FOSSILS

1. FOSSILS

2. Think About It . . . • Can you name any dinosaurs? • Do you know what they looked like or how they moved? • Scientists have been able to tell us many things about organisms (such as dinosaurs) that lived millions of years ago. • How do scientists learn about these organisms if they’ve never seen them?

3. Fossils! • Fossils = the remains or imprints of an organism that lived long ago. • Fossils can be formed in five different ways. . .

4. 1) Fossils in Rocks • 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 become fossils when the sediment hardens to form a sedimentary rock.

5. 2) Fossils 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.”

6. 3) Frozen Fossils • Ice and cold temperatures slow down decay. • Fossils can be preserved in blocks of ice. • Fossils of woolly mammoths, relatives of elephants that went extinct 10,000 years ago, have been found in ice.

7. 4) Petrification • 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.

8. 5) 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 & dire wolves. • From these fossils scientists have learned about what California was like 10,000 to 40,000 years ago.

9. Trace Fossils • Organisms can leave behind clues about their lives that are also fossils. • These clues were made by an organism, but they do not include parts of the organism’s body. • This is called a trace fossil. • For example, fossils of footprints / tracks tell scientists how big the animals was and how fast it moved.

10. Other Examples of Trace Fossils • Burrows (shelters made by animals that bury themselves in the sediment) may be filled with sediment and preserved. • “Caprolites” = dung (“poop”) that is fossilized.

11. Molds & Casts • Mold = the print/impression left in sediment/rock where the plant/animal was buried. • Cast = forms when sediment fills a mold and becomes rock. • Both can show what the inside or outside of an organism looked like.

12. What Can Fossils Tell Us? • Fossils can show scientists 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) • How organisms have changed

13. How Old Is It? • To understand the history of the Earth, scientists have put fossils in order based on their ages. • They use relative dating and absolute dating methods

14. Index Fossils • Fossils of certain types of organisms can be found all over the world. • But these fossils are found only in rock layers of a certain age. • These are called index fossils. • When scientists see a specific index fossil, they know right away how old it is • Ex: When scientists find Phacops in a rock layer, they know the rock layer is 400 million yrs old.

15. Pop Quiz • What is a fossil? • The remains or imprints of an organism that lived long ago. • What are 5 different ways fossils can form? • In rock, amber, ice, asphalt, or by petrifaction • What 3 things can fossils tell us? • The kind of organism that lived in the past • How the environment has changed • How organisms have changed