Chapter 8

Fossil - the preserved remains or traces of a living thing. Mold - the hollow space that is left. Cast - forms when dissolved minerals fill the space and harden. Index fossil- helps scientists find the age of a rock layer that may be out of order. Theory -

 One theory is that 4.5 billion years ago Earth formed from a giant cloud of gas and dust.  Another theory says that 3.5 billion years ago the first organism or living thing appeared.  The organisms reproduced by dividing  Fossils show how organisms have changed over time.  Most fossils form in sedimentary rocks.

 Continental drift is the theory that the continents have been slowly drifting apart for millions of years.  225 million years ago all of Earth’s landmasses were joined.  This landmass is now called Pangea.  It then broke into pieces- Earth’s continents.

 When organisms die, they usually are eaten or decay quickly.  Some remains are buried in sediment, ice, or tree sap.  These remains become fossils.  Some fossils are the actual hard parts of organisms.  Teeth, bones, shells  Some organisms or parts become petrified.

 Mold is the hollow space that is left.  Cast forms when dissolved minerals fill the space and harden.  Mold and casts preserve the shapes of organisms.  Sometimes an entire animal is preserved  Example- Insects have been trapped in tree sap or mammoths buried in ice and snow.

 Trace fossils are evidence of an animal’s activities.  A carbon film is an extremely thin coating of carbon.  Fossils tell scientists what these past organisms were like.

 Sedimentary rock forms in layers.  The relative age of a rock is its age compared with the ages of other rocks.  This process would work if the rock layer was never disturbed.  It is disturbed from earthquakes, water, and wind.

 Index fossils provide a way to match rocks of the same age found in different places.  The age of a rock in years is its absolute age.

 Paleontology- The study of fossils.

 Some types of organisms haven’t changed much through years, but many others are extinct.  Fossils show what living things were like in the past and how they have changed.

 The study of fossils  They compare fossils with organisms living today.  They study ways living things have changed.

ELEPHANTMAMMOTH

 Many plants die and decay without a trace and don’t leave a fossil.  Because they have no hard parts such as bones or shells.  Most plant fossils that we do have are carbon films.  An object is petrified when dead cells are replaced by minerals.  The first plants lived in the sea.  Ferns were the main type of plants for more than 175 million years.  Plant fossils provide clues about past environments.  Can infer the climate that existed on Earth millions of years ago.