VIZUALIZING EARTH HISTORYBy Loren E. Babcock
Chapter 12
Cenozoic World
Cenozoic Overview
In the early part of the Cenozoic Era, fragmentation of Pangea
was nearly complete and the world’s continents were
approaching the configuration they have today.
Supercontinent breakup played a role in biogeography.
Separation of Gondwana occurred at a critical phase in the
history of mammals. Australia drifted from the rest of
Gondwana just before the diversification of placental
mammals, leaving the island continent to be inhabited by
marsupials. Elsewhere, the marsupials were largely
outcompeted by placental mammals.
Cenozoic Overview
Cenozoic OverviewDevelopment of the Himalaya Mountains.
One exception to the drifting apart of the continents occurred
on the Indian-Australian Plate.
In the Neogene Period, the Indian subcontinent rammed
into Asia, producing an impressive array of geologic
features that classically illustrate the effects of
continent-continent collision: thrust slices and crustal
thickening, metamorphic zones where suturing has
occurred, an ophiolite sequence, and the highest
mountain peaks on Earth today, the Himalaya Mountains.
Cenozoic OverviewDevelopment of the Himalaya Mountains.
Cenozoic OverviewDevelopment of the Himalaya Mountains.
Cenozoic OverviewThe origin of the Mediterranean Sea.
As the African Plate forged northward, it collided with the
southern margin of Europe in the Mediterranean region, and
the Alps, Apennines, and other mountain ranges of
southern and central Europe rose in a series of events
called the Alpine orogeny.
The long string of mountain chains arising from Spain and North
Africa through Kashmir, India, and the Tibetan Plateau (Nepal
and China), which is called the Alpine-Himalayan orogenic
belt, nearly completely collapsed the once-enormous Tethys
Ocean. The modern Mediterranean Sea is one of the last
vestiges of the Tethys.
Cenozoic OverviewThe factors forcing rapid climate and sea level
change in the late Cenozoic.
Sea level at the beginning of the Paleocene Epoch was low,
but it rose through the epoch, only to fall again in the
Oligocene as the circumpolar current became established
around Antarctica.
From that point forward, Cenozoic sea level history has been
one of rapid and large fluctuations, driven mostly by the waxing
and waning of continental glaciers in polar regions.
Cenozoic OverviewThe factors forcing rapid climate and sea level
change in the late Cenozoic.
The Arctic Ocean remained mostly separated from the
Pacific Ocean through most of the Cenozoic because
the narrow connection between Siberia and Alaska across
the Bering Strait was left unbroken by tectonic processes.
The Bering region emerged as a land bridge between Asia
and North America, allowing animals and plants to migrate between the two
continents.
Sea level changes in the Cenozoic Era had profound effects
on the geographic distributions of animals and plants.
Paleogene Period
Extinctions at the end of the Cretaceous Period opened the
way for adaptive radiations among the survivors, and with
those radiations came life forms of increasingly
modern character.
The Paleogene Period is divided into three epochs, called the
Paleocene, Eocene, and Oligocene. They add up to about
42.5 million years of geologic time, and span the interval
from 65.5 million years ago to about 23 million years ago.
Paleogene PeriodIsolation of Antarctica and Climate Change
Global temperatures rose early in the Eocene Epoch and the
world entered a greenhouse state. In the Eocene, even the poles
were warm, and lush forests grew within the Arctic Circle.
Greenhouse conditions were not to last long. As a consequence
of the dispersal of Gondwanan continental fragments, Antarctica
became isolated within the south polar circle.
Circum-Antarctic current - A circum-polar ocean current
system that flows around Antarctica and isolates it
climatically from South America, Africa, and Australia.
Paleogene PeriodPaleogene Marine Life
Paleogene oceans were filled with life forms that are quite
modern in appearance.
Some marine life forms changed little across the Cretaceous
Paleogene boundary, but became more numerous and diverse.
Mammals multiplied on land during the Paleogene Period, but
some left the land to become successful predators in the sea.
Whales, or cetaceans, made the transition from carnivorous
land mammals to aqueous carnivores during the Eocene Epoch.
