Chapter 14 Geologic Time

Cyanobacteria

:Is a blue-green algae thought to be one of the earliest forms of life on Earth.Cyanobacteria first appeared about 3.5 billion years ago.They contained chlorophyll and used photosynthesis. During photosynthesis, they produced oxygen, which helped change Earth's atmosphere.The ozone layer in the atmosphere began to develop, shielding Earth from ultraviolet rays.It is hypothesized that these changes allowed species of single-celled organisms to evolve into more complex organisms.

Eon

An eon is one of the four major subdivisions of geological time.The eon is the longest subdivision ,they are based upon the abundance of certain fossils.here is a limit to how finely geologic time can be subdivided. It depends upon the kind of rock record that is being studied.Sometimes it is possible to distinguish layers of rock that formed during a single year or season. In other cases, thick stacks of rock that have no fossils provide little information that could help in subdividing geological time.

Natural Selection

Charles Darwin was a naturalist who sailed around the world from 1831 to 1836 to study biology and geology.With some of the information about the plants and animals he observed on this trip in mind, he later published a book about the theory of evo-lution by natural selection.In his book, he proposed that natural selectionis a process by which organisms with characteristics that are suited to a cer-tain environment have a better chance of surviving and repro-ducing than organisms that do not have these characteristics.Darwin knew that many organisms are capable of producing more offspring than can survive.This means that organisms compete with each other for resources necessary for life, such as food and living space.

Mesozoic Era

Dinosaurs and other interesting animals lived during the Mesozoic Era, which was between 248 and 65 million years ago. The Mesozoic Era also was marked by rapid movement of Earth's plates.The Mesozoic Era, or the era of middle life, was a time of many changes on Earth.The beginning of the Mesozoic Era, all continents were joined as a single landmass called Pangaea.pangaea separated into two large landmasses during the Triassic Period, the northern mass was Laurasia and Gondwanaland was the southern landmass. As the Mesozoic Era con-tinued, Laurasia and Gondwanaland broke apart and eventually formed the present-day continent.Pieces that had adapted to the new environments survived the mass extinction at the end of the Paleozoic Era.Recall that a reptile's skin helps it retain bodily fluids. This characteristic, along with their shelled eggs, enabled reptiles to adapt readily to the drier climate of the Mesozoic Era. Reptiles became the most conspicuous animals on land by the Triassic Period

Epoch

Epochs are periods that are divided into smaller units of time.They also are characterized by differences in life-forms, but some of these differences can vary from continent to continent. Epochs of periods in the Cenozoic Era have been given specific names.Epochs of other periods usually are referred to simply as early, middle, or late.Epochs are further subdivided into units of shorter duration.

Species

Life scientists often define a species as a group of organisms that normally reproduces only with other members of their group. or example, dogs are a species because dogs mate and reproduce only with other dogs. In some rare cases, members of two different species, such as lions and tigers, can mate and produce offspring.These offspring, however, are usually sterile and cannot produce offspring of their own. Even though two organisms look nearly alike, if the populations they each come from do not interbreed naturally and produce offspring that can reproduce, the two individuals do not belong to the same species.

Era

Next to eons, the longest subdivisions are the eras.Which are marked by major, striking, and worldwide changes in the types of fossils present.For example, at the end of the Mesozoic Era, many kinds of invertebrates, birds, mammals, and reptiles became extinct. Eras are subdivided into periods.

Period

Periods are units of geologic time characterized by the types of life existing worldwide at the time.Periods can be divided into smaller units of time.here is a limit to how finely geologic time can be subdivided.It depends upon the kind of rock record that is being studied.Sometimes it is possible to distinguish layers of rock that formed during a single year or season. In other cases, thick stacks of rock that have no fossils provide little information that could help in subdividing geological time.

Precambrian Time

Precambrian Time is the longest part of Earth's history and includes the Hadean, Archean, and Proterozoic Eons. Precambrian time lasted from about 4.5 billion years ago to about 544 million years ago.The oldest rocks that have been found on Earth are about 4 billion years old. However, rocks older than about 3.5 billion years are rare. This probably is due to remelting and erosion. the Precambrian was the longest interval of geologic time, relatively little is known about the organisms that lived during this time. One reason is that many Precambrian rocks have been so deeply buried that they have been changed by heat and pressure. Many fossils can't withstand these conditions. In addition, most Precambrian organisms didn't have hard parts that otherwise would have increased their chances to be preserved as fossils.

