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Diapositiva 1

• fossil
• Fossils are the preserved evidence in rocks or soil of organisms that once excited o n earth
• There are 4 types of fossils
• -Original
• -Replancement
• -Carbon film
• -Indirect fossils
• Original fossil
• The organism's preserved and original chemical structure remains almost the same
• E.g complete skeleton, bones or tooth or shell
• Made of calcium carbonate resistant to decay
• Replacement Fossil
• Forms when part of the organisms is chemically changed
• Takes a long time
• Usually the calcium carbonate turns into silica-silicon dioxide- like sand
• Sometimes it turns into opal Another form of silica
• If the material being replaced is wood- it is referred to as petrified
• Petefication
• Minerals can replace tissues(organs,muscles,skin)
• In animals, minerals fill the tiny spaces in the hard tissues(like bone)
• In trees, minerals replace the wood,so the wood becomes rock.
• Carbon film and indirect fossils
• Occur when dead bodies partially decay leaving thin black layers of carbon
• Also called carbon trace fossils
• Still in the shape of organism and shows the fine detail coal is made this way
• Indirect fossils are not part of the organism itself-but preserved remains of the imprints of the bodies i.e footprints, or tacks, burrows and dung (trace fossil)
• Moulds are imprints of the outside of an organism- it’s a negative image
• Internal moulds and casts
• If the mould is of the inside of an organism- it could be if a small shell fills up with mud-hardens and turns to rock-and the shell is then decayed away
• Casts: when an organism in rock decays-the space in the rocks fills with soil which then turns into rock-leaving a copy of the outside of the organism- positive image and three dimensional
• Moulds&Cast
• Mould= the print/impression left in sediment/rock where the plant/animal was bruised
• Cast=forms when sediment fills a mould and becomes rock.
• Both can show what the inside or outside of an organism looked like.
• Preserving environment
• Usually when an organism dies, it begins to decay right away.
• But sometimes organisms are buried by sediment when they die
• Sediment can preserve the organism
• Hard parts(shells, teeth,bones) are preserved more often than soft parts(skin,organs).
• These parts becomes fossils when the sediment harden to form a sedimentary rock
• Fossil in Amber
• Sometimes organisms(such as insects,frogs and lizards) are caught in sticky tree sap
• If the sap hardens around the insect a fossil is created.
• Hardened tree sap is called amber
• Frozen fossils- Permafrost
• Ice and cold temperatures slow down decay
• Fossil can be preserved in blocks of ice
• Fossils of wooly mammoths, relatives of elephants that went extinct 10,000 years ago, have been found in ice.
• One was found of a baby mammoth in 2007 in Russia
• Fossils in Asphalt/Tar
• In some places,asphalt can bubble and form sticky pools of tar
• The La Brea Tar Pits in L.A. are at least 38,000 years old
• These pools have trapped and preserved many different organisms,like the saber-toothed cats and dire wolves.
• From these fossils scientists have learned about what california was like 10,000 to 40,00 years ago
• Fossils in Peat
• Peat is the partly decomposed remains of plants
• Usually in swamps/bogs
• Not much oxygen in the lower layers
• Therefore,soft tissue has a chance to be preserved
• Peat is acidic and dissolves the hard minerals making them soft-softens the bony parts
• Fossils in Dry Air
• Since bacteria need moisture to grow and decay things
• Very dry air can also preserve things-mummification
• What can fossils tell us
• Fossils can show scientist 3 main things:
• The kind of organism that lived in the past
• How the environment has changed(ex:forest fossils found in Antarctica show the climate was much warmer in the past)

Diapositiva 2