# Difference between revisions of "Fossils"

 Fossils Earth Science & Study Event Forum Threads 2019 2016 2015 2011 2010 2009 Previous Tests The wiki test exchange has been discontinued as of 2020. Current Test Exchange 2019 Test Exchange Archive There are no images available for this event Question Marathons 2019 2016 2015 Division B Champion Solon Middle School Division C Champion Iolani School

Fossils is an identification event which rotates with Rocks and Minerals every two years. Students identify various fossilized animals and plants from the fossil list, provide details about these organisms such as environment, mode of life, etc., and answer questions on general paleontology.

This page primarily covers information applicable to the event in general - for details on each of the taxa on the identification list, see Fossils/Fossil List.

## Fossil Formation

There are several ways that fossils can form, ranging from the organism being replaced by minerals to the organism getting trapped in amber. This section explains the different types of fossils.

• Mummification: This rare form of preservation preserves life form with some tissue or skin intact. Specimens that are preserved this way are very fragile. Natural mummification usually happens in dry and cold places where preservation happens quickly and effectively. Mummification is not truly fossilization.
• External Molds: These are imprints of the organism embedded in rocks.
• Casts: These are formed when external molds are filled with sediment.
• Internal molds: These occur when sediment fills the shell of a deceased organism such as a bivalve or a gastropod. These remain after the organism's remains decompose to show the internal features of the organism
• Petrification/Petrifaction/Silicification: These occur when minerals slowly replace the various organic tissues of an organism. The most common mineral to cause petrification is silicon, but other minerals also work.
• Carbonization/Coalification: These occur when over time all parts of the original organism except the carbon are removed from the fossil over time. The remaining carbon is the same carbon that the organism was made of.
• Recrystallization: This occurs when original minerals in the fossil over time revert into more stable minerals, such as an apatite shell recrystallizing into the more thermodynamically stable calcite.
• Replacement: This occurs when the hard parts of the organism are replaced with minerals over time.
• Trace fossils: Trace fossils are fossils that are not part of the organism. These include footprints, burrows, eggshells, and coprolite (fossilized excrement). They give insight into an organism's behavior.
• Actual remains: These are much rarer than other fossil types. These are still intact parts of the organism. Actual remains can be seen preserved in ice, tar, or amber. A good example is mammoth hair, which is often frozen and still preserved.
• Tar: When organisms become trapped in tar, due to the oxygen deprived environment, it allows for the rapid burial of body parts which are well preserved. A good example is the La Brea tar pits in Los Angeles.

Fossils almost always form in sedimentary rocks. The extreme heat and pressure needed to form igneous or metamorphic rock often destroys or warps the organism.

When an organism dies, if the conditions are right, it becomes covered in sediments, which, after being subjected to pressure, becomes rock. This takes a very long time, and the actual organism decomposes by then. A soft organism like a worm or jellyfish usually does not get fossilized because it decomposes too fast. Only the hard parts like skeletons and teeth remain long enough to keep the imprint in the rock while the rock is forming.

### Fossil Environments

Fossils form (for the most part) in bodies of water, because sedimentation occurs. Fossilization needs to occur in places where the dead organism will not be disturbed, so a place in the ocean devoid of wave activity is required. Most of these marine fossils do not form in the far depths of the sea known as the Abyssal Zone because the sediment at the bottom of the Abyssal zone is generally dragged into the mantle of the Earth, as opposed to rising to the land.

## Sedimentary Rocks

As said above, fossils usually form in water because sedimentation occurs. Here are some of the common sedimentary rocks that fossils can be found in:

• Sandstones/Siltstones: These rocks can usually be found in off-shore deposits or beaches. They commonly preserve water ripples, tracks, petrified wood, dinosaur bones and hard-shelled invertebrates.
• Conglomerates: Fossilized bones and teeth, as well as amphibian and reptile fossils, can be found in conglomerates.
• Shale: Probably the most common fossil preserving rock, shales can contain fossils that are perfectly preserved. They can contain vertebrates, invertebrates, or plants.
• Limestones: Also a very fossiliferous rock, these represent both shallow and deep tropical seas. Invertebrate fossils, as well as remains of armored fish and shark teeth, can be found in limestones.
• Coal/Coal Shales: Plants, fish, insects, marine invertebrates, and even dinosaur footprints can be found in coal deposits.