Paleozoic Era

The Paleozoic Era also known a the era of ancient life, began about 544 million years ago and ended about 248 million years ago. Traces of life are much easier to find in Paleozoic rocks than in Precambrian rocks.Warm, shallow seas covered large parts of the continents during much of the Paleozoic Era, many of the life-forms scientists know about were marine, meaning they lived in the ocean. Trilobites were common, and other organisms developed shells that were easily preserved as fossils. The fossil record of this era contains abundant shells,invertebrates were not the only animals to live in the shallow, Paleozoic seas. Vertebrates, or animals with backbones, also evolved during this era. Armoured fish with jaws,lived during the Devonian Period.These fish were so huge that they could eat large sharks with their powerful jaws. Paleontologists know that many ancient fish had lungs as well as gills.Lungs enabled these fish to live in water with low oxygen levels when needed they could swim to the surface and breathe air. By the Pennsylvanian Period, some amphibians evolved an egg with a membrane that protected it from drying out.everal mountain-building episodes occurred during the Paleozoic Era.The first mountain-building episode occurred as the ocean separating North America from Europe and Africa closed.Several volcanic island chains that had formed in the ocean collided with the North American Plate,the collision of the island chains generated high mountains. application sentence:

Geological Time Scale

The appearance or disappearance of types of organisms throughout Earth's history marks important occurrences in geologic time.Paleontologists have been able to divide Earth's history into time units based on the life-forms that lived only during certowever, sometimes fossils are not present.Certain divisions of the geologic time scale are based on other criteria. ain periods.This division of Earth's history makes up the geologic time scale.

Pangea

The end of the Paleozoic Era, sea levels had dropped and the continents had come together to form one giant landmass, the supercontinent Pangaea.Trilobites lived in the oceans, their environment was changed or destroyed.Not all scientists accept the above explanation for the extinctions at the end of the Paleozoic Era, and other possibilities such as climate change have been proposed. As in all scientific debates, you must consider the evidence carefully and come to conclusions based on the evidence.

Cenozoic

The era of recent life, began about 65 million years ago and continues today.Many mountain ranges in North and South America and Europe began to form in the Cenozoic Era.The late Cenozoic, the climate became much cooler and ice ages occurred.The first of these is the Tertiary Period. The present-day period is the Quaternary Period. It began about 1.8 million years ago.Many mountain ranges formed during the Cenozoic Era.The collision crumpled and thickened Earth's crust, raising the highest mountains presently on Earth.Throughout much of the Cenozoic Era, expanding grasslands favored grazing plant eaters like horses, camels, deer, and some elephants.Many kinds of mammals became larger. Although,not all mammals remained on land,Ancestors of the present-day whales and dolphins evolved to live in the sea.Our species,Homo sapiens,probably appeared about 140,000 years ago.People suggest that the appearance of humans could have led to the extinction of many other mammals.

Organic Evolution

The fossil record shows that species have changed over geologic time.This change through time is known as organic evolution.According to most theories about organic evolution, environmental changes can affect an organism's survival. Those organisms that are not adapted to changes are less likely to survive or reproduce. Over time, the elimination of individuals that are not adapted can cause changes to species of organisms.

Trilobite

The term trilobite comes from the structure of the hard outer skeleton or exoskeleton.The exoskeleton of a trilobite consists of three lobes that run the length of the body.Trilobites that lived during one period of the Paleozoic Era showed different characteristics than species from other periods of this era.Paleontologists can use these different characteristics to demonstrate changes in trilobites through geologic time.Trilobites might have been the first organisms that could view the world with complex eyes. Trilobite eyes show the result of natural selection. The position of the eyes on an organism gives clues about where it must have lived.Eyes that are located toward the front of the head indicate an organism that was adapted for active swimming. If the eyes are located toward the back of the head, the organism could have been a bottom dweller.Over time, the eyes in trilobites changed, the trilobite body and tail also underwent significant changes in form through time. Trilobite exoskeletons changed as trilobites adapted to changing environments.Species that could not adapt simply became extinct.