Cetacean - A member of the mammal order Cetacea,
which includes whales and porpoises.
Paleogene PeriodPaleogene Marine Life
Birds, the only surviving lineage of land-dwelling theropod
dinosaurs, also had a few representatives in aqueous settings.
Foraminifera suffered pulses of extinction between the middle
Eocene and the early Oligocene, in part related to changing
climatic conditions.
Three important groups of land-dwellers diversified in the
Paleogene: mammals, angiosperms (flowering plants), and
insects.
Paleogene PeriodPaleogene Terrestrial Life
Mammals emerged in the Paleocene Epoch as the inheritors
of a world mostly wiped clean of large terrestrial animals.
Within 10 to 15 million years, the mammals had a toehold in
most terrestrial ecosystems.
Placental mammal - A mammal that nourishes its developing
fetus with a placenta and gives lives birth.
Odd-toed ungulates include horses, rhinoceroses,
hippopotamuses, and tapirs. Horses first appeared as small,
multi-toed animals in the Paleocene Epoch.
Ungulate - A hoofed placental mammal.
Paleogene PeriodPaleogene Terrestrial Life
Perissodactyl - An odd-toed ungulate mammal such as a
horse, rhinoceros, hippopotamus, or tapir.
Artiodactyl - An even-toed ungulate mammal such as a
deer, sheep, goat, pig, cow, camel, llama, or giraffe.
Ruminant - A cud-chewing ungulate mammal such as a bison, cow, or giraffe.
Paleogene PeriodEvolution of the Ungulates
Paleogene PeriodPaleogene Terrestrial Life
Early carnivores, the forerunners of modern wolves, dogs, cats,
bears, pandas, minks, and others, appeared in the Eocene
Epoch, and radiated in the Oligocene Epoch.
Primates were certainly in existence by the early part of
the Paleogene Period, although the earliest lemurs
may have evolved in the Cretaceous Period.
The fossil record of birds in the Paleogene Period includes
large flightless forms. Some species reached the dimensions
of modern ostriches and emus, but they developed powerful
clawed feet and large beaks with which they could subdue
and devour prey.
Neogene Period
The Neogene Period embraces two epochs, the Miocene
and Pliocene, which together lasted almost 17.5 million
years. During this period, the Earth essentially reached its
modern plate configuration, developed much of its modern
biota, and witnessed the magnificent Himalaya Mountains
and the Rocky Mountains reaching skyward.
Uplift of the Colorado Plateau in the western United States
stimulated downcutting through the stratigraphic layers by the
Colorado River (in 10 million years).
Neogene PeriodNeogene Marine Life
One striking aspect of Neogene to Quaternary marine fossils
is their increasingly modern species composition.
The Miocene (from Greek, meion, meaning “few”) was defined as having more than 8% extant
mollusks. The Pliocene (from Greek, pleion, meaning
“more,” and originally spelled Pleiocene) had 50-90% still-
living mollusks. Finally, the Pleistocene (a modification of the
term “post-Pleiocene”) had more than 90% of its
mollusk species still living today.
Neogene PeriodNEOGENE TERRESTRIAL LIFE
Two major factors influenced changes in the terrestrial biota
of the Neogene Period: changing climatic conditions, and
changes in food supplies.
Two groups of plants, the herbaceous plants, or herbs, and
grasses, proliferated in response to changing climate during
across the Paleogene-Neogene transition.
Deer, antelopes, cattle, sheep, pigs, camels, giraffes, and
their kin —all having long teeth— were beneficiaries of the
expansion of silica-rich grasses into open plains.
Neogene PeriodNEOGENE TERRESTRIAL LIFE
The rise of new herbivorous ungulates was probably connected
to changes among carnivores.
Frogs, rodents, songbirds, and some snakes (mostly the
poisonous vipers) all radiated during the Neogene Period.
Insects also make up a large part of the diet of
frogs. For snakes, major food sources are frogs and rodents.
Much of the evolution of primates took place during the
Neogene Period. Monkeys originated in the Oligocene
Epoch, apparently in Africa or Eurasia.
Quaternary PeriodExplain the evolution of humans and their close
relatives.
