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.