Students may be expected to identify sedimentary rocks. Here are some identification tips:

• Coquina: Looks like chewed up oatmeal.
• Diatomite: Similar to chalk limestone, but less chalky and lighter.
• Dolostone: Usually a very light shade of pink.
• Sandstone: Grainy and it does not have to be layered, though it commonly is.
• Limestone Chalk: Looks and feels like chalk.
• Fossiliferous Limestone: Has fossils that are relatively small, but does not have to be covered with fossils.

## Modes of Life

Different animals have different modes of life (these generally refer to oceanic dwellers, which makes up a bulk of the list). The main modes of life are:

• Pelagic: Free swimming, e.g. fish or scallops (scallops "swim" by flapping their shells).
• Sessile: Rooted to the floor, e.g. crinoids (sea lilies) and sea anemones.
• Benthic: Lives on the sea floor, e.g. crabs, lobsters, crinoids.
• Vagrant: Free swimming, same as pelagic.
• Motile: The opposite of sessile; moves around. Examples include anything that is Pelagic/Vagrant, Benthic, or any other organism able to move around.
• Coiled: The outsides of an organism coil around a center point.
• Planktonic: Does not actually swim; floats and is carried along with the ocean's currents.

## Fossils and Time

Fossils are an important part of Earth Science as they provide a look back into what life may have been like many million years ago. Since environments can change significantly over long periods of time, fossils are an important way to see how life may have existed in the past.

### Geologic Time

Earth's history is broken up several ways. The largest section is the supereon. The only one is the Precambrian, lasting from 4500-540 mya (million years ago). After this the next largest are eons. There are four; the Hadean Eon (before 3800 mya), the Archean Eon (3800-2500 mya), the Proterozoic Eon (2500-540 mya) and the Phanerozoic Eon (540 mya to present). Not much is known about the Precambrian, because all of the life forms lacked hard shells or skeletons, making preservation very unlikely. There are, however, fossils called stromatolites that show indications of cyanobacteria. These are first found in the Archaean. It is possible that the first lifeforms and self-replicating RNA strands emerged as early as the mid-Hadean. The Phanerozoic Eon is when shelled invertebrates began to emerge, and the fossil record expands.

The next largest sections are eras. Eras are divided based on the dominant life forms at that time. The Paleozoic (meaning "ancient animals", from 540 mya to 248 mya) was dominated by marine invertebrates. Reptiles dominated the Mesozoic (middle animals) Era (from 248 mya to 65 mya), and mammals dominate the Cenozoic Era (65 mya to present, meaning "recent animals"). We are living in the Cenozoic Era now.

The next breakdown are periods. Each era is broken down into periods, except for the Archaean and Hadean Eons, which are only divided into eras. Periods are broken down into Epochs starting after the beginning of the Phanerozoic Eon. All epochs are then further divided into Ages, which can, though rarely are, divided into Chron. All divisions of time may be distinguished from each other by certain species that lived only in that period, called index fossils. This method is called biogeochronology. These divisions all have counterparts in chronostratigraphy, as Eon/Eonthem, Erathem/Era, System/Period, Series/Epoch, Stage/Age, and Chronozone/Chron.

#### Paleozoic Era

The periods of the Paleozoic:

• Cambrian: (540 mya to 490 mya) The first period, when marine invertebrates start to emerge. Part of the Age of Invertebrates.
• Ordovician: (490 mya to 443 mya) Primitive fish start to form. Index fossil is the trilobite genus Cryptolithus. Part of the Age of Invertebrates.
• Silurian: (443mya to 417 mya) Early land animals began to emerge. Part of the Age of Fishes.
• Devonian: (417 mya to 354 mya) First forests and amphibians form. Index fossils include Mucrospirifer (brachiopod genus) and Phacops (trilobite genus). Part of the Age of Fishes.
• Carboniferous: 354 mya to 290 mya Contains both the Mississippian and Pennsylvanian Periods. Part of the Age of Amphibians.
• Mississippian: (354 mya to 323 mya) Widespread shallow seas form.
• Pennsylvanian: ( 323 mya to 290 mya) Coal-bearing rocks form.
• Permian: (290 mya to 248mya) Earliest gymnosperms (cone-bearing trees). Part of the Age of Amphibians.