The most recent 2.5 million years of Earth history is dubbed
the Quaternary Period. It consists of two epochs, the
Pleistocene, or most recent Ice Age; and the Holocene, or
“recent,” the present time.
Glaciers sculpted the landscape of North America and Eurasia,
and mantled the land with rocky sediment (till and outwash).
Similar to the Neogene Period, climate change has been a
dominant theme of Quaternary history. Climate change has
influenced landscape evolution, the geographic distributions
of organisms, and the evolution of organisms.
Quaternary PeriodQUATERNARY LIFE
In the savannahs of Africa, the hominid lineage evolved from
primitive apes during the Neogene and Quaternary periods.
The genus Homo appeared in the Quaternary Period.
Asteroid impacts, recorded in part by tektite fields,
continued into the Quaternary Period.
Marine strata of the Pleistocene Epoch show marine biotas
that are essentially fully modern in species and generic
composition. More than 90% of Pleistocene mollusk
species, for example, are still living today.
Quaternary PeriodQUATERNARY LIFE
Large elephants (wooly mammoths and mastodons) roamed
the Northern Hemisphere near the glacial front. In the
Americas, south of the glacier’s reach, giant ground sloths
and glyptodonts were among the impressive herbivorous mammals.
Through most of the Cenozoic Era, North and South America
maintained dissimilar terrestrial faunas. North American
mammal communities were dominated by placentals, and
South American communities included both placentals and marsupials.
Quaternary PeriodHUMAN EVOLUTION
Hominids and their close relatives have a short evolutionary
History, they belong to the family Hominidae, and date back to
the late Miocene Epoch (6 to 7 million years ago). The hominids
include the extinct australopithecines and Homo.
The modern apes, a sister group to the hominids, include the
bonobos, chimpanzees, gorillas, and orangutans. Fossil
evidence shows that modern humans did not evolve from
any of these apes. The two groups evolved separately
from a common ancestor that existed around the early Miocene, roughly 20 million years ago.
Quaternary PeriodHUMAN EVOLUTION
Species of the genus Homo appeared in the Pleistocene
Epoch, about 2.4 million years ago. In the Pleistocene, the
genus had multiple species, some of which were coeval.
Early hominid species, including early Homo species and
perhaps some australopithecine species, learned how to
make simple tools by chipping flakes from stones and
producing sharp edges.
Quaternary PeriodHUMAN EVOLUTION
Homo erectus, the ancestor of our own species, appeared about
1.8 million years ago. This species migrated to Africa, Europe,
and Asia, and existed until about 200,000 years ago.
Homo erectus had a different skull shape than our species.
The skull was more elongate, and had a low, sloping forehead.
Neanderthals show even more similarities to modern
Humans than does Homo erectus. Neanderthal fossils first
appear in Pleistocene sediments dated at about 200,000
years. They co-existed with Homo sapiens for a long time
until becoming extinct about 30,000 years ago.
Quaternary PeriodHUMAN EVOLUTION
Quaternary PeriodEffects of Quaternary glaciation on the landscape and terrestrial life forms
As Pleistocene glaciers advanced, they eroded the land
surface, polishing resistant rock surfaces.
Streams and valleys were permanently changed as continental
glaciers passed over them.
In addition to the glaciers themselves, wind currents beyond
the limits of the Pleistocene ice sheets played a role in
landscape evolution.
The most recent glacial episode coincided with the extinction of
many large mammals, especially in the Northern Hemisphere.
Quaternary PeriodEffects of Quaternary glaciation on the landscape and terrestrial life forms
Quaternary PeriodEARTH’S PAST, PRESENT, AND FUTURE
Earth’s long, intricate story is not yet complete. This was a
narrative interpreted from the many “pages” of Earth’s
4.5-billion-year history “book”.
The Earth system continues to evolve and to diligently record
the outcome of physical, chemical, and biologic processes in its stratigraphic
“pages.”
Charles Lyell’s principle of uniformitarianism teaches us
that Earth processes are ongoing, and they will continue to
operate in the future as they have in the past.
Humans have, and no doubt will continue to have, a significant
influence over aspects of the Earth systems.