AP Biology, Chapter 25 The History of Life on Earth

1. Give examples of macroevolutionary change.
Emergence of terrestrial vertebrates
Impact of mass extinctions on diversity
Origin of key adaptations like flight
2. Describe the four stages of the hypothesis for the origin of life on Earth.
Abiotic synthesis of small organic molecules
Abiotic synthesis of macromolecules
Self-replicating RNAs undergoing natural selection
3. Describe the contributions that A. I. Oparin, J. B. S. Haldane, and Stanley Miller made toward developing a model for the abiotic synthesis of organic molecules.
Oparin and Haldane: conditions on the early Earth favored the formation of small organic molecules
Miller simulated conditions on the early Earth
Water for oceans
H2, NH3, and CH4 for reducing atmosphere
Sparks for lightning
Formed amino acids
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4. Describe alternative scenarios for the origins of organic molecules on Earth.
Not a reducing atmosphere
N2 and CO2
Simulations still show formation of organics
Localized reducing conditions near volcanoes or deep-sea vents
From space in cosmic dust and carbonaceous chondrite meteorites
5. Describe the key properties of protocells in the evolution of the first cells.
Protocells are aggregates of abiotically produced molecules
If enzymes are included they metabolize
Selective permeability
Can discharge membrane potential = excitability
Can absorb materials and split into smaller units
Lack hereditary traits
6. Describe the evidence that suggests that RNA was the first genetic material. Explain the significance of the discovery of ribozymes.
Ribozymes have a variety of catalytic functions; pre-date enzymes
RNA is central to information transfer in cells
RNA can be copied abiotically
7. Describe how natural selection would have worked in an early RNA world.
RNAs with stability and replicability are favored in vivo
Complementary catalytic functions allow groups of RNAs
Quasispecies in hypercycle” could recombine into a single, multi-trait molecule
Covalent linkage with amino acids may have enhanced catalytic function
8. What are the characteristics of species preferentially found in the fossil record.
Widespread near water
Possessed hard shells, skeletons, etc.
9. Distinguish between relative dating and absolute dating.
Relative dating
Older vs. younger
By position in the rock pile
Superposition: deeper, older; shallower, younger
Radiometric dating
In years
Involves measuring isotopes
10. Explain how isotopes can be used in absolute dating.
Assumes we know the starting ratio of isotopes
Assumes changes in the sample are due to radioactive decay alone
Current ratio is measured; half-life used to calculate time
Examples: C-14 (5700 years), U-238 (4.5 billion years)
11. Explain how the racemization of amino acids is used to estimate fossil age.
Mixtures of enantiomers are called racemic mixtures
Organisms use L-amino acids
After death the L-amino acids begin changing to the D- forms
Making assumptions about the rates allows calculation of the age
12. Describe the major events in Earth’s history from its origin up to about 2 billion years ago. In particular, note when Earth first formed, when life first evolved, and what forms of life existed up until about 2 billion years ago.
4.6 billion years ago (bya) Earth forms
3.9 bya conditions suitable for life
3.5 bya oldest fossils
Stromatolites in fossil record match those growing today
= mounds formed of layered biofilms and sediment
2.7 bya oxygen gas appears in large amounts
13. Describe the timing and significance of the evolution of photosynthesis.
3.5 bya (?) non-oxygenic photosynthesis
2.7 bya oxygenic photosynthesis
Accumulating oxygen reacted with iron metal
Banded iron oxide sediments appear 2.7 bya
2.2 bya significant accumulation of atmospheric oxygen
Killed many anaerobes
Made cellular respiration possible
14. Describe the hypothesized origin of the nuclear membrane and the endomembrane system.
Both from infolding of plasma membrane
Nuclear membrane protects and controls DNA
Endomembrane system compartmentalizes differentiated gene products
15. Describe the evidence that supports the theory that mitochondria and plastids evolved by serial endosymbiosis. Explain what living organisms are the likely relatives of the prokaryotes that gave rise to mitochondria and plastids.
