Geology: History of Earth
LEQ: How do fossils tell how organisms have changed over time?
Section 1: Fossils
~ Most fossils form when living things die and are buried by sediments. The sediments slowly harden into rock and preserve the shapes of organisms.
Vocabulary
~ Paleontologists: Scientists who study fossils.
~ Sedimentary Rock: The type of rock that is � made of hardened sediment cemented and compacted together.
2. Kinds of Fossils
Petrified Fossils
~ Fossils in which minerals replace all or part of an organism.
Petrified means “turning into stone.”
Molds and Casts
Mold: a hollow area in sediment in the shape of an organism or part of an orgaism.
~ form when a hard part of the organism is � buried in sediment.
Cast: a copy of the shape of an organism by dissolved minerals.
~ A cast is the opposite of its mold.
Carbon Films
An extremely thin coating of carbon on rock preserving the delicate parts of plant leaves and insects.
Trace Fossils
Provide evidence of the activities of ancient organisms.
Ex. a fossilized footprint of a dinosaur is a trace fossil.
Preserved Remains
Some processes preserve the remains of organisms with little or no change.
~ Tar
~ Amber
~ Freezing
3. Change Over Time
~ Paleontologists collect sedimentary rocks from all over the world to gather information to determine what past life forms were like, what they ate, what ate them, and their environment.
~ The fossil record provides evidence about the history of life on Earth. The fossil record also shows that different groups of organisms have changed over time.
4. Fossils and Past Environments
~ Fossils found in an area tell whether the area was a shallow bay, an ocean bottom, or fresh-water swamp.
~ Fossils provide evidence of Earth’s climate in the past.
~ Scientists can use fossils to learn about changes in Earth’s surface.
Theory of Evolution
Fossil record provides evidence that supports evolution-the gradual change in living things over long periods of time.
A scientific theory is a well tested concept that explains a wide range of observations.
Chapter 4 Section 1 Review:
LEQ: How are index fossils used to determine the relative age of rocks?
Relative age: its age compared to the ages of other rocks.
Absolute age:the number of years since the rock formed.
2. The Law of Superposition
In horizontal sedimentary rock layers, the oldest layer is at the bottom. Each higher layer is younger than the layers below it.
-used to determine the relative age of rock
3. Other Clues to Relative Age
Geologist find some of these clues by studying extrusions and intrusions of igneous rock and faults.
Extrusiones From Igneous Rock
Lava that hardens on the surface.
-rocks layers below an extrusion are always older than the extrusion
Intrusion
~ Magma that cools and hardens into a mass of igneous rock below the surface of Earth.
-An intrusion is always younger than the rocks layers around it or below it.
Clues in Faults
A break in Earth’s crust.
A fault is always younger than the rock it cuts through.
Movement along faults can make it harder for geologists to determine the relative age of rock layers.
4. Gaps in the Geologic Record
The geologic record of sedimentary rock is not always complete.
Deposition and Erosion are constantly changing Earth.
~ Unconformity: a gap in the geologic record.
~ Shows where rock layers have been lost to erosion.
5. Using Fossils to Date Rocks
~ Index fossil: widely distributed and represents a type of organism that existed only briefly.
widely distributed = occurs in different areas
Index Fossils used to match rock layers
~ Index fossils tell relative ages of rock layers in which they occur.
Chapter 4 Section 2 Review
LEQ: What is the importance of radioactive dating?
Section 3: Radioactive Dating
~ Atom: the smallest particle of an element.
~ Element: all the atoms of a particular type of matter are the same
The atoms of one unstable element breakdown to form atoms of another element.
~ occurs naturally in igneous rocks using the rate of decay to determine the rock’s age
Radioactive Decay
2. The Rate of Radioactive Decay
The rate of decay of each radioactive element is constant -it never changes.
~Half-life: the time it takes for half of the radioactive atoms of a radioactive element to decay.
3. Absolute Ages From Radioactive Dating
~ Geologists use radioactive dating to determine the absolute ages of rocks.
Potassium-40 Dating
Scientists often date ancient rocks using potassium-40 due to its long half-life=1.3 billion years.
Carbon-14 Dating
~ All plants and animals contain carbon.
~ After an organism dies, no more carbon is added, and the carbon-14 begins to decay at a half-life of 5730 years.
~ Scientists measure the amount of carbon-14 left to determine the absolute age.
~ This cannot be used to date really ancient fossils.
