DEFINITION OF TERTIARY

The first period of the Cenozoic era, extending

from the end of the Cretaceous of the Mesozoic at 66 million

years ago until the beginning of the Quaternary 1.6 million

years ago. The Tertiary is divided into two periods

including the older Paleogene (66–23.8 Ma) and the younger

Neogene (23.8–1.8 Ma), and further divided into five epochs

including the Paleocene (66–54.8 Ma), Eocene (54.8–33.7

Ma), Oligocene (38.7–23.8 Ma), Miocene (23.8–5.3 Ma),

and Pliocene (5.3–1.6 Ma). The term Tertiary was first

coined by the Italian geologist Giovanni Arduino in 1758,

and later adopted by Charles Lyell in 1833 for his post-

Mesozoic sequences in western Europe. The term Tertiary is

being gradually replaced by the terms Paleogene and Neogene

periods.

The Tertiary is informally known as the age of mammals

for its remarkably diverse group of mammals, including marsupial

and placental forms that appeared abruptly after the

extinction of the dinosaurs. The mammals radiated rapidly in

the Tertiary while climates and seawater became cooler. The

continents moved close to their present positions by the end

of the Tertiary, with major events including the uplift of the

Alpine-Himalayan mountain chain.

Pangea continued to break apart through the early Tertiary

while the African and Indian plates began colliding with

Eurasia, forming the Alpine-Himalayan mountain chain.

Parts of the Cordilleran mountain chain experienced considerable

amounts of strike-slip translation of accreted terranes

with some models suggesting thousands of kilometers of displacement

of individual terranes. The Cordillera of western

North America experienced an unusual geologic event with

the subduction of at least one oceanic spreading ridge

beneath the convergent margin. The boundary between three

plates moved rapidly along the convergent margin from

about 60 million years ago in the north, to about 35 million

years ago in the south, initiating a series of geological consequences

including anomalous magmatism, metamorphism,

and deformation. New subduction zones were initiated in the

southwest Pacific (SE Asia) and in the Scotia arc in the south

Atlantic. The Hawaiian-Emperor seamount chain formed as a

hot-spot track with the oldest preserved record starting about

70 million years ago, and a major change in the direction of

motion of the Pacific plate recorded by a bend in the track

near Midway island formed 43 million years ago.

The San Andreas fault system was initiated about 30

million years ago as the East Pacific rise was subducted

beneath western north America and the relative motions

between the Pacific plate and the North American plate

became parallel to the margin. Around 3.5 million years ago

the Panama arc grew, connecting North and South America

and dramatically changing the circulation patterns of the

world’s oceans and influencing global climate. The East

African rift system began opening about 5–2 million years

ago, forming the sheltered environments that hosted the first

known Homo sapiens.

Climate records show a general cooling of ocean waters

and the atmosphere from the earliest Tertiary through the

Paleocene, with warming then cooling in the Eocene. The

oceans apparently became stratified with cold bottom waters

and warmer surface waters in the Eocene, with further cooling

reflecting southern glaciations in the Oligocene. Late

Oligocene through Early Miocene records indicate a period

of warming, followed by additional cooling in the mid-

Miocene with the expansion of the Antarctic ice sheet that

continued through the end of the Miocene. Pliocene climates

began fluctuating wildly from warm to cold, perhaps as a

precursor to the Pleistocene ice ages and interglacial periods.

The Late Pliocene climates and change into the Pleistocene ice

ages were strongly influenced by the growth of the Panama

arc and the closing of the ocean circulation routes between

the Pacific and Atlantic oceans. The Panama isthmus blocked

warm Caribbean waters from moving west into the Pacific

Ocean but forced these waters into the Gulf Stream that

brings warm water northward into the Arctic Ocean basin.

Warm waters here cause increased evaporation and precipitation,

leading to rapid growth of the northern glaciers.

Nearly all of the mammals present on the Earth today

appeared in the Cenozoic, and most in the Tertiary, with the

exception of a primitive group known as the pantotheres

that arose in the Middle Cretaceous. The pantotheres

evolved into the first marsupial, the opossum, which in turn

branched into the first placental mammals that spread over

much of the northern continents, India, and Africa by the

Late Cretaceous. Pantotheres and earlier mammals laid eggs,

whereas marsupial offspring emerge from an eggshell-like

structure in the uterus early in their development. In contrast,

placental mammals evolve more fully inside the uterus

and emerge stronger with a higher likelihood of surviving

infancy. It is believed that this evolutionary advantage led to

the dominance of placental mammals and the extinction of

the pantotheres.

Mammalian evolution in the Tertiary was strongly influenced

by continental distributions. Some continents like

Africa, Madagascar, India, and Australia were largely isolated.

Connections or land bridges between some of these and

other continents, such as the Bering land bridge between

Alaska and Siberia allowed communication of taxa between

continents. With the land distribution patterns certain families

and orders evolved on one continent, and others on

other continents. Rhinoceroses, pigs, cattle, sheep, antelope,

deer, cats, and related families evolved primarily in Asia,

whereas horses, dogs, and camels evolved chiefly in North

America with some families reaching Europe. Horses have

been used as a model of evolution with progressive changes

in the size of the animals, as well as the complexity of their

teeth and feet.

Marine faunas included gastropods, echinoids, and pelecypods

along with bryozoans, mollusks, and sand dollars in

shallow water. Coiled nautiloids floated in open waters,

whereas sea mammals including whales, sea cows, seals, and

sea lions inhabited coastal waters. The Eocene-Oligocene

boundary is marked by minor extinctions, and the end of the

Pliocene saw major marine extinctions caused by changes in

oceanic circulation with massive amounts of cold waters

pouring in from the Arctic and from meltwater from growing

glaciers.

See also CENOZOIC; NEOGENE.

Title Post:
Rating: 100% based on 99998 ratings. 99 user reviews.
Author:

Terimakasih sudah berkunjung di blog SELAPUTS, Jika ada kritik dan saran silahkan tinggalkan komentar