#### Mesozoic Era

During the Mesozoic periods, dinosaurs dominated. This entire era is known as the Age of Reptiles.

• Triassic: (248 mya to 206 mya) First dinosaurs and earliest mammals.
• Jurassic: (206 mya to 144 mya) Earliest birds.
• Cretaceous: (144 mya to 65 mya) Flowering plants (angiosperms) develop.

#### Cenozoic Era

The periods in the Cenozoic differ from the other two eras by being broken down even further in epochs. This entire era is known as the Age of Mammals.

• Tertiary: (65 mya to 1.8 mya) Apes begin to appear. It is broken down into epochs:
• Paleocene (65 mya to 54.8 mya) "Age of Birds", lasting through the Eocene.
• Eocene: (54.8 mya to 33.7 mya) Further development of mammals. Giant birds rule the land.
• Oligocene: (33.7 mya to 23.8 mya) Rise of true carnivores.
• Miocene: (23.8 mya to 5.3 mya) Grasses and grazing animals develop.
• Pliocene: (5.3 mya to 1.8 mya) First modern animals.
• Quaternary: (1.8 mya to present) Humans appear and develop. This is the period we are still in today.
• Pleistocene: (1.8 mya to 10,000 ya): First humans.
• Holocene: (10,000 ya to present): The epoch in which we live today. The Holocene is further divided into the Boreal Age, followed by the Atlantic Stage.

Once a new group of organisms becomes dominant after a mass extinction, a new era will be created.

#### New System for Geologic Time

A new system of geologic time was devised early in 2007. It goes like this:

• Tertiary is broken into the Paleogene and Neogene
• Paleogene: Mammals develop from small creatures to diverse animals
• Paleocene
• Eocene
• Oligocene
• Neogene: Hominids develop, animals evolve into roughly modern forms
• Miocene
• Pliocene
• Quaternary
• Pleistocene
• Holocene

As you may have noticed, the changes do not apply to the Quaternary, but for the sake of completeness, this period is included under the modification.

Here is a basic overview of each time period that is specific enough for this event.
Another good geologic time chart that compares the length graphically for all divisions of time.
As of the 2019 season, competitons are required to use the official Science Olympiad geologic time scale.

### Index Fossils

Index fossils are fossils of organisms that lived only in one period. They developed near the beginning of the period, and became extinct before the end. Note that this refers to genera or species, not entire classes or families. Index fossils are extremely useful for dating rock. They can not be used to tell absolute age (we need carbon-14 (or other isotope) testing for that), but can be used for relative dating. By comparing two rock outcrops with the same index fossil, we can conclude that they are roughly the same age, (give or take several million years). To be an index fossil, the organism must have had a wide geographic range, because if a fossil is found only on some barren outcrop in the desert, it can not be used to date rocks from many miles away. It also helps to be fairly common - for instance, dinosaurs of North America are not index fossils because of their rarity.

For example, Genus Mucrospirifer can be an index fossil for the Devonian Period because they only existed during that period. Therefore, if you find a rock with a Mucrospirifer in it, you can guess that the rock is from the Devonian Period.

### Relative Dating

Relative dating orders events in chronological order. It tells which events came first, but it does not tell you the exact date of which it occurred. There are different methods that are used for relative dating: the principle of superposition, the principle of original horizontality, the principle of cross-cutting relationships, and the principle of inclusions.

• Principle of Superposition: If you have undisturbed layers of sedimentary rocks, then the layers will be younger as they near the top. The oldest layers are on the bottom and the youngest layers are on the top.
• Principle of Original Horizontality: Rocks are originally layered horizontally. If you have layers that are higher on one side than on the other, it is due to the tilting of rocks caused by a geological event.
• Principle of Cross-Cutting Relationships: This principle states that a fracture or cut in a rock caused by another rock (igneous intrusion) is always younger than the rock it cuts.
• Principle of Inclusions: Fragments of one rock in another rock must be older than the rock it is contained in.

