BIOL 1F90 Study Guide - Midterm Guide: Cambrian Explosion, Igneous Rock, Cambrian
20 Apr 2016
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BIOLOGY MIDTERM EXAM SAMPLE QUESTIONS
CHAPTER 20.2 – HISTORY OF LIFE ON EARTH
1. What is the geological time scale (Order of periods, time periods of existence, mass
extinctions, what organisms survived and how did these organisms adapt)?
Eons
Eras
Periods
History of Life on Earth
Precambrian
Archaean
Early
3.8-3.5 bya – prokaryotic cells first appear
3.5 bya – fossils of primitive cyanobacteria
Late
1.8 bya – eukaryotic cells first appear
Middle
1.5 bya – multicellular eukaryotic organisms first appear
Late
632 mya – first animals appear
590 mya – bilateral invertebrate animals first appear
Phanerozoic
Paleozoic
Cambrian
543 mya – bilateral invertebrate animals first appear
533-525 mya – Cambrian explosion results in diverse
animal life
520 mya – first vertebrates; first land plants
Ordovician
Large glaciers caused water levels to drop (60% marine)
Silurian
440 mya – large terrestrial colonization by plants and
animals
Devonian
400 mya – seed plants first appear; tetrapods and insects
first appear; Extinction of marine species (unknown cause)
Carboniferous
300 mya – reptiles first appear
Permian
Glaciation (water increase)/eruption (climate) (90-95%
marine)
Mesozoic
Triassic
225-200 mya – dinosaurs and mammals first appear
Volcanic eruptions – killed marine/terrestrial life
Jurassic
160 mya – birds first appear
Cretaceous
135 mya – flowering plants first appear
Meteorite (cool surface)/eruption (blocked sun) (K/T
boundary)
Cenozoic
Tertiary
7 mya – hominoids first appear
Quaternary
Homo sapiens appeared 130 000 years ago
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a. Where do the prokaryotic organisms and the eukaryotic organisms exist in this
time scale?
2. Describe the major environmental changes that have occurred on Earth
a. Climate and Temperature
i. First 2.5 billion years of existence, Earth gradually cooled
ii. Last illio years, Earth’s teperature ostatly flutuates ausig a
alternation between Ice Ages and warmer periods
iii. There are many environments where the temperatures are quite
different such as the tropical rain forest and the Arctic
b. Atmosphere
i. Change in chemical composition, notably oxygen
1. Emergence of living organisms capable of photosynthesis added
oxygen to the atmosphere (currently contains 21% oxygen)
c. Land Masses
i. As Earth cooled, land masses were formed by bodies of water
1. Created terrestrial and aquatic environments
2. Continental Drift: Phenomenon that takes place over billions of
years where continents (major landmasses) have shifted their
positions, changed their shapes, and in some cases become
separated
d. Floods
e. Glaciation
i. Glaciers move across continents and alter the composition of species on
those land masses
ii. Affects water levels of oceans
f. Volcanic Eruptions
i. Eruptions in the ocean can lead to the formation of new islands
(Page 501 Figure 20.9)
ii. Massive eruptions can affect global temperatures and limit solar
radiation by spewing debris into the atmosphere
1. Shift in global temperatures and the limitation of solar radiation
can lead to a limitation in photosynthetic production
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g. Meteorite Impacts
3. Describe how fossils are formed and how we know how old they are
a. Many rocks with fossils are sedimentary
i. Sediments pile up and become rock
ii. Organisms buried quickly and hard parts are replaced by minerals
iii. The older the rock is, the deeper and older organisms are deeper in the
rock bed
b. Fossils can be dated using elemental isotopes in sedimentary rock; radioisotope
dating
i. Radioisotope Dating: A common way to estimate the age of a fossil is
by analyzing the elemental isotopes within the accompanying rock
ii. Radioactive isotopes are unstable and decay at a specific rate
1. Half-life: The length of time required for exactly one half of the
original isotope to decay; unique for each radioactive isotope
a. Scientists can measure the amount of a given isotope as
well as the amount of isotope produced when the
isotope decays
iii. Fossil dating is not conducted on the fossil itself or on the sedimentary
rock
1. Conducted on igneous rock near the sedimentary rock
c. Stromatolite: A layered calcium carbonate structure produced by cyanobacteria
in an aquatic environment
i. Cyanobacteria deplete carbon dioxide in surrounding water, which
causes calcium carbonate to precipitate over the growing mat of
bacterial cells, preserving those cells in those layers
ii. Ancient life forms found in lower strata; newer species found in upper
strata
d. Continental drift – over the past hundreds of millions of years, large land masses
moving over time creating a terrestrial and aquatic environment in which
species can be fossilized
4. Explain the various biases that affect our interpretation of the fossil record
a. Organisms are more likely to become fossilized because of their:
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