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.
Biology Chapter 17
The History of Life
More than ______ of all species that have
ever lived on Earth have become extinct.
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.
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.
dead organisms may also sink to the
_______ and become buried.
4. If conditions are right, the ________ may be kept intact and free from decay.
Figure 17-2 Formation of a Fossil
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.
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age of fossils
A. Paleontologists determine the ________ _______ using two techniques:
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
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
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.
half of the radioactive atoms
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 ______ ___________
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.
it is useful only for dating fossils younger than about ____________.
B. Most fossils are __________. Paleontologists must reconstruct an extinct species from a few fossil bits---remains of bone, a shell, leaves, or pollen.
Comparing Relative and Absolute Dating of Fossils
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
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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
1. Eras: There are __ eras between the ___________________________.
b. ______________ (Age of Dinosaurs)
c. ______________ (Age of Mammals)
2. Periods: Eras are subdivided into ______.
*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
* 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)
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.
Oxygen moves into atmosphere
Oxygen reaches upper atmosphere
Ozone layer forms in
harmful UV rays
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
basing this new finding upon
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
age of the fishes
Cartilaginous Fishes: Sharks, Skates and Rays
first land-based amphibians
360 mya...... ________________________ climb onto the land.
primitive reptiles appear
fossil fuels of today
a period of mass extinctions
where perhaps 95% of all life perished
first flowering plants
an era of mass extinction that
ended the dinosaurs as well as 75% of all
plant and animal life.
Meteorite activity is one explanation for this extinction. This occurred at the end of the_______________.
the earliest fossils of
__________________ Homo sapiens date to about this time. Homo sapiens means “_________ __________” and modern humans are classified in this species.
Intense environmental pressure
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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.
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
13. Radioactive dating
14. They measure the amount of remaining radioactive isotopes it contains. The smaller the amount, the older the sample.
16. Cenozoic, Mesozoic, Precambrian time, Tertiary, Jurassic, Carboniferous, Silurian, Cambrian
18. A, B
19. Eras and periods
20. Mesozoic Era
21. Cenozoic Era
1. a) Hydrogen Cyanide b) Carbon Dioxide c) Carbon Monoxide d) Nitrogen e) Hydrogen Sulfide f) Water
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.
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.
11. They produced oxygen, which first removed iron from the oceans and then accumulated in the atmosphere.
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.
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.