How to tell time with rocks Fossils How to tell time with rocks

Looking at Fossils A fossil is any naturally preserved evidence of life.

Mineralization / Petrification Fossil Organisms can also be preserved by mineralization (petrified), a process in which minerals fill in pore spaces of an organism’s tissues.

Fossils in Amber When tree sap hardens, an insect may be preserved inside. Hardened tree sap is called amber. Some of our best insect fossils are found in amber.

Mummification When organisms die in dry places (such as deserts), they can sometimes dry out so fast that there isn’t enough time for their soft parts to decay.

Frozen Fossils Frozen specimens Found in ancient glaciers.

Trace Fossils Any naturally preserved evidence of an animal’s activity is called a trace fossil.

Molds and Casts A mold is a cavity in the ground or rock where a plant or animal was buried. A cast is an object created when sediment fills a mold and becomes rock.

Fossils Show Changes in Environments Fossils can reveal changes that have occurred in parts of the Earth. How did sea creatures end up on dry land?

Fossils Show Changes in Life Older rock layers contain organisms different from those found in younger rock layers. Life forms have changed over millions of years. For example, giant sea reptiles came before giant land dinosaurs. Mammals arrived last!

47) A fossil is a remnant or trace of an organism from the past, such as a skeleton or leaf imprint.

48) Fossils are embedded and preserved in the earth's crust.

49) A Trace Fossil is a fossil of a footprint, trail, burrow, or other trace of an animal rather than of the animal itself

 50) A footprint of an ancient animal in a rock is called a trace fossil.

51) Large animals occasionally became trapped in tar and become a fossil.

52) Fossils, the remains of organisms preserved in sedimentary rocks, are part of the evidence scientists use to infer changing conditions at the Earth’s surface through time.

53) Oil and Natural Gas are formed from ocean plankton that died millions of years ago.

54) Coal, Natural Gas, and Oil are all examples of fossil fuels.

55) Petrified wood is a fossil.   56) Petrified wood forms when water with natural minerals slowly fills the pores of wood. Over thousands of years the wood slowly decomposes leaving behind the minerals from the water. The minerals harden and form a rock that looks exactly like the original wood.

 57) How much wood is actually located in petrified wood? 0%.

58) The geologic column is how geologists have organized the entire history of the Earth in chronological order.

ROCKS TELL A STORY Rocks can tell where they were made and when Sedimentary rocks can have fossils in them Rocks can tell when mass extinctions happened STUDY AND COMPARISON OF ROCK LAYERS OR STRATA IN THE 19TH CENTURY LED SCIENTISTS TO BELIEV THAT A CORRELATION EXISTS BETWEEN PLACE AND TYPE OF ROCK 24

LAW OF SUPERPOSITION For undisturbed rocks, the oldest layer is on the bottom and the youngest is on top (Supai is oldest) 25

59) Superposition states that older layers of rock are below younger layers of rock.

LAW OF SUCCESSION Fossils are found in a predictable sequence Fossils in rock B are older then fossils in rock A 27

RELATIVE DATING & AGE Relative Dating: putting rocks and geological events in correct chronological order Relative Age: how old something is in comparison to something else HOW? Use of sedimentary rocks Use of fossils Study of strata 31

Absolute Dating Absolute dating is a process that establishes the precise age of an object, fossil, or rock layer by determining the number of years it has existed. Radiometric dating is how absolute dating is accomplished. Scientists determine the actual age of a fossil or rock by measuring the decay of certain atoms.

60) Radiometric dating is how geologists determine the age of rocks by measuring the decay of atoms.

61) Radiometric dating is the most accurate way to date rocks and fossils.

What kind of rocks are these fossils in? Which layer is oldest? Which layer is youngest? How do you know? 35