Also, look: More Laws of Relative Dating

### Absolute Dating

Absolute dating is similar to relative dating in that they both order events in chronological order. However, unlike relative dating, absolute dating can determine the ages of rocks. There are several methods that are used in absolute dating, including radiometric dating, half-life, and carbon dating.

• Half-life: The half-life of an isotope is how much time it takes for half the atoms in that isotope to decay. After that many years, half the atoms in the isotope will decay. After that many years again, half of that half (one-quarter of the whole or two half-lives) will decay. After that many years again, half of the half of that half (one-eighth of the whole or three half-lives) will decay. It will go on until the isotope decays to its daughter product. The table below shows major radioactive isotopes and their half-life. (Ma = million years, Ga = billion years)
Isotope Half-Life
Carbon 14 5730 years
Potassium 40 1.25 Ga
Uranium 235 703.8 Ma
Uranium 238 4.468 Ga
Thorium 232 14.05 Ga
Rubidium 87 48.8 Ga
Samarium 147 106 Ga
• Radiometric Dating: As time goes on, the amount of parent material in a rock decreases as the amount of daughter product in the rock increases. Geologists can determine the age of rocks by measuring the amount of parent and daughter material in the rock and knowing the half-life of the parent rock. The formula is as follows:
$xy = a$

Where y = half-life, x = number of decays, and a = age

## Fossil Symmetry

Most multicellular organisms display some form of symmetry. Humans are bilaterally symmetrical because if you were cut in half from the middle of the front of the head, all the way down the middle, the two sides would look the same.

There are many types of symmetry but the main types are:

• Bilateral Symmetry: Brachiopods are bilaterally symmetrical between each side of each individual valve, and bivalves are bilaterally symmetrical between each valve.
• Radial Symmetry: In your mind, imagine a sand dollar and put it in a circle - from the center of that circle, all the surrounding parts are symmetrical. All echinodermata exhibit radial symmetry.
• Pentamerism: A type of radial symmetry, think of a starfish. They generally have five arms and a center point from which all these arms go out. Pentagonal symmetry, my friends. All echinodermata exhibit this, some in variations.
• Coiled symmetry: Gastropods exhibit it - their shells are coiled around a center point at the apex.
• Spherical symmetry: It is able to be cut into 2 identical halves through any cut that runs through the organism's center

## Competition Tips

### Making a Binder

The majority of your binder should consist of pages on each taxa (genus/order/class/phylum) on the National Fossil list.

What is needed for each page:

Genus-Level Taxa

• Fossil Range
• Taxonomy
• Mode of Life/Diet/Habitat/Distribution)
• Anatomical features, size
• Nicknames, common names
• A picture (or many if there are various forms of the specimen)
• Any other important/trivial info that should go under a misc. section (pop culture, etc)

Orders/Classes

• The common anatomical features throughout the group
• Distinctive features of the said group
• The fossil range of the group
• General habitats and common modes of life
• Common names/Nicknames for group
• Misc. info

Phyla

• A broad range of info and less distinctive features
• There are generally a few main features are shared in these large groups
• Nicknames/Common names (Like Bryozoans are called Sea mats/Moss animals)
• Misc. info

Now keep in mind, these pages should not be used for identification. If you are dedicated to this event, you should be absolutely certain of all ID questions. Only use these pages for time ranges if you forgot or any other info on morphology/adaptations that you can't think of off the top of your head.

Many competitions also require labeling of some sorts, typically anatomical features of a specific phylum, class, etc. It is helpful to be prepared for this and include diagrams of anatomical features of specimen such as trilobites, Phylum Bryozoa, Class Crinoidea, etc.

Binders can be chock full of whatever you put into it. A great binder outweighs any guide, and knowing where every single piece of information lies is a wonderful asset. This is typically one of the more competitive events, so knowing your information well and thoroughly will be a great advantage. Tabbing makes it easy to find what you are looking for. It is especially helpful to make a binder or adapt an old one, because that is when you inadvertently memorize information.

### Available Field Guides

There are 3 main fossil guides used for this event: Simon and Schuster's Guide to Fossils, the Audubon Field Guide, and the Smithsonian (DK) Field Guide.