Modern endosymbiotic relationships
Similarities between bacteria and mitochondria and chloroplasts
Cell / organelle size
Prokaryote-type membrane components
Replication by binary fission
Single, circular DNA without histones
Similar transcriptional and translational apparatus
Mitochondria most resemble proteobacteria; plastids cyanobacteria
16. Describe the timing of key events in the evolution of the first eukaryotes and later multicellular eukaryotes. Describe the snowball-Earth hypothesis.
2.1 bya oldest definite eukaryote fossils
1.5 bya multicellular eukaryotes by DNA sequence
1.2 bya fossil multicellular algae
575 mya large diverse multicellular fossils
Corresponds to the thawing of snow-ball Earth
17. Critique the textbooks emphasis on a “Cambrian Explosion.”
Most extant major animal groups originates earlier in the Ediacaran
Only Chrodates and Echinoderms first appear in Cambrian
Only extant groups shown; at least as many major forms are now extinct
Cambrian adaptations
Hard parts for predations and protection
Fossilize more easily; bias makes Cambrian seem bigger
18. Describe the timing of key evolutionary adaptations as life colonized land.
1 bya microscopic terrestrial life
500 mya macroscopic terrestrial; waterproofing tissues
19. How are speciation and extinction rates related to evolutionary succession?
Major adaptations allow rapid speciation, low extinction
Replacement adaptations reverse that ratio
20. Describe the process and practical importance of plate tectonics.
Convection moves large section of Earth’s crust
Sea floor is recycled every 200 my
Forms mountains, splits continents causes volcanoes and earthquakes
21. Describe two dramatic chapters in the history of continental drift. Explain how those movements affected biological evolution.
250 million years ago; formation of Pangaea
Once isolated populations became mixed
Habitat changes: less coastline, drier interiors
180 million years ago: break up of Pangaea
Reinstated widespread geographical isolation
Current biogeographical patterns are the result
22. Explain how mass extinctions have occurred and how they affected the evolution of surviving forms.
Permian, 250 million years ago
Massive volcanic eruptions
Release of large amounts of CO2 è warming
Anoxic oceans from reduced mixing
Cretaceous, 65.5 mya
Asteroid impact
Killed dinosaurs
23. Describe the evidence related to the impact hypothesis associated with the Cretaceous extinctions. Describe the hypothesized consequences of such an impact.
Iridium-rich layer on top of the Cretaceous rocks
Chicxulub; large crater of the right age
Dust released blocked sunlight for years; photosynthesis blocked
Minerals released caused acid precipitation
Molten debris rained on North America
24. Is a sixth mass extinction under way?
Caused by habitat destruction and global climate change?
Current extinction rates 100-1000 times background
Way below mass extinction rates
25. Describe the major consequences of mass extinctions.
Snuffs out lineages
Causes major ecological changes by eliminating adaptations
Opens up niches for adaptive radiations
26. Define and exemplify adaptive radiation.
= formation of many species from a common ancestor
Worldwide Adaptive Radiations
Dinosaurs dominated until extinction
Until that time mammals were small and nocturnal
Regional Adaptive Radiations
Migration to new varied environments
Ex.: finches to Galapagos
27. Explain how the evolution of changes in temporal and spatial developmental dynamics can result in evolutionary novelties.
Relatively few genes control timing and proportions
Small genetic alterations can have big effects
Changes in Rate and Timing
Heterochrony: evolution of morphology from modifying relative growth rates in different parts
Paedomorphosis: retention of juvenile characteristics in the adult due
Changes in Spatial Pattern
May involve changes in the expression of homeotic genes in animals
28. Define exaptation and illustrate this concept with an example.
Exaptation involves a new advantageous use for an old trait
Example: originally feathers may have conserved heat/energy
29. Explain why extracting a single evolutionary progression from a fossil record can be misleading.
Lining up fossils out of context implies uninterrupted direct lineage
A series of changes does not imply an ultimate goal
30. Define and illustrate the concept of species selection. Explain why evolutionary trends are not directional.
Successful, long-lived, widespread species speciate more often
The traits of the long-lived, fecund species appear as a trend in the fossil record
Traits making species fecund, like better dispersal, make it look like all the
species traits are important

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