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 Cenozoic Paleogene Neogene Paleocene Eocene Oligocene Miocene Pliocene Pleistocene 65 24 5.3 1.8 12,000 years Holocene
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Earth History, Ch. 19 1faculty.chas.uni.edu/~groves/EHCh19lecturept1.pdfEarth History, Ch. 19 15 Earliest hominids • Sahelanthropus is an intermediate between early apes and first
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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
Earth History, Ch. 19 2
Today’s outline
• Glaciation
• Human evolution
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
Earth History, Ch. 19 4
Northern
Hemisphere
continental
glaciers
Earth History, Ch. 19 5
Continental glaciation• Bering Land Bridge was ice-free and a corridor for faunal
interchange between North America and Asia
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
Earth History, Ch. 19 7
Oxygen
isotope
record
(these should be
positive numbers)
Earth History, Ch. 19 8
Displacement of floral
ecosystems
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
Earth History, Ch. 19 10
Great Lakes and Lake Bonneville
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
Earth History, Ch. 19 12
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.
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!)
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
Earth History, Ch. 19 16
Sahelanthropus tchadensis
Discovered in 2002 by
Dr. Michel Brunet
Earth History, Ch. 19 17
Australopithecus
“Lucy”, a female of the
species A. afarensis,
found in 3.2 Ma beds
In Ethiopia
Earth History, Ch. 19 18
Bi-pedal
Australopithecus
tracks preserved
in volcanic ash,
~3.0 Ma, from
Tanzania
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
Earth History, Ch. 19 20
Hominid
stratigraphy
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)
Earth History, Ch. 19 22
Hominid brain capacity
Earth History, Ch. 19 23
skull of Homo habilis
2.5 Ma stone tools
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
Earth History, Ch. 19 25
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
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
Earth History, Ch. 19 28
Homo erectus
Bones of an 11 or 12 year
old boy (1.6 Ma)
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