Nature+of+Fossils

 Nature of Fossils

Fossil- a trace of a long-dead organism, and often found in layers of sedimentary rock. Sediment- dust, sand, or mud, deposited by wind or water. Mold-this is a type of fossil, and usually an imprint in rock in the shape of an organisms. Cast-a rocklike model of the organism Some fossils can show forms of behavior and some just capture the appearance of the organism for all of time. Beginning in the late seventeenth century, fossils started being recognized more often. Before this time however, fossils were not noticed but were just known as a part of rocks.
 * Evidence from fossils shows that there is a long history of life on Earth, and because of these findings it shows that organisms appeared, lasted for long periods of time, and then eventually died off, only to be followed by newer forms of life. This is now known as a cycle, of things constantly changing and a tremendous diversity of life-forms.
 * Fossils formed by sediment usually develope from the hard body parts of an organism, such as the shell, bones, teeth, or the woody stem of plants.
 * Over time hard minterals replace the tissue of the organism, leaving rocklike structures.
 * Limestone owes its spongelife texture to the many molds scattered throughout its structure.
 * Some molds are filled with hard minerals which form this cast

In 1668, Robert Hooke published his conclusion about fossils, they are the remains of plants and animals. He was one of the first people to study fossils, mostly petrified wood, with the aid of a microscope. At this time Nicolaus Steno also shared his views with Hooke. Steno propsed the law of superposition-which states that successive layers of rock or soil were deposited on top of one another by wind or water.

Stratum-layer in a cross section of Eath is the oldest, while the top stratum is the most recent. This means that fossils within a single stratum are of the same approximate age.

Using Steno's law the relative age of a fossil can be determined, they could say if a given fossil was older or younger than another fossil. The fossils absolute age could be established with radiological evidence.

Succession of Forms

Precambrian era- began with prokaryotes, different types of organisms arose.

Extinct- organisms appeared, existed for a while and then disappeared

Mass Extinction- brief periods during wihch large numbers of species disappeared.
 * resulted from drastic changes to the enviroment, possibly because of asteroids.
 * ash and dust may have caused blocked sunlight and decreased temperatures around the world.

Trilobite organisms disappeared during the Permian era about 245 million years ago.

Biogeography- the study of geographical distribution of fossils and of living organisms. A comparison of reently formed fossil types with types of living organisms in the same geographic area shows that new organisms arise in areas where similar forms already lived.

When were fossils first noticed and discovered?

How are casts formed?

What is a mass extinction?

What are fossils?

What can they do for us?

What did Robert Hooke conclude? What is Steno's law?