Paleontology and Fossils images.usatoday.com/.../2006/11/07/fossil472.jpg

Uni-form-i-ta-rian-ism  In 1798, James Hutton, published the Theory of the Earth.  He said that the Earth’s geologic processes, that shaped the Earth, have been working together to continue reshaping the Earth.  This principle is called Uniformitarianism

Ca-ta-stro-phism  Catastrophism is the belief that all geologic change occurs suddenly.  These scientists believed that catastrophes (earthquakes, floods, hurricanes, etc.) caused the Earth to change.

Which Theory is Correct?  Scientists now believe that both processes shape the Earth!  It is believed that some catastrophes do change the Earth. For example, an Asteroid hit the Earth and caused extinction of Dinosaurs.

How Do Scientists Know about the Earth?  Studying layers of the Earth explains our history. (stratification!)  Scientists use 2 types of Dating:  Relative Dating is determining whether an object is older or younger than another by using comparison.  Absolute Dating is determining the exact age of an object by using a number of years.

Dating – A Measure of Time  Which statement describes Relative or Absolute age? 1.She is 12 years old. ______________ 2.She is my younger sister. _____________ 3.The 75 foot oak tree is older than the 12 foot oak tree. _________________. 4.The man is older than the teenager. _______________

 Write a short paragraph explaining why geologists use both absolute and relative dating to interpret the past.(pg st 2 paragraphs, pg st paragraph)  __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________ __________________________________

Relative Dating  Superposition is a principle that states younger rocks lie above older rocks.  “Law of Superposition”

Law of Superposition By applying this law scientists know that layer A is older than Layer C. Layer C is younger that Layer B. Which layer is the youngest? ______

Challenges  Natural Forces cause older layers to be pushed above younger layers and makes it hard to distinguish between older and younger.  They have used rock layers from all around the world to create a geologic column.

Geologic Column  The geologic column is a sequence of rock layers that contains all the known fossils and rock formations on Earth arranged from oldest to youngest.  View geologic column: The column The columnThe column

4 Disturbances  Natural forces are disturbances that cause changes in rock layers. (pg. 139)  All Disturbances are younger than the rock around them.  Faults  Intrusions  Folding  Tilting

Disturbances continued  Geologists use features that cut across existing rock to help determine the rock’s relative age.  Faults are breaks in the Earth’s crust where breaks slide.  When molten rock squeezes into existing rock and cools it is called an intrusion.

Disturbances continued  Folding occurs when rock layers bend and buckle from Earth’s internal forces.  Tilting occurs when internal forces slant rock layers without folding them.  These events are always younger than the rock layers that they affect.

Formation of Unconformities  When layers of rock are missing in sequence we call this unconformity.  Erosion and nondeposition have a lot to do with wearing away rock and causing unconformity.  Where does this rock go?

Types of Unconformities (pg. 141)  Unconformities link: Unconformities Unconformities  Disconformity – part of a parallel rock layer is missing. Most common.  Nonconformity – sedimentary rock layers lie on top of eroded igneous or metamorphic rock.  Angular unconformity – appears between horizontal layers that are tilted or folded.

Absolute Dating  To determine the actual age of rocks and fossil scientists use a process called absolute dating.  To do this they need to analyze radioactive isotopes.  Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

Isotopes  Most isotopes are stable.  Unstable ones are called radioactive.  Radioactive isotopes tend to break down into stable isotopes over a period of time called radioactive decay.  This breakdown happens at a steady pace and scientists use the relative amounts of stable and unstable isotopes to determine the object’s age.

How Does Radioactive Decay Work?  Link: Radiometric Dating Radiometric DatingRadiometric Dating  Determining the ratio of parent material to daughter material.  Link: Half-life Half-life  For every half-life, the parent material decreases by one-half.

Types of Radiometric Dating  Uranium-238 (has the longest half-life)  Potassium-40  Carbon-14 (Used to determine the most accurate and precise age of the Earth)

Fossils FFFFossils are preserved remains or traces of living things. LLLLiving things die and are buried by sediments. SSSSediments slowly harden into sedimentary rock. AAAA paleontologist is a scientist who studies fossils.

Types of Fossils  Preserved Remains – fossils found in tar, amber, or frozen. Even hair/teeth are preserved! Saber Tooth Cat!  Petrified fossils – minerals replace all or part of an organism.  Petrification occurs to wood when water, rich in dissolved minerals, seeped into plant cells and then evaporated leaving hardened minerals behind.  Molds and casts – Most common. Copy of the shape of the organism.

Fossils Found in Rock Molds and casts

Fossils Found in Rock  Carbon films – thin film of carbon is left from a living organism. This can occur as an organism decays and gases are released, only carbon is left behind. Carbon film

Fossils Found in Rock  A mold is a hollow area in sediment in the shape of an organism or part of an organism.  A cast is a copy of the shape of an organism. When an animal’s footprint fills with sediment and turns to rock.

Trace Fossils  Trace fossils are fossils that provide evidence of the activities of ancient organisms:  Footprints  Nests  Burrows – a shelter made by an animal that dug into the ground.

Change over time  Together, all of the information that paleontologists have gathered about past life is called the fossil record.  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.

Change over time  Older rocks contain fossils of simpler organisms while younger rocks contain fossils of more complex organisms.  Evolution is the gradual change in living things over long periods of time.

Geological Time Scale  How old is the Earth? Approximately 4.6 billion years old.  The time scale was developed by studying rock layers and index fossils worldwide.  Placed layers by relative ages, then used absolute dating to refine the scale.

Geological Time Scale  Basic units of geologic time scale are:  Eons  Eras  Periods  Epoch

Geological Time Scale  Eons – the largest division of time.  Eras – second largest division.  Periods – Periods are divided into epochs  Epochs - smallest

Eons  Hadean eon – found meteorites and rocks from the moon.  Archean eon – found earliest know rocks on Earth  Proterozioc eon – first organisms with well-developed cells appeared.

Eras  Paleozoic Era – first land-dwellers, plants and amphibians.  Mesozoic Era – Age of the reptiles  Cenozoic era – Age of Mammals