TRIASSIC PERIOD

What is the Triassic period and how did it get its name?

The Triassic period follows the Permian period on the geological time scale. During this time, dinosaurs first began to evolve from the early reptiles, the first primitive mammals appeared, and the armored amphibians and mammal-like reptiles died out. The Triassic was one of the first labeled divisions on the geologic time scale, and it is the first of three periods (the others are the Jurassic and Cretaceous) making up the Mesozoic era.

The Triassic was first named in 1834 by German geologist Friedrich August von Alberti (1795-1878) to describe a three-part division of rock types in Germany. It was originally called the Trias, and is still called this by many European geologists. It is named after three, or tri, layers of sedimentary rocks representative of the time period: from bottom to top, a sandstone, limestone, and copper-bearing shale. The three distinct rock formations are, from the bottom up, the Bunter (mostly Early Triassic), the Muschelkalk (Middle Triassic), and the Keuper (mostly Late Triassic).

How long did the Triassic period last?

The geologic time scale is not exact, and depending on the country or scientist, the dates of the Triassic period can vary by about 5 to 10 million years. On the average, the Triassic period is said to have lasted from about 250 to 205 million years, for a total of about 45 million years in length.

What are the divisions of the Triassic period?

In general, the informal way to define parts of the Triassic period is to use the terms early, middle, and late Triassic. More formally, they are capitalized (Early, Middle, and Late), or sometimes (Lower, Middle, and Upper) and include subdivisions within those groupings. The following lists a general interpretation of the Triassic epochs (although note that many researchers use slightly different notations; for example, many do not list the Rhaetian Age):

Triassic Period

Epoch

Age

Millions of Years Ago (approximate)

Early

Olenekian

245-242

Induan

250-245

Middle

Ladinian

234-227

Anisian

242-234

Late

Rhaetian

210-205

Norian

221-210

Carnian

227-221

What did the Triassic period signify?

The Triassic period represented the time after the great Permian period extinctions. It also was important as a time of transition when the old life of the Paleozoic era gave way to the more highly developed and varied form of life of the Mesozoic era. The Permian period extinctions wiped out most of the animals and plants on Earth (about 90 percent of all species), making the very early Triassic an eerie place, almost completely devoid of the abundant life that existed perhaps hundreds or thousands of years before. Certain flora and fauna still dotted the land, and eventually, after about 10 million years or more, life began to emerge in full force again. But it still took even longer for larger animals, coral reefs, and other specialized animals to recover or evolve after the extinction at the end of the Permian period.

CONTINENTS DURING THE TRIASSIC PERIOD

Do Earths continents change positions?

Yes, the continents continually change positions, but it takes them millions of years to shift and move great distances. Earths continents are actually part of the thick plates that make up the planets crust, all of various sizes and shapes. These plates fit together like a jigsaw puzzle. They do not move fast only fractions of an inch to inches per year.

What are continental drift and plate tectonics?

The reason (or reasons) for Earths crustal movement is still somewhat of a mystery. The most accepted theory of plate movement is called continental drift, and the theory of its mechanism, plate tectonics. These theories suggest that the continental plates move laterally across the face of the planet, driven by the lower, more fluid mantle. At certain plate boundaries, molten rock from the mantle rises at a mid-ocean ridge (such as the Mid- Atlantic Ridge, a long chain of volcanic mountains that lie under the Atlantic Ocean); or its equivalent on land, the rift valley (such as the one in eastern Africa), the magma solidifying and moving away to either side of the ridge. At other plate boundaries, plates are pushed under an adjacent plate, forming a subduction zone, in which the crust sinks into the mantle again. And at other boundaries, plates just slip by each other, such as the San Andreas Fault in California, in which a part of the North American plate slides by the Pacific plate.

But not everyone agrees on these theories. One reason is because, although the idea of moving plates seems sound, the mechanisms for developing plate tectonics is not fully understood. Therefore, some scientists believe in continental drift, but not plate tectonics. Many of these scientists believe that the reason that the continents shift is that Earth is actually expanding, causing a false illusion of movement (although no one can explain why or how Earth is expanding). Another hypothesis is called surge tectonics, in which the features of Earths surface are explained by the sudden surge of plate movement, as opposed to a constant flow by the steady movement of the mantle. And still others suggest that the continents have always been in the same positions.

No one really can fully explain the reason for the continual movement of the plates. One thing is certain: the plates do move. Since the advent of Earth-orbiting observation satellites, scientists have been able to track the plates using sophisticated laser-ranging instruments that measure the minute movements.

Hundreds of millions of years ago the seven continents were joined together as a supercontinent scientists now call Pangea. It later broke up into Laurasia and Gondwanaland during the Triassic, and eventually split apart even more (based on a U.S. Geological Survey map).

 
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