Download Ch 17: The History of Life

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Ch 17: The History of Life
17.1 The Fossil Record
A. Fossils and Ancient Life
1. Fossils- preserved traces and remains of ancient life.
2. Paleontologists- scientists who collect and study fossils.
3. Fossil record- all information about past life.
4. The fossil record includes information about the structure of organisms, what they ate, what ate them, in
what environment they lived, and the order in which they lived.
5.
The fossil record provides evidence about the history of life on Earth. It also shows how different
groups of organisms, including species, have changed over time.
6. Over 99% of all species that have lived on Earth have become extinct, which means that the species has
died out.
B. How Fossils Form
1. Fossils can be as large as a complete, preserved animals, or as small as a fragment.
2. Most fossils form in sedimentary rock.
3. Sedimentary rock forms when exposure to the elements breaks down existing rock into small particles of
sand, silt, and clay
C. Interpreting Fossil Evidence
1. Paleontologists determine the age of fossils using relative dating or radioactive dating.
2. In relative dating, the age of a fossil is determined by comparing its placement with that of fossils in
other layers of rock.
3. Rock layers form in order by age—the oldest on the bottom, with more recent layers on top.
4. Index fossil- a species that is recognizable and that existed for a short period but had a wide geographic
range.
5. Index fossils are used to compare the relative ages of fossils.
6. Relative dating allows paleontologists to estimate a fossil's age compared with that of other fossils.
D. Radioactive Dating
1. Scientists use radioactive decay to assign an absolute age to rocks.
2. Some elements are radioactive and steadily break down into nonradioactive elements.
3. In radioactive dating, scientists calculate the age of a sample based on the amount of remaining
radioactive isotopes it contains.
a. Carbon-14 begins to decay when an organism dies.
b. Carbon-12 is not radioactive and does not decay.
c. By comparing the amounts of carbon-14 and carbon-12 in a fossil, researchers can determine
when the organism lived.
4. Paleontologists use a scale called the geologic time scale to represent evolutionary time.
5. Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide.
17-2 Earth's Early History
A. Formation of Earth
1. Evidence shows that Earth was not “born” in a single event.
2. Earth is about 4.6 billion years old
3. At first, Earth was very hot
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Earth’s atmosphere probably contained hydrogen cyanide, carbon dioxide, carbon monoxide,
nitrogen, hydrogen sulfide, and water.
5. Ab0out 3.8 billion years ago, Earth’s surface cooled enough for water to remain liquid.
6. Water vapor condensed and rain soaked the surface, forming oceans
B. The First Organic Molecules
Could organic molecules have evolved under conditions on early Earth?
1. In the 1950s, Stanley Miller and Harold Urey tried to answer that question by simulating conditions on
the early Earth in a laboratory setting.
a. They filled a container with water and gases from Earth’s early atmosphere.
b. They passed electric sparks through the mixture to stimulate lightening
c. organic molecules formed
2. Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life
could have arisen from simpler compounds present on a primitive Earth.
C. The Puzzle of Life's Origin
1. Evidence suggests that 200–300 million years after Earth had liquid water, cells similar to modern
bacteria were common.
2. In certain conditions, large organic molecules form tiny bubbles called proteinoid microspheres.
3. Microspheres are not cells, but they have selectively permeable membranes and can store and release
energy.
D. Free Oxygen
1. Microscopic fossils, or microfossils, of unicellular prokaryotic organisms resembling modern bacteria
have been found in rocks over 3.5 billion years old.
2. These first life-forms evolved without oxygen.
3. About 2.2 billion years ago, photosynthetic bacteria began to pump oxygen into the oceans.
4. Next, oxygen gas accumulated in the atmosphere.
What occurred when oxygen was added to Earth's atmosphere?
5. The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved
new, more efficient metabolic pathways that used oxygen for respiration.
E. Origin of Eukaryotic Cells
What hypothesis explains the origin of eukaryotic cells?
1. The endosymbiotic theory proposes that eukaryotic cells arose from living communities formed by
prokaryotic organisms.
2. About 2 billion years ago, prokaryotic cells began evolving internal cell membranes.
3. The result was the ancestor of all eukaryotic cells.
4. According to the endosymbiotic theory, eukaryotic cells formed from a symbiosis among several
different prokaryotes.
5. Prokaryotes that use oxygen to generate energy-rich molecules of ATP evolved into mitochondria.
6. Most prokaryotes reproduce asexually. Asexual reproduction:
a. yields daughter cells that are exact copies of the parent cell.
b. restricts genetic variation to mutations in DNA.
4.
17-4 Patterns of Evolution
A. Macroevolution
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1. Macroevolution refers to large-scale evolutionary patterns and processes that occur over long periods of
time.
2.
Six important topics in macroevolution include extinction, adaptive radiation, convergent evolution,
Coevolution, punctuated equilibrium, and changes in developmental ages.
B. Extinction
1. Extinction- the disappearance, or dying out, of a species
2. Most extinction occurs when a species cannot compete for resources or adapt to changing environments
3. By contrast, mass extinctions may occur from combinations of events, such as volcanoes erupting and
asteroids striking Earth.
B. Adaptive Radiation
1. Adaptive radiation- the process by which a single species or a small group of species evolves into
several different forms that live in different ways.
a. For example, in the adaptive radiation of Darwin's finches, more than a dozen species evolved
from a single species.
3. Adaptive radiations can occur on a much larger scale.
a. The disappearance of dinosaurs then resulted in the adaptive radiation of mammals.
b. Different organisms undergo adaptive radiation in different places or at different times but in
similar environments.
Adaptive Radiation Activity 
- color the group most closely related to
the sirenians blue
- color the group most closely related to
cetaceans yellow
~ What is adaptive radiation?
~ Why are scientists not sure of all the
evolutionary relationships shown in the diagram
above?
~ Which two groups are least closely related to artiodactyls?
C. Convergent Evolution
1. Convergent evolution- a process in which unrelated organisms come to resemble one another because
they have evolved similar adaptations to similar environments
a. EX: penguins and dolphins have similar body shapes
i. They are body streamlined to help them swim through water
ii. However, penguins are birds and dolphins are mammals
2. Analogous structures- structures that look and function similarly but are made up of parts that do not
share a common evolutionary history
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c. A dolphin’s fluke and a fish’s tail fin are analogous structures.
4. Homologous structures- are shared by related species because they have been inherited in some way
from a common ancestor.
a. EX: the bones on the front fins of a whale are homologous to the bones in a human arm and both
are homologous to the bones in a chimpanzee arm. The bones in all of these different body parts
on different animals are basically the same bones, but their sizes are different and they serve
slightly different functions in the animals where they are found.
D. Coevolution
1. Coevolution- the process by which two species evolve in response to changes in each other.
a. EX: some plants have evolved poisons to protect themselves from insects.
i. In response, insects have evolved to protect themselves from the poisons
E. Punctuated Equilibrium
1. Punctuated equilibrium- a pattern of evolutionary change
2. Darwin felt that biological change was slow and steady, an idea known as gradualism.
3. The concept of punctuated equilibrium has generated debate and is still controversial among some
biologists today.
4. Evolution has often proceeded at different rates for different organisms at different times during the
history of life on Earth.
F. Developmental Genes and Body Plans
1. It is suspected that changes in genes for growth and differentiation during embryological development
could produce changes in body shape and size.
2. Small changes in the activity of control genes can affect many other genes to produce large changes in
adult animals.
3. Small changes in the timing of cell differentiation and gene expression can make the difference between
long legs and short ones.
Analyzing Data: Textbook p. 438. Answer questions #1-4 below….
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