Chapter 4 A trip Through Geologic Time

4.1 FossilsKey Concepts

• How do fossils form?• What are the different kinds of fossils?• What does the fossil record tell about

organisims and environments of the past?

4.1 FossilsKey Terms

• Fossil• Sedimentary rock• Mould• Cast• Petrified fossil• Carbon film

• Trace fossil• Paleontologist• Scientific theory• Evolution• Extinct

4.1 FossilsHow Fossils Form

• Most fossils form when living things die and are buried by sediments.

• The sediments slowly harden into rock and preserve the shapes of the organisms.

• Fossils found in rock include molds an casts, petrified fossils, carbon films, and trace fossils

4.1 FossilsHow Fossils Form

• Molds and casts

4.1 FossilsHow Fossils Form

• Petrified fossils

4.1 FossilsHow Fossils Form

• Carbon films

4.1 FossilsHow Fossils Form

• Trace fossils

4.1 FossilsHow Fossils Form

• Preserved remains

4.2 The Relative Age of RocksKey Concepts

• What is the law of superpostions?• How do geologists determine the relative age

of rocks?• How are index fossils useful to geologists?

4.2 The Relative Age of RocksKey Terms

• Relative age• Absolute age• Law of superposition• Extrusion• Intrusion• Fault• Unconformity• Index fossil

4.2 The Relative Age of RocksThe Position of Rock Layers

• Law of Superposition –In horizontal sedimentary rock layers the oldest

layer is at the bottom.The layers get younger andthey get closer to the top.

4.2 The Relative Age of RocksDetermining Relative Age

• Clues from igneous rock – Extrusion - Layers where lava hardens on the

surface.Intrusion – When the magma hardened inside

the planet. It is always younger that the layers around it.

4.2 The Relative Age of RocksUsing Fossils to Date Rocks

• Index fossil is one that only appears in a specific layer of sediment.

4.3 Radioactive DatingKey Concepts

• What happens during radioactive decay?• What can be learned from radioactive dating?

4.3 Radioactive DatingKey Terms

• Atom• Element• Radioactive decay• Half-life

4.3 Radioactive DatingRadioactive Decay

• Atom –The smallest particle of an element.• Element – A type of matter in which all the

atoms are the same.During radioactive decay the atoms of one

element break down to form atoms of another element.

4.3 Radioactive DatingDetermining Absolute Ages

• Geologists use radioactive dating to determine the absolute ages of rocks.

Potassium-Argon DatingCarbon-14 DatingRadioactive Dating of Rock Layers

4.4 The Geologic Time ScaleKey Concepts

• Why is the geologic time scale used to show Earth’s history?

• What are the different units of the geologic time scale?

4.4 The Geologic Time ScaleKey Terms

• Geologic time scale• Era• Period

4.4 The Geologic Time ScaleThe Geologic Time Scale

• The age of the Earth is so huge that this Geologic Time Scale is used to put the span into sequence past to present.

• Era – The largest divisions (like seasons)Paleozoic – Mesozoic – Cenozoic

• Period – Divisions within Eras (like months)

4.4 The Geologic Time ScaleThe Geologic Time Scale

• Period – Divisions within Eras (like months)• ERA Paleozoic = Cambrian – Ordovician – Silurian – Devonian – Carboniferous - Permian

• ERA Mesozoic = Triassic – Jurassic - Cretaceous

• ERA Cenozoic = Tertiary - Quaternary

4.4 The Geologic Time ScaleThe Geologic Time Scale

4.5 Early EarthKey Concepts & Terms

• When did the Earth form?• How did Earth’s physical features develop

during Precambrian Time?• What were early Precambrian organisms like?

KEY TERMS• Comet• Continental Drift

4.5 Early EarthPlanet Forms

• Scientists hypothesize that Earth formed roughly 4.6 billion years ago.

4.5 Early EarthEarth Takes Shape

• Scientists believe that the planet began as a ball of dust, rock, and ice in space.

• Gravity pulled the mass together• More mass = more gravity = more mass = more

gravity until the area nearby was cleared.• The ball was struck repeatedly added mass and

kinetic energy heated up the mass.• (NOTE: Find a video link)

4.5 Early EarthEarth’s Surface Forms

• During the first several hundred million years of Precambrian Time, the atmosphere, oceans, and continents began to form.

4.6 Eras of Earth’s HistoryKey Concepts

• What were the major events in the Paleozoic Era?

• What were the major events in the Mesozoic Era?

• What were the major events in the Cenozioc Era>

4.6 Eras of Earth’s HistoryKey Terms

• Invertebrate• Vertebrate• Amphibian• Reptile• Mass extinction• Mammal

4.6 Eras of Earth’s HistoryThe Paleozoic Era

• The Cambrian Explosion• Vertebrates arise• Life Reaches Land• The Carboniferous Period• Mass extinction ends the Paleozoic• The Supercontinent Pangaea

4.6 Eras of Earth’s HistoryPrecambrian

4.6 Eras of Earth’s HistoryCambrian Period

4.6 Eras of Earth’s HistoryOrdovician Period

4.6 Eras of Earth’s HistorySilurian Period

4.6 Eras of Earth’s HistoryDevonian Period

4.6 Eras of Earth’s HistoryCaboniferous Period

4.6 Eras of Earth’s HistoryPermian Period

4.6 Eras of Earth’s HistoryTriassic Period

4.6 Eras of Earth’s HistoryJurassic Period

4.6 Eras of Earth’s HistoryCreataceous Period

4.6 Eras of Earth’s HistoryTertiary Period

4.6 Eras of Earth’s HistoryQuaternary Period