Fossils and Geologic Time

Trilobite: earliest fossil of Arthropods

Fossils can form in several ways. Permineralization occurs when minerals carried by water are deposited around a hard structure.Superposition…

A natural cast forms when flowing water removes all of the original tissue, leaving an impression.

Trace fossils record the activity of an organism.

Relative Dating is Used to Determine the Order of Past Events Relative dating consists simply of knowing which fossils are older or younger. It can be easy to determine this based on which geological deposit they come from and the Law of Superposition. The Law of Superposition is simple and states that the older layer lies underneath the younger layer in undisturbed contexts. Thus, fossils from deeper layers are older than fossils from layers closer to the surface of the earth.

Absolute Dating Gives an Actual Age Absolute dating (or chronometric dating) is based on solar years and gives an actual age reported as “years before present.” Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50,000 years old. It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities.

Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

Preserved remains form when an entire organism becomes encased in material such as ice.

Specific conditions are needed for fossilization. Only a tiny percentage of living things became fossils.

Trilobite: earliest fossil of Arthropods

Radiometric dating provides an accurate way to estimate the age of fossils. Relative dating estimates the time during which an organism lived. It compares the placement of fossils in layers of rock. Scientists infer the order in which species existed.

The Earth’s 4.5 billion year history has been divided and subdivided into time spans delimited by major geological or biological events, such as the development of multicellular life, or mass extinctions. From largest to smallest, the terms for these divisions are: Eon Eons can range from hundreds of millions to more than a billion years. Examples include the Archean, Proterozoic, and Phanerozoic Eons. Era Eons are subdivided into eras, which are intervals of tens to hundreds of millions of years. Examples: Paleozoic, Mesozoic, Cenozoic. Period A period may be tens of millions of years long. Examples: Cambrian, Devonian,Jurassic. Epoch More recent periods are further divided into epochs and ages. Epochs last from tens of thousands to millions of years. Often, periods are simply divided into Early, Middle, and Late Epochs. Other examples are Furongian, Oligocene, and Holocene. Age A typical age lasts for a few million years. Examples: Frasnian, Selandian, Ypresian. We are now experiencing the Holocene Epoch in the Quaternary Period of the Cenozoic Era of the Phanerozoic Eon.

Eras last tens to hundreds of millions of years. consist of two or more periods three eras: Cenozoic, Mesozoic, Paleozoic

Periods last tens of millions of years. most commonly used units of time on time scale associated with rock systems. Epochs last several million years.

Quiz Question 1: What is at the bottom of the geologic time scale? a. the Silurian Period b. the Cenozoic Era c. the oldest division of time d. the youngest division of time E. none seem to be correct

Quiz question 2: What is the shortest division of time in the geologic time scale? a. an epoch b. a period c. an era d. an eon e. a Katzeon

Quiz question 3:What era of geologic time ended with the largest extinction event in Earth history? a. the Cenozoic b. the Cretaceous c. the Paleozoic d. the Mesozoic e. the Katmanozoic f.. the Troyozoic g. the Breazoic

Quiz question 4: What is the longest division of time in the geologic time scale? a. an epoch b. a period c. an era d. an eon e. a Katzpan f. a Shelbyoch

Quiz question 5: What is the current era? a. Archean b. Cenozoic c. Mesozoic d. Paleozoic e. Katzozoic