earth history, ch. 19 1faculty.chas.uni.edu/~groves/ehch19lecturept1.pdfearth history, ch. 19 15...
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Earth History, Ch. 19 1
Ch. 19—The Neogene World
• Neogene Period
includes Miocene,
Pliocene and
Pleistocene epochs
• Beginning of
Holocene was
approx. 12,000
years ago
Cen
ozo
icPaleogene
Neogene
Paleocene
Eocene
Oligocene
Miocene
Pliocene
Pleistocene
65
24
5.3
1.812,000 years
Holocene
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Earth History, Ch. 19 2
Today’s outline
• Glaciation
• Human evolution
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Earth History, Ch. 19 3
Continental glaciation
• Early Neogene climate was relatively mild
• In mid-Pliocene time, ~3.2 million years
ago, modern ice age began
• Ice age continues today, although glacial
maxima and minima are cyclical, and we
are now in an “interglacial” episode
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Earth History, Ch. 19 4
Northern
Hemisphere
continental
glaciers
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Earth History, Ch. 19 5
Continental glaciation• Bering Land Bridge was ice-free and a corridor for faunal
interchange between North America and Asia
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Earth History, Ch. 19 6
Waxing and waning of glaciers
• High frequency glacial and interglacial cycles:
– Periodic changes in the tilt of Earth’s axis relative to
plane of orbit
– Periodic changes in the orbit itself, due to gravitational
pull of other planets
• Cycles can be documented through oxygen
isotope records
• Waxing and waning has displaced plant
ecosystems by up to 20° latitude
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Earth History, Ch. 19 7
Oxygen
isotope
record
(these should be
positive numbers)
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Earth History, Ch. 19 8
Displacement of floral
ecosystems
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Earth History, Ch. 19 9
Origin of the Great Lakes and
Lake Bonneville
• Retreat of glaciers after the most recent
glacial interval left behind large basins that
eventually filled with water
– Great Lakes formed within the past 10,000 to
15,000 years
– Lake Bonneville covered much of Utah; now
the Great Salt Lake is a “tiny” remnant
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Earth History, Ch. 19 10
Great Lakes and Lake Bonneville
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Earth History, Ch. 19 11
What was the ultimate cause of
Pliocene-Pleistocene glaciation?
• Probably related to creation of Isthmus of
Panama
– Modification of global ocean currents
– Separation of Atlantic and Pacific oceans
resulted in dramatic cooling of Arctic Ocean
water
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Earth History, Ch. 19 12
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Earth History, Ch. 19 13
Human Evolution:
Superfamily Hominoidea
includes gibbons, man,
and apes.
Homo is the only genus
in Family Hominidae;
sapiens is the only species
in the genus Homo.
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Earth History, Ch. 19 14
Early origins
• Earliest “hominoid” fossils are from Africa, ~20 Ma (early Miocene)
• These early “hominoids” are probably ancestral to both modern hominids and pongiids, but fossil record is spotty
• mid- to late-Miocene was a time of “hominoid”radiation throughout Africa and Eurasia (more “apes” then than now!)
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Earth History, Ch. 19 15
Earliest hominids
• Sahelanthropus is an intermediate between early apes and first true hominids
– Known from Chad in beds 6-7 Ma
• Earliest true hominids appeared at ~5.3 Ma, the australopithecines
– Australopithecus, Paranthropus
• Australopithecus (4.0-2.3 Ma) was intermediate in appearance between modern apes and humans (not an evolutionary intermediate):
– Males larger than females (4.5 ft vs. 3.5 ft)
– Brain size barely larger than modern chimp
– Bi-pedal, but spent much time in trees
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Earth History, Ch. 19 16
Sahelanthropus tchadensis
Discovered in 2002 by
Dr. Michel Brunet
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Earth History, Ch. 19 17
Australopithecus
“Lucy”, a female of the
species A. afarensis,
found in 3.2 Ma beds
In Ethiopia
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Earth History, Ch. 19 18
Bi-pedal
Australopithecus
tracks preserved
in volcanic ash,
~3.0 Ma, from
Tanzania
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Earth History, Ch. 19 19
Early Homo
• Australopithecus branched into at least two
species (A. afarensis and A. africanus)
• earliest Homo originated from
Australopithecus approximately 2.4 Ma
• By 2.0 Ma, at least two species of early
Homo were in existence
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Earth History, Ch. 19 20
Hominid
stratigraphy
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Earth History, Ch. 19 21
Early Homo
• Characteristics of early Homo:
– Large brain (800 cm3 vs only 450 cm3 for
Australopithecus)
– Smaller teeth
– Ability to make and use stone tools
• Meat in diet
– Spent most of the time on the ground (not in
trees)
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Earth History, Ch. 19 22
Hominid brain capacity
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Earth History, Ch. 19 23
skull of Homo habilis
2.5 Ma stone tools
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Earth History, Ch. 19 24
Brain size vs. mode of life
• Brain of all newborn primiates = ~10% of body weight
– Brain growth stops shortly after birth in monkeys and apes
– Brain growth continues for ~1 year in Homo
• Homo development is delayed relative to chimps and apes
• Delayed maturation of Homo requires significant parental care
– Parents must hold babies, thus arms not free to hold onto tree branches
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Earth History, Ch. 19 25
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Earth History, Ch. 19 26
Brain size vs. mode of life
• Development of large brain may be related
to climatic change in Africa (~2.5 Ma):
– Drying out of climate reduced forests
– Life on ground may have paved the way for
prolonged parental care
– Bipedalism probably preceeded increase in
brain size
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Earth History, Ch. 19 27
Homo erectus
• Homo erectus evolved from early Homo
approximately 1.6 Ma
• First hominid to migrate beyond Africa
– “Peking Man”, “Java Man”
• Looked similar to modern humans, but:
– Slightly smaller brain (1000 cm3 vs 1400 cm3)
– Narrower pelvis
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Earth History, Ch. 19 28
Homo erectus
Bones of an 11 or 12 year
old boy (1.6 Ma)
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Earth History, Ch. 19 29
Homo neanderthalensis
• Neanderthal fossils are known in Eurasia in beds ranging from 100,000 to 35,000 years old
– Probably originated from a European or Asian population of H. erectus or related species
• Fossils commonly found in cave deposits
– Probably practiced some form of religion
– Buried dead family members with food and tools
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Earth History, Ch. 19 30
Neanderthal
burial
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Earth History, Ch. 19 31
Homo sapiens
• Homo sapiens (modern humans) originated
in Africa ~150,000 ybp (presumably from
an African popolation of H. erectus or
related species)
• DNA from H. sapiens and H.
neanderthalensis indicates that ancestral
populations may have diverged by 500,000
ybp
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Earth History, Ch. 19 32
Homo sapiens
• Homo sapiens seemingly stayed in Africa
for several tens of thousands of years before
migrating to Europe
• Oldest European fossils of H. sapiens are
~33,000 ybp—about the same time H.
neanderthalensis vanished