FOSSILS

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?

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

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.

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.”

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.

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.

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.

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.

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.

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.

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

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

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.

Pop Quiz What is a fossil? What are 5 different ways fossils can form? 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