This document summarizes clues that provide evidence for evolution from the fossil record and comparisons between living things. It discusses how fossils are formed and dated, either relatively based on rock layers or radiometrically using radioactive elements. The fossil record shows that simpler life forms existed earlier and more complex forms appeared later, and sometimes fossils can reveal aspects of ancient organisms' environments and behaviors. Additional evidence comes from homologous and vestigial structures, embryology, and DNA comparisons that indicate evolutionary relationships between species.

1. Chapter 6:
Adaptations over Time
SECTION2: CLUES
ABOUT EVOLUTION
7th Grade Life Science
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2. A. Clues from Fossils
1. Fossils are used as evidence of evolution.
2. Fossils are created when plants/animals die and
become covered with silt and mud.
a. Over millions of years rock forms and the imprint of the
organism is left on the rock.
3. The Green River Formation (textbook pg 163) is on of
the richest fossil deposits in the world.
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3. B. Types of Fossils
1. Most of the evidence for evolution comes from fossils.
2. Most fossils are found in SEDIMENTARY rock.
a. Sedimentary rock is formed when layers of sand, silt, clay, or
mud are compacted and cemented together, or when minerals
are deposited from a solution.
b. Limestone, Sandstone, and Shale are all examples of
sedimentary rocks.
3. Fossils are found more often in limestone than in any
other kind of sedimentary rock.
4. The fossil record provides evidence that living things
have evolved.
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6. C. Determining a Fossils Age
1. Paleontologists are scientists who study the history of
life on Earth.
a. The use clues provided by unique rock layers and the fossils
they contain.
i. Provide info about geology, weather, and life forms that
were present during the geological time period.
2. Two basic methods used:
a. Relative dating and radiometric dating.
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7. 3. Relative Dating
a. Relative dating is based on the idea that in undisturbed
areas, younger rock layers are deposited on top of older
rock layers. (See diagram below)
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8. 3. (Relative Dating continued)
b. Provides only an estimate of a fossils age.
c. Estimate made by comparing the ages of the rock layers
found above and below the fossil layer.
d. Example:
i. A 50 million year old rock layer lies below a fossil, and a 35
million year old layer lies above it; the fossil would then be
between 35 million and 50 million years old.
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9. 4. Radiometric Dating
a. Gives scientists a more accurate reading.
b. Uses a radioactive elements.
c. Process of radiometric dating (Video Clip Next Slide)
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11. D. Fossils and Evolution
1. Fossils provide a record of organisms that live in the
past.
a. Fossil record does have gaps…like missing pages in a book.
b. Gap exists b/c most organisms DO NOT become fossils.
2. Because of fossils, scientists have concluded:
a. Simpler life forms existed earlier.
b. More complex life forms appeared later.
3. Fossils provide indirect evidence that evolution has
occurred on Earth.
4. Fossils can be use to make models that show what the
organism might have looked like.
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12. D. Fossils and Evolution (continued)
5. From fossils scientists can sometimes determine:
a. Whether they lived in groups or alone.
b. What type of food they ate.
c. What kind of environment they lived in.
6. Most fossils represent extinct organisms.
7. From fossil records, scientists have concluded that
more than 99% of all organisms that have ever existed
on Earth are now extinct. WOW!!!!!!
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13. E. More Clues About Evolution
1. Sometimes Evolution can be observed directly without
fossils.
a. Plant breeders observe evolution when they use cross breeding
to produce genetic changes in plants.
b. The development of antibiotic resistance in bacteria is another
example.
c. Entomologists (study insects) have noted similar rapid evolution
of pesticide resistant insect species.
2. Indirect Evidence of Evolution
a. Indirect evidence does not provide proof of evolution, but it does
support the idea that evolution takes place over time.
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14. F. Embryology
1. The study of embryos
and their development
is called embryology.
a. Embryo= earliest growth
stage of an organism.
b. The similarities of Figure
12 suggest and
evolutionary relationship
among all vertebrate
species.
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15. G. Homologous Structures
1. Body parts that are similar in origin and structure are
called homologous.
2. Homologous structures can also be similar in function.
3. They often indicate that two or more species share
common ancestors.
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16. H. Vestigial Structures
1. Vestigial Structures are structures that don’t seem to
have a function.
2. They provide evidence of evolution.
a. Manatees, snakes, and whales no longer have back legs, but
like all animals with legs, they still have pelvic bones.
3. The human appendix is a vestigial structure
a. Appears to be small version of the cecum, which is an important
part of the digestive tract of many mammals.
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17. I. DNA
1. Examination of ancient DNA often provides additional
evidence of how some species evolved from their extinct
ancestors.
2. Scientists can also determine how closely related
organisms are, for example, DNA studies indicate that
dogs are the closest relatives of bears.
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