4. Radioactive Dating of Rock Layers
~ Radioactive dating does provide the age of the particles,but not the age of the sedimentary rock.
~ Scientists use radioactive dating for the igneous intrusions and extrusions near the sedimentary rock layers.
5. How Old is Earth?
~ Radioactive dating shows that the oldest moon rocks are about 4.6 billion years old. Scientists infer that Earth is only a little older than those moon rocks -roughly 4.6 billion years old.
Chapter 4 Section 3 Review
LEQ: How is the geologic time scale used to show Earth’s history?
Section 4: The Geologic Time Scale
~ Because the time span of Earth’s past is so great, the Geologic time scale to record the life forms and geologic events in Earth’s history.
2. Divisions of Geologic Time
~ The Precambrian Time lasted from 544 my to 4.6 by ago (88% of Earth’s history). After this time, longer units called eras occurred.
3. Eras, Periods, and Epochs
Eras: One of three long units of geologic time between the Precambrian and the present.
~ The Paleozoic Era, the Mesozoic Era, � and the Cenozoic Era.
Era
Paleo -means “ancient or early”
Meso -means “middle”
Ceno -means “recent”
zoic- means “life”
Periods
~ One of the units of geologic time into which geologists divide eras.
Epochs
~ Subdivisions of the periods of the geologic time scale are used to help build a more complete fossil record.
Chapter 4 Section 4 Review
LEQ: What were the major events in Earth’s geologic history?
Section 5: Earth’s History
~ Precambrian Earth:
Earth formed from a mass of dust and gas � about 4.6 billion years ago.
~ The Earliest Forms of Life:
Scientists infer that single-celled organisms in �rocks that formed about 3.5 billion years ago. Organisms first began photosynthesis about 2.5 billion years ago.
2. The Paleozoic Era
Life Explodes:
~ At the beginning of this era, a � great number of different kinds of � organisms evolved-Cambrian Explosion.
~Invertebrates lived in the sea.
During the Ordovician and Silurian Periods, jawless fishes evolved being the first vertebrates-with a backbone.
3. Life Reached Land
By the Silurian and Devonian (Age of the Fishes) Periods, plants and animals began to invade the land.
-Amphibian: an animal that lives part of its life on land and part of its life in water.
Carboniferous Period: reptiles, insects, cone-bearing plants and trees
Reptile: a vertebrate with scaly skin and lays eggs with tough, leathery shells.
4. Mass Extinction Ends the Paleozoic
Mass extinction: when many types of living things become extinct at the same time.
~Scientists do not know what caused the mass extinction (maybe a climate change), but as much as 95 percent of the life in the oceans disappeared.
-Trilobites and many amphibians became extinct.
5. The Supercontinent Pangaea
~ During the Permian period, about 260 million years ago, Earth’s continents moved together to form a great landmass, or supercontinent, called Pangaea.
6. The Mesozoic Era
The Triassic Period
~ Reptiles were so successful during the � mesozoic Era that this time is often called � the Age of Reptiles.
~ Mammals- warm-blooded vertebrates that feed their young milk appeared during this time. The first dinosaurs appeared.
The Jurassic Period
-Dinosaurs became the dominant� animal on the land for about 150 million � years.
-First birds appeared.
Mesozoic Era
The Cretaceous Period
~ Reptiles were still dominant vertebrates � and dinosaurs ruled the land, but mammals continued to evolve.
~ Flying reptiles became extinct.
~ Flowering plants evolved, bearing fruits � to help their seeds survive.
At the close of the Cretaceous Period, about 65 million years ago, another mass extinction occurred. Scientists hypothesize an object from space struck Earth or climate changed due to increased volcanic activity. No dinosaurs survived, over half plant and animal groups and many reptiles became extinct.
Another Mass Extinction
7. The Cenozoic Era
The extinction of dinosaurs created an opportunity for mammals. During the Cenozoic Era, mammals evolved adaptations that allowed them to live in many different environments -on land, in water, and even in the air.
The Tertiary Period
~ Earth’s climates were generally warm and mild.
~ Mollusks appeared and marine mammals evolved.
~ Flowering plants, insects and mammals on land flourished. Some mammals became very large.
The Quaternary Period
Earth’s climate cooled in the ice ages.
~Repeatedly, thick continental glaciers advanced and retreated over parts of Europe and North America.
~ Human ancestors appeared 3.5 million years ago with homo sapiens evolving as early as 100,000 years ago.
Chapter 4 Section 5 Review