evidence of evolution chapter 17. impacts, issues measuring time evidence of events that happened...
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Evidence of Evolution
Chapter 17
Impacts, IssuesMeasuring Time
Evidence of events that happened millions of years ago – such as meteor impacts – lead to inferences about evolution of life on Earth
17.1 Early Beliefs, Confounding Discoveries
Belief systems are influenced by the extent of our knowledge
Beliefs that are inconsistent with systematic observations of the natural world tend to change over time
Naturalists and Biogeography
Aristotle was one of first naturalists – people who observe life from a scientific perspective
In the late 1800s, Alfred Wallace and others were pioneers in biogeography – the study of patterns in the observation of species
Patterns in Biogeography
Comparative Morphology
Comparative morphologists study body plans and structures among groups of organisms • Some organisms are outwardly similar, but
different internally; others differ outwardly, but have similar internal structures
• Some organisms have vestigial parts with no apparent function
Vestigial Body Parts
Fig. 17-3, p. 261
coccyx
limb bud
Geology
Geologists found identical sequences of rock layers in different parts of the world• Different layers held different fossils – evidence
of earlier forms of life
Cumulative findings from biogeography, comparative morphology, and geology led to new ways of thinking about the natural world
Fossils
17.2 A Flurry of New Theories
By the 1800s, many scholars realized that life on Earth had changed over time, and began to think about what could have caused the changes
New Evidence and Old Beliefs
Catastrophism• Georges Cuvier proposed that many species that
once existed became extinct due to catastrophic geological events unlike those known today
Gradualism• Jean-Baptiste Lamarck proposed that individuals
changed in response to their environment, and passed those changes on to their descendents
Reconsidering Old Beliefs
Theory of uniformity• Lyell’s book, Principles of Geology, proposed that
gradual, repetitive geological processes shaped the Earth over great spans of time
• Lyell’s insights shaped Charles Darwin’s thinking during his five-year voyage on the Beagle
Voyage of the Beagle
Darwin observed unusual fossils and diverse species in a range of habitats
Beagle and The Galapagos Islands
17.1-17.2 Key Concepts Emergence of Evolutionary Thought
Long ago, naturalists started to catalog previously unknown species and think about the global distribution of all species
They discovered similarities and differences among major groups, including those represented as fossils in layers of sedimentary rock
17.3 Darwin and Natural Selection
Darwin’s observations of species in different parts of the world helped him understand a driving force of evolution – natural selection
Old Bones and Armadillos
Darwin observed similarities between fossil glyptodons in Argentina and the armadillo
A Key Insight – Variation in Traits
Darwin’s observations:• Populations can produce more individuals than
their environment can support• Some versions of a trait might enhance an
individual’s ability to survive and reproduce in its particular environment
• Example: Finches in the Galapagos Islands
Finches in the Galapagos Islands
Natural Selection
Natural selection• Differential survival and reproduction among
individuals of a population that vary in details of shared, inherited traits
Adaptive trait• Any trait that enhances an individual’s fitness
(ability to survive and reproduce in a particular environment)
Principles of Natural Selection
Table 17-1, p. 265
Stepped Art
17.4 Great Minds Think Alike
Darwin’s insights into evolution were made possible by contributions of scientists who preceded him
Alfred Wallace independently developed the idea of evolution by natural selection
Alfred Wallace
Wallace drew on his own observations of plant and animal species and proposed that natural selection is a driving force of evolution
17.3-17.4 Key Concepts A Theory Takes Form
Evidence of evolution, or changes in lines of descent, gradually accumulated
Charles Darwin and Alfred Wallace independently developed a theory of natural selection to explain how heritable traits that define each species evolve
17.5 About Fossils
Fossils are remnants or traces of organisms that lived in the past
They give us clues about evolutionary relationships
The fossil record will always be incomplete
Fossils
Fossils• Remains of bones, teeth, shells, seeds, spores,
or other body parts
Trace fossils• Evidence of an organism’s activities (nests, trails,
footprints, burrows, bore holes, eggshells, feces)
Fossils
Fig. 17-9a, p. 267
Fig. 17-9b, p. 267
Fig. 17-9c, p. 267
How Do Fossils Form?
