8-2.2 Vocabulary 10/21/14 Fossil: the preserved remains or traces of an organism that lived in the past, usually more than 10,000 years ago Fossil Record: Fossil Record: gives important information about past life and
environments on Earth Cast Fossil: Forms when a mold is filled with sand or mud that hardens into the shape of the organism Mold Fossil: Forms when sediments bury an organism and the sediments change into rock; the
organism decays leaving a cavity in the shape of the organism MOLDS AND CASTS A mold forms when hard parts of an organism are buried in sediment, such as sand, silt, or clay. MOLD FOSSIL This mold, or imprint, is of
an extinct mollusk called an ammonite. The hard parts completely dissolve over time, leaving behind a hollow area with the organisms shape. A cast forms as the result of a mold. Water with dissolved minerals and sediment fills the molds empty spaces.
CAST FOSSIL This ammonite cast was discovered in the United Kingdom. Minerals and sediment that are left in the mold make a cast. A cast is the opposite of its mold.
Trace Fossil: Forms when mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind TRACE FOSSILS Trace fossils show the activities of organisms. An animal makes a footprint when it steps in sand or mud.
FANCY FOOTWORK This dinosaur footprint was found in Namibia, Africa. Over time the footprint is buried in layers of sediment. Then, the sediment becomes solid rock.
Carbonized Fossil: Forms when organisms or parts, like leaves, stems, flowers, and fish are pressed between layers of soft mud or clay that hardens squeezing almost all the decaying organism away leaving the carbon imprint in the rock CARBON FILMS All living things contain an
element called carbon. When an organism dies and is buried in sediment, the materials that make up the organism break down. FERN FOSSIL This carbon-film fossil of a fern is more than 300 million years old.
Eventually, only carbon remains. The thin layer of carbon left behind can show an organisms delicate parts, like leaves on a plant. Preserved Fossil: Forms when an entire organism or parts
of an organism are prevented from decaying by being trapped in rock, ice, tar, or amber PRESERVED REMAINS Some organisms get preserved in or close to their original states. Here are some ways that can happen. Amber
An organism, such as an insect, is trapped in a trees sticky resin and dies. More resin covers it, sealing the insect inside. It hardens into amber.
Tar An organism, such as a mammoth, is trapped in a tar pit and dies. The tar soaks into its bones and stops the bones from
decaying. Ice An organism, such as a woolly mammoth, dies in a very cold region. Its body is frozen in ice,
which preserves the organism even its hair! Petrified Fossil: Forms when minerals soak into the buried remains, replacing the remains, and changing them into rock PETRIFIED FOSSILS
The word petrified means turning into stone. Petrified fossils form when minerals replace all or part of an organism. PETRIFIED FOSSIL The Field Museum in Chicago displays a fossil of a Tyrannosaurus rex.
Water is full of dissolved minerals. It seeps through the layers of sediment to reach the dead organism. When the water evaporates, only the hardened minerals are left behind. HOW IS A FOSSIL FORMED?
1. Sediment An animal is buried by sediment, such as volcanic ash or silt, shortly after it dies. Its bones are protected from rotting by the layer of sediment.
2. Layers 3. Movement 4. Erosion More sediment layers accumulate above the animals remains, and
minerals, such as silica (a compound of silicon and oxygen), slowly replace the calcium phosphate in the bones. Movement of tectonic plates, or giant rock slabs that make up
Earths surface, lifts up the sediments and pushes the fossil closer to the surface. Erosion from rain, rivers, and wind wears away the remaining rock layers. Eventually, erosion or people
digging for fossils will expose the preserved remains. How do fossils form? The process of forming fossils is very difficult. The conditions have to be just right!
