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Biology Chapter 17. Evolution : The History of Life. More than ______ of all species that have ever lived on Earth have become extinct. 99.9%. 17-1 The Fossil Record. I. Fossils and Ancient Life A. _______________ are scientists who study fossils.

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biology chapter 17

Biology Chapter 17


The History of Life

More than ______ of all species that have

ever lived on Earth have become extinct.


17 1 the fossil record
17-1 The Fossil Record

I. Fossils and Ancient Life

A. _______________ are scientists who study fossils.

B. The fossil record _________ evidence about the history of life on Earth. It also shows how different __________ _____________, including species, have changed over time.



groups of


ii how fossils form
II. How Fossils Form

remains of

the organism

A. For a fossil to form, either the _________ ___________ or some trace of its presence must be preserved.

1. A precise _________________ must be present to form a fossil.

2. The fossil record provides ____________ ____________ about the history of life.

set of conditions






B. Most fossils are formed in ___________ _______.

1. Sedimentary rock forms from the


2. These particles are carried by _________ ___________ into lakes or seas, where they eventually settle to the bottom.

erosion of rock into sand, silt, and clay.


and rivers


dead organisms may also sink to the


  • As layers of sediment build up over time, ________________________________

_______ and become buried.

4. If conditions are right, the ________ may be kept intact and free from decay.

  • The sediment gradually _____________



compresses into



Figure 17-2 Formation of a Fossil

Section 17-1

Water carries small rock particles to lakes and seas.

Dead organisms are buried by layers of sediment, which forms new rock.

The preserved remains may later be discovered and studied.

Go to Section:

iii interpreting fossil evidence
III. Interpreting Fossil Evidence

age of fossils

A. Paleontologists determine the ________ _______ using two techniques:

1.Relative Dating

a. The age of the fossil is determined by ______________________ with that of fossils in other layers of rock.

b. Rock layers __________________ are generally ________ than those below it.

comparing its placement

nearer to the surface



actual age

compare the relative age of fossils

c. Does not determine the ___________ of the rocks or the fossils.

d. Index fossils are used to ____________ ___________________. These fossils must be easily recognized and must have existed for a short period of time.


radioactive decay of

elements in the rocks

2.Radioactive Dating

a. Based on the ___________________ ___________________.

b. Radioactive elements decay, ________ ______, at a steady rate which is measured in a unit called half-life.

c. Half-life: the length of time required for __________________________ in a sample to decay.

or break


half of the radioactive atoms


natural clocks

d. Different radioactive elements have different half-lives and therefore provide ______________ that “tick” at ______________.


Carbon-14: half-life of about ______ ________

Potassium-40 : half-life of about ______ ___________

different rates




billion years


taken up

they are alive


e. Carbon-14 is _________ by living things while ______________. After an organism dies, the __________ in its body begins to decay to form _________ ___, which escapes into the air.

  • Carbon-14 has a relatively ____________,

it is useful only for dating fossils younger than about ____________.



short half-life

60,000 years


not intact

B. Most fossils are __________. Paleontologists must reconstruct an extinct species from a few fossil bits--- remains of bone, a shell, leaves, or pollen.


Compare/Contrast Table

Section 17-1

Comparing Relative and Absolute Dating of Fossils

Relative Dating

Absolute Dating

Can determine

Is performed by


Age of fossil with respect to another rock or fossil (that is, older or younger)

Age of a fossil in years

Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock

Determining the relative amounts of a radioactive isotope and non-radioactive isotope in a specimen

Imprecision and limitations of age data

Difficulty of radio-assay laboratory methods

Go to Section:

iv geologic time scale
IV. Geologic Time Scale


time scale

A. Scientists first developed the _________ _____________ by studying rock layers and index fossils worldwide. As geologists studied the fossil record, they found _______ ________ in the fossil animals and plants

_________________________. These times were used to mark the segments.



at specific layers in the rock



Precambrian and the present

Paleozoic Era

1. Eras: There are __ eras between the ___________________________.

a. ______________

b. ______________ (Age of Dinosaurs)

c. ______________ (Age of Mammals)

2. Periods: Eras are subdivided into ______.

Mesozoic Era

Cenozoic Era


17 2 earth s early history and 17 3 evolution of multicellular life
17-2 Earth’s Early History and 17-3 Evolution of Multicellular Life

