Lecture 12 History of Life on Earth

Question 1

How has life on Earth changed over time?

Answer 1

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Question 2

How has life on Earth changed over time?

Answer 2

Past organisms were very different from those presently living

–For example, fossils found in the Saharan Desert document the transition of whales from land to sea

Question 3

What is Macroevolution?

Answer 3

Evolutionary patterns on a larger scale
Cumulative effect of many speciation and extinction events
Example: emergence of terrestrial vertebrates
1. series of speciation events,
2. the impact of mass extinctions on biodiversity,
3. origin of key adaptations such as flight

Question 4

5 patterns of macroevolution

Answer 4

– Stasis
– Exaptation
– Mass extinction
– Adaptive radiation
– Coevolution

Question 5

Macroevolution

Answer 5

• Evolutionary patterns on a larger scale
• Cumulative effect of many speciation and extinction events

The fossil record shows macroevolutionary
changes over large time scales, for example:
* the emergence of terrestrial vertebrates
* the impact of mass extinctions
* the origin of key adaptations, such as flight

Question 6

1.Conditions on early Earth (creating molecules)

Answer 6

Chemical and physical processes
could produce simple cells
through 4 stages

1. Abiotic synthesis of small organic
   molecules
2. Joining of these small molecules
   into macromolecules
3. Packaging of molecules into
   protocells, droplets with
   membranes that maintain an
   internal chemistry different from
   the environment
4. Origin of self-replicating
   molecules

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Question 7

How do we know the conditions on the early Earth?

Answer 7

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Question 8

2. The fossil record

Answer 8

• Reveals changes in the history of life on Earth
• Accumulation of fossils in sedimentary rock
  layers, called strata

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Question 9

Fossil records

Answer 9

Analysis:
* Many past organisms were unlike those living today
* Many organisms once common are now extinct
* New groups arose from previously existing ones

Incomplete record
* Few organisms were preserved as fossils
* Many fossils were destroyed by geologic processes
* Only a fraction of fossils have yet been discovered

Question 10

Dating Rocks and Fossils

Answer 10

1. The order of fossils in rock strata tells us the
   sequence in which they were formed
2. We can infer relative ages of fossils using thismethod, but not their actual ages
3. Radiometric dating:determine the age of
   fossils based on the decay of radioactive
   isotopes
4. A radioactive “parent” isotope decays to a
   “daughter” isotope at a characteristic rate
5. Half-life of isotope = time needed for 50% ofthe parent isotope to decay (known value)

Question 11

Radiometric dating

Answer 11

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Question 12

Using Ratio of C-14 to C-12

Answer 12

● Used to date fossils
up to 75,000 yrs old
● C-12 stable; the
amount in the
organism does not
change after its death
● C-14 radioactive;
slowly decays to N-14
after the organism’s
death

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Question 13

The Geologic Record

Answer 13

Divides Earth’s history
into four eons
* Hadean
* Archean
* Proterozoic
* Phanerozoic

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Question 14

3. Key events in life’s history

Answer 14

1. Single-celled prokaryotes (in the ocean)
   Similar to cyanobacteria
2. Oxygen revolution - photosynthesis

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Question 15

Key events in life’s history

Answer 15

1. Single-celled prokaryotes (in the ocean)
   Similar to cyanobacteria
2. Oxygen revolution - photosynthesis
3. The eukaryotic cell

Question 16

How did the eukaryotes
evolve from their
prokaryotic ancestors?