Organisms or traces are covered in sediments or volcanic ash
Inorganic compounds dissolved in water slowly replace minerals in bones and hard tissues
Pressure and mineralization transform remains into rocks
Fossil-Containing Sedimentary Rock
The oldest fossils are usually in the deepest layers of sedimentary rocks
The Fossil Record
The fossil record will never be complete• Geologic events obliterated much of it• Slanted toward species with hard parts, dense
populations, wide distribution, long periods of time• Substantial enough to help reconstruct patterns
and trends in the history of life, and establish some lines of descent (lineages)
17.6 Dating Pieces of the Puzzle
Researchers use predictable radioisotope decay to estimate the age of rocks and fossils
Radiometric dating• Reveals the age of a material by determining its
radioisotope and daughter element content
Radioisotopes
Radioisotope• A form of an element with an unstable nucleus• Decays into atoms of another element
• Example: uranium 238 → lead 206
Half-life• The time it takes for half of a radioisotope’s atoms
to decay into a daughter element
Half-Life
Fig. 17-11, p. 268
newly formed rock
parent isotope
after one half-life
after two half-lives
daughter isotope
newly formed rock
parent isotope
daughter isotope
Fig. 17-11, p. 268
Stepped Art
after one half-life
after two half-lives
Animation: Radioisotope decay
Carbon 14 Dating
Animation: Radiometric dating
17.7 A Whale of a Story
New fossil discoveries are continually filling the gaps in our understanding of the ancient history of many lineages
New Links in the Ancient Lineage of Whales
New Links in the Ancient Lineage of Whales
New Links in the Ancient Lineage of Whales
17.5-17.7 Key Concepts Evidence From Fossils
The fossil record offers physical evidence of past changes in lines of descent
We use the property of radioisotope decay to determine the age of rocks and fossils
17.8 Putting Time into Perspective
Geologic time scale• The chronology of Earth’s history• Measured by radiometric dating and fossils in
similar sequences of sedimentary rock layers around the world
The Geologic Time Scale
Fig. 17-14a, p. 270
Fig. 17-14b, p. 271
Animation: Geologic time scale
17.9 Drifting Continents, Changing Seas
For billions of years, slow movements of Earth’s outer layer and catastrophic events have changed the land, atmosphere, and oceans, with profound effects on the evolution of life
Continental Drift
Continental drift• All continents were once part of a supercontinent
– Pangea – that split and drifted apart• Evidence: Magnetic rocks
Plate tectonics• The mechanisms of continental drift• Plate grow from ridges and sink into trenches
Plate Tectonics
Fig. 17-15, p. 272
trench hot spot ridge trench rift
A B C D
A Plumes of molten rock rupture a tectonic plate at what are called “hot spots.” The Hawaiian Archipelago has been forming this way.
B At oceanic ridges, huge plumes of molten rock welling up from Earth’s interior drive the movement of tectonic plates. New crust spreads laterally as it forms on the surface, forcing adjacent tectonic plates away from the ridge and into trenches elsewhere.
C At trenches, the advancing edge of one plate plows under an adjacent plate and buckles it. The Cascades, Andes, and other great coastal mountain ranges formed this way.
D At rifts, continents rupture in their interior as plates slide apart from each other.
Boundaries of Tectonic Plates
San Andreas Fault
Gondwana
Supercontinents continually form and split, altering habitats and influencing evolution
Gondwana• Ancient supercontinent, older than Pangea • Similar fossils and geologic formations in Africa,
India, South America and Australia
The Drifting Continents
Fig. 17-17, p. 273
A 420 mya B 237 mya C 152 mya D 65.5 mya E 14 mya
Fig. 17-17 (top left), p. 273
Fig. 17-17 (top right), p. 273
17.8-17.9 Key Concepts Evidence From Biogeography
Correlating evolutionary theories with geologic history helps explain the distribution of species, past and present
Animation: Comparative pelvic anatomy
Animation: Continental drift
Animation: Finches of the Galapagos
Animation: Geologic forces
Animation: Plate margins
Animation: The Galapagos Islands
ABC video: Creation vs. Evolution
ABC video: Chickens have a new ancestor
ABC video: Indonesian Earthquake
ABC video: Asteroid Menace
Video: Measuring time