BIOL 1F90 Study Guide - Midterm Guide: Phanerozoic, Igneous Rock, Cyanobacteria
20 Apr 2016
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BIOLOGY MIDTERM EXAM REVIEW
Chapter 20.2 – History of Life on Earth
− Universe began with the Big Bang 13.7 bya
− Solar system began about 4.6 bya
− The Earth is 4.55 billion years old
o 4 bya, the Earth cooled enough for outer layers to solidify and oceans to form
o 4 bya to 3.5 bya, first life on Earth was evident
− Geological Timescale: A tielie of Earth’s histor fro it’s origi . illio ears ago a to
the present (Page 499 Figure 20.7)
o Subdivided into 4 eons, which are further divided into eras
▪ Eons:
• Phanerozoic
• Precambrian
o Proterozoic
o Archean
o Hadean (oldest)
o Zoic means animal life
Environmental and Biological Changes
− Interactive processes that influenced change in living organisms:
o Genetic changes in organisms
▪ Impacts an organisms ability to survive in their native environment
o Environmental influences
▪ Influences the types of organisms that have existed during different periods
▪ Can cause extinction or the reproduction of new species
− The interactive processes are often correlated with the following major environmental changes:
o Climate and Temperature
▪ First 2.5 billion years of existence, Earth gradually cooled
▪ Last illio ears, Earth’s teperature ostatl flutuates ausig a
alternation between Ice Ages and warmer periods
▪ There are many environments where the temperatures are quite different such
as the tropical rain forest and the Arctic
o Atmosphere
▪ Change in chemical composition, notably oxygen
• Emergence of living organisms capable of photosynthesis added
oxygen to the atmosphere (currently contains 21% oxygen)
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o Land Masses
▪ As Earth cooled, land masses were formed by bodies of water
• Created terrestrial and aquatic environments
• 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
o Floods
o Glaciation
▪ Glaciers move across continents and alter the composition of species on those
land masses
▪ Affects water levels of oceans
o Volcanic Eruptions
▪ Eruptions in the ocean can lead to the formation of new islands (Page
501 Figure 20.9)
▪ Massive eruptions can affect global temperatures and limit solar radiation by
spewing debris into the atmosphere
• Shift in global temperatures and the limitation of solar radiation can
lead to a limitation in photosynthetic production
o Meteorite Impacts
Mass Extinctions
− Mass Extinction: Many species go extinct at the same time
− 5 large mass extinctions occurred near the end of the Ordovician, Devonian, Permian, Triassic,
and Cretaceous periods (Page 500 Figure 20.8)
o Geological eras are often defined by biological extinctions and adaptive radiations (and
other major events)
Fossils
− Fossils: Recognizable remains of past life on Earth
− Paleontologist: Scientists who study fossils
o Often studies changes in life forms over time by studying the fossils in various strata
(Page 501 Figure 20.10)
− Fossil Records: The record of the life forms that existed during particular geological periods
o Great bulk of the fossil record is dominated by the remnants of animals with shells and
by the microscopic remains of plants and animals
o Paleontologists expect the fossil record to underestimate the actual date that a species
came into existence because they are unlikely to find the first member of the species
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o Biases in the fossil record:
▪ Organisms are more likely to become fossilized because of their:
• Anatomy – hard parts vs. soft bodies
• Size – large vs. small
• Number – abundant vs. rare
• Environment – marine/near water vs. inland
▪ Geological Processes
• Favours fossilization of certain types of organisms
• Can also cause parts of different species to be mixed in after death
▪ Time – more recent vs. ancient
▪ Paleontological Interests
• Scientific interests may favour searching for and analyzing certain
species over others
− Many rocks with fossils are sedimentary
o Sediments pile up and become rock
o Organisms buried quickly and hard parts are replaced by minerals
o The older the rock is, the deeper and older organisms are deeper in the rock bed
− Fossils can be dated using elemental isotopes in sedimentary rock; radioisotope dating
o Radioisotope Dating: A common way to estimate the age of a fossil is by analyzing the
elemental isotopes within the accompanying rock
o Radioactive isotopes are unstable and decay at a specific rate
▪ Half-life: The length of time required for exactly one half of the original isotope
to decay; unique for each radioactive isotope
• Scientists can measure the amount of a given isotope as well as the
amount of isotope produced when the isotope decays
o Fossil dating is not conducted on the fossil itself or on the sedimentary rock
▪ Conducted on igneous rock near the sedimentary rock
Archean Eon
− Time when diverse microbial life grew in ancient oceans
− Prokaryotic cells arose (first cells); influenced by energy (same as eukaryotic cells)
o Divided into 2 domains:
▪ Bacteria
▪ Archaea
• Arose in the early extreme environments
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