Science Olympiad Fossils Division B 2015 5 - Index Fossils

Index Fossils

• What are they good for?

Index Fossils

Index fossils

(also known as guide fossils, indicator fossils , key fossils or type fossils) or zone fossils) are fossils used to define and identify the premise that, although different sediments geologic periods (or faunal stages). They work on may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil. If the species concerned were short-lived (in geological terms, lasting a few hundred thousand years), then it is certain that the sediments in question were deposited within that narrow time period. The shorter the lifespan of a species, the more precisely different sediments can be correlated, and so rapidly evolving types of fossils are particularly valuable. The best index fossils are common, easy-to-identify at species level, and have a broad distribution —otherwise the likelihood of finding and recognizing one in the two sediments is minor.

1] Geologists use both large fossils (called macrofossils ) and microscopic fossils (called microfossils) for this process, known as biostratigraphy . Macrofossils have the advantage of being easy to see in the field, but they are rarer, and microfossils are very commonly used by oil prospectors and other industries interested in mineral resources when accurate knowledge of the age of the rocks being looked at is needed.

From Web Site: Wikipedia The series of deposits that spans the occurrence of a particular index fossil, is often referred to as that fossil's zone, enabling to relate different faunas through time. An example would be to say that

Mesolenellus hyperborea

occurs in the late

Nevadella

-zone .

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Index Fossils

A good index fossil is one with four characteristics: – it is distinctive, – widespread, – abundant and limited in geologic time. • Because most fossil-bearing rocks formed in the ocean, the major index fossils are marine organisms. (Does not mean all index fossils are from the Oceans.) • Any type of organism can be distinctive, but not so many are widespread. Many important index fossils are of organisms that start out life as floating eggs and infant stages, which allowed them to populate the world using ocean currents. The most successful of these became abundant —and at the same time, they became the most vulnerable to environmental change and extinction. That boom-and-bust character is what makes the best index fossils.

• Web Site: http://geology.about.com/od/glossaryofgeology/g/Index-Fossils.htm

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Index Fossils

Other major index fossils are small or microscopic, part of the floating plankton in the world ocean. These are handy because of their small size. They can be found even in small bits of rock, such as wellbore cuttings. Because their tiny bodies rained down all over the ocean, they can be found in all kinds of rocks. Therefore the petroleum industry has made great use of index microfossils, and geologic time is broken down in quite fine detail by various schemes based on graptolites, fusulinids, diatoms and radiolarians.

• For terrestrial rocks, which form on land, regional or continental index fossils may include small rodents that evolve quickly as well as larger animals that have wide geographic ranges. These form the basis of provincial time divisions .

• Index fossils are used in the formal architecture of geologic time for defining the ages, epochs, periods and eras of the geologic time scale. Related fossil types include the characteristic fossil —a fossil that belongs to a time period but doesn't define it —and the guide fossil, one that helps narrow down a time range rather than nail it down.

• Web Site: http://geology.about.com/od/glossaryofgeology/g/Index-Fossils.htm

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Index Fossils

Examples of index fossils include: Ammonites

were common during the Mesozoic Era (245 to 65 mya), They were not found after the Cretaceous period , as they went extinct during the K-T extinction (65 mya).

Brachiopods

(mollusk-like marine animals) appeared during the

Cambrian

500 mya); some examples still survive. (540 to

Graptolites

(widespread colonial marine hemichordates) that lived from the Cambrian period (roughly 540 to 505 million years ago) to the early to mid Carboniferous (360 to 320 million years ago).

Nanofossils

are microscopic fossils (the remains of calcareous nannoplankton, coccolithophores) from various eras. Nanofossils are very abundant, widely distributed geographically, and time-specific, because of their high evolutionary rates. There are enormous numbers of useful nanofossils, including radiolarians and foraminifera. Nanofossils are the primary method of dating marine sediments.

Trilobites

were common during the Paleozoic Era (540 to 245 mya); about half of the Paleozoic fossils are trilobites. They evolved at the beginning of the Paleozoic Era and went extinct during the late Permian period (248 million years ago). • From Web Site: http://www.enchantedlearning.com/subjects/dinosaurs/glossary/IndexFossils.shtml

Questions ?

Next Week’s Topics?

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Taxonomic hierarchy

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Review Test

Flash Cards Instructions

1. Divide the work between team members 2. Check each others work 3. Work on the fossils assign to your team 4. Use the sample flash cards posted to the schools Science Olympiad web site under the Fossil event. Sample Files are: 1. FlashCardsFusulinidsNummulites.ppt

2. FlashCardsHemichordataMucrospirifer.pptx

5. Save your flash card files using this name: 1. FlashCards

Name of FossileName of Fossil Example is:

FlashCardsFusulinidsNummulites.ppt

For Fossil pictures start with these 3 files loaded on the school Science Olympiad web site 2009-Fossil-Poster.pdf

2009-Fossil-Notes-B.pdf

2009-Fossil-Notes-B2.pdf

Another good source is: Web Site: http://scioly.org/wiki/index.php/Fossil_List