1. Audubon: It has almost all invertebrates on the list, which automatically puts it first. It has very good information and has everything needed for ID purposes, but it is a bit bulky and specimens are sometimes difficult to find.
2. Smithsonian: Very straight forward, not very bulky, but it does not have all of the specimens on the list. It is much better organized than the Audubon and has better pictures.
3. Simon and Schuster's: It does not have many of the samples, but it is the only guide of the three that has information on dinosaurs. The guide has good general information, but the organization is awkward and some of the fossil information is lacking.

Generally, the best choice as a field guide would be either Smithsonian or Audubon. Smithsonian is better organized and has better pictures, but Audubon has better information. Whichever field guide is chosen, remember to organize, tab, and add things into the field guide to improve it and be able to find information more easily. It is recommended to tab each phylum and group of fossils, as well as plants, trace fossils, and rocks.

Remember: all three books can be used for studying, taking notes, and preparing the binder.

### Day of the Event

If bringing a binder, make sure that everything is hole-punched and organized. It is also okay to have pages in sheet protectors, which includes all notes, the fossil list, pictures, diagrams, etc. If papers are stuffed into the side folders or just placed in, the proctors will remove them and they will be unusable. Make sure to bring plenty of pencils and pens, erasers, and a magnifying glass for live specimens.

## FAQ

How should I prepare for this event?

Create a binder with pages for each fossil, and all the information suggested. You can practice identification in the Fossil ID game under the Question Marathons section of the forum. It cannot be stressed enough to get familiar with your binder. Take practice tests on the test exchange to get familiar with where all the information is, add any useful information from the tests, and also get familiar with the kinds of questions on the tests. Put tabs in your field guide for each of the phyla, highlight specimens in the index, mark the fossil info, and add some notes into your field guide. If you want to do well in this event, know your information thoroughly and do not rely on the field guide nor binder prior to competition.

What can I bring to this event?

A published fossil field guide, one magnifying glass, a pencil, and a 3-ring binder with notes.

What should I put in my binder?

Information on all the genera, at minimum, as well as any necessary information listed on the rule page, such as extinction events or geologic time. However, don't just copy and paste or print pages off of Wikipedia- typing out information yourself helps you learn it, which is a huge advantage. It is also helpful to have a "references section", as many stations have questions regarding the anatomy of specific phyla (so print out lots of diagrams), major mass extinctions, different sedimentary rocks, and methods of fossilization. Having a timeline of the geologic time scale on hand can prove to be useful. Try creating a template for the genera, so you can just fill in the blanks as opposed to re-creating a paragraph. Don't be afraid to print out important pictures in color; having clear pictures can make all the difference in competition. Print double sided if possible. Remember to tab and organize the binder so that it is easier to find the information, as there is not much time to flip through during the competition. If done right, the binder will be more valuable than the field guide. Use practice tests to gain familiarity with the binder (as well as the field guide).

Side Note: Putting pages in page protectors makes it easier to flip through fast, and pages are less likely to rip.

Remember: All pages must be hole punched.

How long should my binder be?

As long as it needs to be. Don't have it be huge to the extent that information is difficult to find; a three-inch binder is likely excessive. Teams with 300+ page binders have placed in this event, but teams with only 70 or so pages have placed as well. It is more important to have information stored in your brain than have it stored in your binder. Still, be sure that everything you might need for competition is available; by spending time building the binder, you will learn a decent amount of the information and will not need as much of the binder itself. Also, be sure you can find everything, so you don't spend too much time flipping through the binder.

What is this event like?

Typically, the event is run in stations, with a set time limit (generally from 1 to 3 minutes). Most tests generally involve identifying a fossil and answering questions about it, such as the taxonomy, time period(s), and mode of life. Some involve pictures of a life form or a picture of something else (like sediment). However, every test is different (as in every study event), so be prepared for surprises. There may not be much time, but remember: every team has the same time limit, so just keep calm, don't rush, and don't waste time. Use partnerships to your advantage; have one partner write down the answers on the answer sheet while another partner flips through the binder to confirm the answers.

## Sample Questions

1. Identify the phylum, genus, and whether it is articulate or inarticulate

3. What is the specimen shown above?

4. How are specimens like this one used by palaeontologists?