Tertiary Period

Tertiary Period

In geologic time , the Tertiary Period (also sometimes referred to in terms of a Paleogene Period and a Neogene Period), represents the first geologic period in the Cenozoic Era . The Tertiary Period spans the time between roughly 65 million years ago (mya) and 2.6 mya. When referred to in terms of a Paleogene Period and a Neogene Period, the Paleogene Period extends from approximately 65 mya to 23 mya, and the Neogene Period from 23 mya to 2.6 mya.

The Tertiary Period contains five geologic epochs. The earliest epoch, the Paleocene Epoch , ranges from approximately 65 mya to 55 mya. The Paleocene Epoch is further subdivided into (from earliest to most recent) Danian and Thanetian stages. The second epoch, the Eocene Epoch ranges from approximately 55 mya to 34 mya. The Eocene Epoch is further subdivided into (from earliest to most recent) Ypresian, Lutetian, Bartonian, and Priabonian stages. The third epoch of the Tertiary Period, the Oligocene Epoch ranges from approximately 34 mya to 23 mya. The Oligocene Epoch is further subdivided into (from earliest to most recent) Rupelian and Chattian stages. Following the Oligocene Epoch, the Miocene Epoch ranges from approximately 23 mya to 5 mya. The Miocene Epoch is further subdivided into (from earliest to most recent) Aquitanian, Burdigalian, Langhian, Serravallian, Tortonian, and Messinian stages. The last epoch of the Tertiary Period is the Pliocene Epoch . The Pliocene Epoch is further subdivided into Zanclian and Placenzian stages.

The onset of the Tertiary Period is marked by the K-T boundary or K-T event—a large mass extinction. Most scientists argue that the K-T extinction resulted from—or was initiated by—a large asteroid impact in the oceanic basin near what is now the Yucatan Peninsula of Mexico. The remains of the impact crater , termed the Chicxulub crater, measures more than 105 mi (170 km) in diameter. The impact caused widespread firestorms, earthquakes, and tidal waves. Post-impact damage to Earth's ecosystem occurred as dust, soot, and debris from the collision occluded the atmosphere to sunlight. The global darkening was sufficient to inhibit photosynthesis. Widespread elimination of plant species caused repercussions throughout the food chain as starvation resulted in extinction of the largest life forms with the greatest metabolic energy needs (e.g., the dinosaurs).

At end of the prior Cretaceous Period and during the first half of the Tertiary Period (i.e. the Paleogene Period), Earth suffered a series of intense and large impacts. Large impact craters (greater than 25 mi or 40 km in diameter) include the Kara and Popigal craters in Russia, the Chesapeake crater in Maryland, and the Montagnais crater in Nova Scotia.

The last major impact crater with a diameter over 31 mi (50 km) struck Earth near what is now Kara-Kul, Tajikistan at end of the Tertiary Period and the start of the Quaternary Period .

The extinction of the dinosaurs and many other large species allowed the rise of mammals as the dominant land species during the Tertiary Period.

At the beginning of the Tertiary Period, North America and Europe were separated by a widening ocean basin spreading along a prominent mid-oceanic ridge. North America and South America were separated by a confluence of the future Pacific Ocean and Atlantic Ocean, and extensive flooding submerged much of what are now the eastern and middle portions of the United States. By the start of the Tertiary Period, water separated South America from Africa , and the Australian and Antarctic continents were clearly articulated. The Antarctic continent had begun a southward migration toward the south polar region. At the outset of the Tertiary Period, the Indian subcontinent remained far south of the Euro-Asiatic continent.

By the middle of the Tertiary Period (approximately 30 mya), the modern continental arrangement was easily recognizable. Although still separated by water, the Central American land bridge between North and South America began to reemerge. Antarctica assumed a polar position and extensive ice accumulation began on the continent. The Indian plate drove rapidly northward of the equator to close with the Asiatic plate. Although still separated by a shallow strait of water, the impending collision of the plates that would eventually form the Himalayan mountain chain had begun. The gap between North America and Europe continued to widen at a site of sea-floor spreading along a prominent mid-Atlantic ridge. By the middle of the Tertiary Period, the mid-Atlantic ridge was apparent in a large suture-like extension into the rapidly widening South Atlantic Ocean that separates South America from Africa.

By the end of the Tertiary Period, approximately 2.6 mya, Earth's continents assumed their modern configuration. The Pacific Ocean separated Asia and Australia from North America and South America, just as the Atlantic Ocean separated North and South America from Europe (Eurasian plate) and Africa. The Indian Ocean washed between Africa, India, Asia, and Australia. The Indian plate driving against and under the Eurasian plate uplifted both, causing rapid mountain building. As a result of the ongoing collision, ancient oceanic crust bearing marine fossils was uplifted into the Himalayan chain.

Climatic cooling increased at the end of the Tertiary Period, and modern glaciation patterns became well-established.

See also Archean; Cambrian Period; Dating methods; Devonian Period; Evolution, evidence of; Evolutionary mechanisms; Fossils and fossilization; Historical geology; Holocene Epoch; Jurassic Period; Mesozoic Era; Mississippian Period; Ordovician Period; Paleozoic Era; Pennsylvanian Period; Phanerozoic Eon; Pleistocene Epoch; Precambrian; Proterozoic Era; Silurian Period; Supercontinents; Triassic Period