create a

history of life and determine when crucial events occurred.

Familiarize yourself with Table 25.1. It is important that you understand how the geologic

record is divided into categories based on the type of life that inhabited Earth for specific time

periods.

What happens at the end of almost every era and the start of the subsequent era? Are these

events related?

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Some important events are:

First Single Celled Organisms

Why are the rock-like stromatolites in the picture significant to life

on Earth?

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Photosynthesis and Oxygen

Through what process did cyanobacteria first generate oxygen?

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How do we know when oxygen first began to be produced?

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What was the impact of oxygen production on early life forms?

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First Eukaryotes

Eukaryotic cells evolved after prokaryotes around 2.1 bya. How were they different from their

predecessors?

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Below is the Endosymbiont Theory, which hypothesizes how eukaryotes evolved from

prokaryotes.

What evidence do mitochondria and plastids provide to support the Endosymbiont Theory?

1. Inner membranes mitochondria and plastids have enzymes/transport systems homologous to

those found in modern prokaryote membranes.

2. Contain circular DNA with no histone associations.

3. Replicate in a similar way to prokaryotes.

4. Have mechanisms to translate their DNA into protein (as free living

prokaryotes do).

5. Their ribosomes are more similar to prokaryotic ribosomes.

Multicellular Organisms

The first multi-cellular eukaryotes developed 1.5 bya, but were

relatively small until 575 mya. Why was this?

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The first multicellular eukaryotes were colonial. What does this mean?

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Cambrian Explosion

Why is the Cambrian Explosion a significant event in the

history of life on Earth?

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Colonization of Land

The first plants and animals began colonizing land around 500 mya. What characteristics did

they have that allowed them to make the move to terrestrial habitats?

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When did humans diverge from other hominids? When did the human species finally make their

appearance on Earth?

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Extinctions

Why do biologists need to consider the movement of

Earth’s tectonic plates when considering the evolution

of life?

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Mass Extinction and Adaptive Radiation

There are been five major extinctions in the history of Earth and each

has been followed by large increases of life forms (adaptive radiation).

In what other scenarios have adaptive radiations occurred?

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*It is important to remember that evolution is not goal

oriented, but rather is a product of three inter-related

characteristics:

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