4.6 bya.... *___________________

*many sources of energy: volcanic activity, lightening, meteorites

*______________ in atmosphere: water vapor (H20), nitrogen (N2), and carbon dioxide (CO2), with only small amounts of hydrogen (H2) and carbon monoxide. The primitive atmosphere had little, if any, free _______.

no life forms present

poisonous gases


* intense UV (ultraviolet radiation) from sun

* In the presence of so much available energy, the primitive gases may have reacted with one another and produced small organic compounds, such as nucleotides and amino acids.


bacteria evolve and inhabit most


3.5 bya… *geological disturbances have calmed


_____________ (much like the bacteria of today and well adapted)


cyanobacteria evolve

First organisms

2.2 bya.... *____________________ and form mats in shallow seas. ________ ___________ to produce oxygen (02) via ______________



animal life abounds

1 bya.... *algae and other water-borne photosynthetic organisms abound in the seas

* __________________ in the seas with many ______________________ like sponges, jellyfish and worms.

multicellular organisms

Green Algae

Brown Algae

Red Algae

a special note on the evolution of our atmosphere

Oxygen saturation

  • __________________ begins in the seas
  • ____________________________ (electrical storms split atmospheric water molecules releasing a single oxygen)
  • _______________________________ - (here single oxygen and regular oxygen unite to form O3 or ozone)
  • ___________________ stratosphere - ________ _____ most of the ________________. Life on land can now thrive under this protective ______ which begins 12-15 miles above the earth’s surface.

Oxygen moves into atmosphere

Oxygen reaches upper atmosphere

Ozone layer forms in



harmful UV rays


Paleozoic Era

550 mya.... “____________________” - the Cambrian Period records _____________ _______ of life in evolution’s history. Nearly all of the animal groups known today as well as a strange collection of animals that cannot be assigned to any living group of today appeared in a period of about 10 million years. This evidence is not based upon fossils.

the Cambrian Explosion

an unmatched



basing this new finding upon

molecular evidence

550 mya.... “the Cambrian Explosion”

Scientists are ________________________ ________________ of evolution found in the genes drawn from the living species of 16 animal groups. This has allowed scientists to estimate when all animals last shared a common ancestor with other forms of life. Although controversial, this evidence without the fossil “backup” is widely accepted by many scientists in the field today. If this finding holds up, the animal kingdom had __________________ ___________to develop than the fossils reveal.

hundreds of millions of

years longer

410 mya the
410 mya..... the “______________”

age of the fishes

Cartilaginous Fishes: Sharks, Skates and Rays


first land-based amphibians

360 mya...... ________________________ climb onto the land.


primitive reptiles appear

  • 300 mya...... ______________________--the earth is now a large vegetated landmass with open plains, swamps and primitive trees. ____________ flourished in a tropical climate. Invertebrates flourished in the ocean. From these forests and swamps, of the so called “_____________” period, came the organic materials that ultimately formed our___________________.

Large insects


fossil fuels of today


a period of mass extinctions

where perhaps 95% of all life perished

  • 240 mya... _______________________ __________________________________ over a 100,000 year period. This was possibly due to a meteor impact. This occurred at the end of the_____________.

Paleozoic Era



first flowering plants

  • 205 mya..... beginning of the domination of ___________for 120 mya
  • 138 mya..... ____________________ occur on land and the beginnings of tropical rain forests in some areas. The flowering plants spread and ultimately dominated the landscape through a period of 65 million years.

an era of mass extinction that

ended the dinosaurs as well as 75% of all

plant and animal life.

  • 65 mya.....

Meteorite activity is one explanation for this extinction. This occurred at the end of the_______________.

Mesozoic Era


the earliest fossils of



  • 100,000-200,00 years ago.......

__________________ Homo sapiens date to about this time. Homo sapiens means “_________ __________” and modern humans are classified in this species.

17 4 overview



Intense environmental pressure

Similar environments


Small populations

Different environments

Convergent evolution

Punctuated equilibrium

Adaptive radiation



17-4 overview


that are







can undergo

can undergo

can undergo

can undergo

can undergo

Go to Section:

study guide 17 1
Study guide 17-1

1. Paleontologists

2. It is information about past life that is based on fossils.

3. It provides evidence about the history of life on Earth and how different groups of organisms, including species, have changed over time.