Answer 16

Serial Endosymbiosis

Question 17

Endosymbiosis Event 1

Answer 17

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Question 18

MITOCHONDRIA

Answer 18

prokaryotic cell engulfed
a small cell that would
evolve into an organelle
found in all eukaryotes

Question 19

Endosymbiosis Event 2

Answer 19

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Question 20

PLASTID (like chloroplast)

Answer 20

A photosynthetic
bacteria was then
engulfed by the
heterotroph

Question 21

Evidence supporting Endosymbiosis

Answer 21

1. Inner membranes have enzymes and transport systems
   that are homologous to those found in the plasma
   membranes of living bacteria.
2. Replication: replicate by a splitting process that is similar to that of certain bacteria.
3. DNA circular molecules not associated with histones
4. Ribosomes - RNA sequences, and sensitivity to certain
   antibiotics similar to bacterial ribosomes

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Question 22

Key events in life’s history

Answer 22

1. Single-celled prokaryotes (in the ocean)
   Similar to cyanobacteria
2. Oxygen revolution - photosynthesis
3. The single-celled eukaryotes
4. The multicellular eukaryotic forms
   ● Algae and soft bodied animals
   ● Cambrian explosion - animal phyla appear
   (sponges, cnidarians, molluscs)
5. Colonization of land (plants and fungi)

Question 23

Summary of Key events in life’s history

Answer 23

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Question 24

4. What affects species diversity?

Answer 24

The rise and fall of groups:
* Differences in speciation and extinction rates
* Depends on speciation and extinction rates of its member species
* These changes are affected by processes
○ Plate tectonics
○ Mass extinction
○ Adaptive radiation

Question 25

The Model of Biodiversity (S vs.E)

Answer 25

Speciation vs Extinction

• The arrows indicate the five
  major mass extinction events.
• Biological diversity increased
  vastly since the Cambrian
  period
• Five major mass extinctions
  have occurred in the distant
  past
• Permian period - 96% of all
  species may have perished
• Cretaceous extinction –
  disappearance of dinosaurs

asteroid impact, perhaps causing global forest
fires and obscuring the Sun for months by
throwing particles into the air.

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Question 26

Theory of plate tectonics

Answer 26

● Movements in the mantle cause the plates to
gradually shift in a process called continental drift
● Tectonic plates can drift apart, collide (forming mountains), or slide past each other (causing earthquakes)

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Question 27

Consequence plate tectonics

Answer 27

● Alters habitats in which
organisms live
● Major Climate change
● Allopatric speciation
Species have 2 choices
* Adapt
* Face extinction

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Question 28

Mass Extinctions

Answer 28

Extinct - species that has been permanently lost
* Simultaneous losses of many lineages
* 99% of all species that have ever lived are now extinct

Fossil records: more than 20 mass extinctions
Extinction can be caused by changes to a species’ biotic or abiotic environment

Mass extinctions occur when large numbers of
species rapidly become extinct worldwide

Question 29

How speciation and extinction affect diversity

Answer 29

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Question 30

Big 5 Mass extinctions events

Answer 30

• Triggered by disruptive global change
• Fossil record over the past 500 my - 5 mass extinctions
• More than half of all of marine species became extinct
  in each event

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Question 31

Big 5 Mass extinctions events

Answer 31

• Permian extinction - 252 mya (caused by volcanoes)
• Cretaceous extinction - 66 mya (dinosaur extinct)

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Question 32

A sixth mass extinction is under way?

Answer 32

• The number of species in the world today > than
  it has ever been
• decreasing at an alarming rate due to human
  activities
• 1 /4 of all species may become extinct in the near future

endangered species

Question 33

Endangered species

Answer 33

organism that is threatened by extinction

Question 34

Major causes lead to 6th mass extinction

Answer 34

• Habitat loss,
• Introduced species
• Overharvesting
• Global climate is warming

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Question 35

Adaptive Radiation

Answer 35

Rapid period of evolutionary change where
many new species arise and adapt to different ecological niches
Causes:
* The opening of niches following mass extinctions
* The evolution of novel characteristics that enable
the exploitation of new resources or habitats
* The colonization of new regions with few or weak
competitors

Question 36

Adaptive Radiation - Mammals

Answer 36

• Prior to 66 million years ago, the size and
  diversity of mammals was restricted by predation
  and competition from dinosaurs
• After the extinction of terrestrial dinosaurs,
  mammals underwent an adaptive radiation

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