Earth History, Ch. 191 Cenozoic tectonics Final break-up of Pangaea Destruction of Tethys ocean...

Earth History, Ch. 19 1

Cenozoic tectonics

• Final break-up of Pangaea

• Destruction of Tethys ocean– Alpine—Himalaya orogenic belt

Destruction of the Tethyan Seaway

• In Neogene time, Indian Subcontinent and several smaller continental fragments of Gondwanaland collided with Eurasia

• Result was Himalaya Mountains, mountains of the “Near East”, and Alps

• Today, only the Mediterranean Sea, Black Sea, Caspian Sea, and Aral Sea are vestiges of the former Tethyan Seaway

Final driftof IndianSubcontinent

Closure ofTethys Seaway

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

NorthernHemispherecontinentalglaciers

Maximum extent ofPleistocene icecap

Continental glaciationBering Land Bridge was largely ice-free and a corridor for faunal interchange between North America and Asia

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

Oxygenisotoperecord

(these should bepositive numbers)

Displacement of floral ecosystems

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

Great Lakes and Lake Bonneville

Finals

• 4th lecture exam is Wed. @ 10:00am

• Copy of last year’s test is on the web

Maximum extent ofPleistocene icecap

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

Human Evolution:Superfamily Hominoideaincludes gibbons, man,and apes.

Homo is the only genusin Family Hominidae;sapiens is the only speciesin the genus Homo.

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!)

• By latest Miocene time, only one genus had survived: Gigantopithecus

Gigantopithecus

Australopithecines • Earliest true hominids appeared at Miocene-

Pliocene transition, ~5.3 Ma*, the australopithecines– Australopithecus, Paranthropus, et al.

• Australopithecus (4.0-2.3 Ma) was somewhat intermediate in appearance between modern apes and humans (but 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

Australopithecus

“Lucy”, a female of thespecies A. afarensis,found in 3.2 Ma bedsIn Ethiopia

Bi-pedalAustralopithecustracks preservedin volcanic ash,~3.0 Ma, fromTanzania

Reconstruction ofAustralopithecus

Shoulder joint typical ofarborescent apes:long arms, strong wrists, long curved fingers

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

Hominidstratigraphy

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)

Skull of Homo habilis

Brain size vs. mode of life• Brain of all newborn primates = ~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 tree

branches

Brain size vs. mode of life

• Development of large brain may be related to climate change in Africa (~2.5 Ma):– Drying out of climate reduced forests– Life on ground may have paved the way for

prolonged parental care– “Obligatory” bipedalism probably preceeded

increase in brain size

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

Homo erectus

Bones of an 11 or 12 yearold boy (1.6 Ma)

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

Neanderthalburial

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

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

Postscript: New discovery (2002)

Earliest hominid:Sahelanthropus tchadensis,6 to 7 Ma fossils fromChad

Much earlier origin and wider dispersal ofhuman lineage thanpreviously thought

Michel Brunet

bipedalism

climate change

increase in brain capacity

1st widespread hominidEurasian hominid

African emmigrant

(widespread early hominids prior to 5.3 Ma)

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