4. Extinct

5. False

6. B, D

7. Sediments settle to the bottom of lakes and seas ad bury dead organisms. The weight of upper layers of sediment compresses lower layers into rock and turns the dead organisms into fossils.

8. a) Relative dating b) Radioactive dating

9. A, B, D

10. False

11. True

12. Half-life

13. Radioactive dating

14. They measure the amount of remaining radioactive isotopes it contains. The smaller the amount, the older the sample.

15. False

16. Cenozoic, Mesozoic, Precambrian time, Tertiary, Jurassic, Carboniferous, Silurian, Cambrian

17. C

18. A, B

19. Eras and periods

20. Mesozoic Era

21. Cenozoic Era

study guide 17 2
Study guide 17-2

1. a) Hydrogen Cyanide b) Carbon Dioxide c) Carbon Monoxide d) Nitrogen e) Hydrogen Sulfide f) Water

2. False

3. Spark simulating lightning storms

4. A, B

5. They are tiny bubbles, formed of large organic molecules, that have some characteristics of living cells.

6. False

7. Experiments show that small sequences of RNA could have formed and replicated on their own in the conditions present on early Earth.

8. DNA is a more stable information-storing molecule than RNA.

9. Microfossils

10. A

11. They produced oxygen, which first removed iron from the oceans and then accumulated in the atmosphere.

12. True

13. True

14. The first step was the evolution of internal cell membranes.

15. It proposes that eukaryotic cells arose from living communities formed by several organisms.

16. A,C,D

17. Sexual reproduction shuffles and reshuffles genes in each generation. This increase in genetic variation greatly increases the chances of evolutionary change due to natural selection.

18. False

study guide 17 3
Study Guide 17-3
  • True
  • A,B,C
  • The animals were al soft-bodied
  • Cambrian
  • False
  • A,B,D
  • B
  • C
  • A
  • Devonian
  • Vast swampy forests of giant ferns and other plants that grew during that time formed thick deposits of sediment that changed into coal over million of years.
  • Mass extinction
  • False
  • Triassic, Jurassic, Cretaceous
  • Reptiles
  • Triassic
  • True
  • True
  • Reptiles
  • Their seeds are enclosed in a fruit, which protects the seed and aids in dispersing it to new locations.
  • More than half of all plant and animals groups were wiped out, including all of the dinosaurs.
  • True
  • Mammals
  • They were generally warm and mild.
  • First it cooled, causing a series of ice ages. The, it began to warm again.
  • False
study guide17 4
Study guide17-4
  • Macroevolution
  • a.)extinction b.)Adaptive radiation c.)Convergent evolution d.)Coevolution e.)Punctuated equilibrium f.)changes in developmental genes
  • Possible causes include a huge asteroid striking Earth, many large volcanoes erupting, continents changing position, and sea levels changing.
  • The disappearance of so many species left habitats open. Often, the result was burst of evolution that produced many new species.
  • Adaptive evolution
  • The disappearance of the dinosaurs led to the adaptive radiation of mammals.
  • Convergent evolution
  • B
  • Coevolution
  • Plats have evolved poisons prevent insects from feeding on them. Insects, in turn, have evolved ways of inactivating or eliminating the poisons.
  • gradualism
  • it may occur when a small population becomes isolated or a small group migrates to a new environment. It may also occur following a mass extinction.
  • Punctuated equilibrium
  • True
  • Homologous hox genes establish body plans in animals that have not shared a common ancestor in hundreds of millions of years. In addition, major evolutionary changes may be based on hox genes.
  • True
study guide vocabulary review
Study guide Vocabulary review
  • C
  • D
  • A
  • C
  • B
  • In coevolution, two species evolve in response to changes in each other over time.
  • Convergent evolution refers to the process by which unrelated organisms come to resemble one another as the evolve similar adaptations to similar environments.
  • Mass extinction is the occurrence of many extinctions around the same time.
  • Punctuated equilibrium is a pattern of macroevolution in which long, stable periods are interrupted by brief periods of rapid change.
  • In adaptive radiation, a single species, or a small group of species, evolves into diverse forms that live in different ways.