History of Earth and its landforms… 8.E.2.1 and 8.E.2.2 Create a brainsplash in your notebook for the term “Fossil”.

What is a fossil? Fossil: preserved remains or traces of an organism that lived in a past life – Give clues to… the diversity of living things over the history of the Earth Past climate and surface changes on Earth Changes that have occurred within organisms over time

What are the different types of fossils? Types of fossils are based on how they were formed. Formation process varies depending on where and under what environmental conditions Mold Fossil – Sediments bury an organism and change into rock – Organism decays leaving a cavity in the shape of an organism

Cast Fossil – Forms when a mold is filled with sand or mud that hardens into the shape of the organism Petrified fossil – Minerals soak into the buried remains, replacing the remains, and changing them into rock

Preserved Fossil – Entire organism or parts of organisms are prevented from decaying by being trapped in rock, ice, tar, or amber Carbonized Fossil – Forms when organisms or parts, like leaves, stems, flowers, fish are pressed between layers of soft mud or clay – Mud/clay hardens, squeezing almost all of the decaying organism away, leaving the carbon imprint on the rock

Trace Fossils – Form when mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind Mr. Parr- Fossils

What are the different types of rock? Sedimentary rock: rock formed by deposition of sand, clay and other pieces of rock that are compacted together under pressure Metamorphic Rock: formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). Igneous Rock: formed when magma (molten rock deep within the earth) cools and hardens.

What is the fossil record? Millions of fossils have been collected and studied Fossil Record- the complete body of fossils that shows how species and ecosystems change over time – Extinction – How new life forms appeared – Certain organisms could only live in specific environments or under particular climate conditions

What is relative age? The age of one object compared to the age of another object Does not tell exact age Relative age of rocks and fossils can be determined two ways: – Ordering of rock layers – Index fossils

What is the law of superposition? Each layer of rock is deposited on top of other layers Law of Superposition: oldest rocks lie on the bottom, youngest rocks lie on the top of an undisturbed sequence of sedimentary rock – Used to read rock layers The Law of Superposition- Grand Canyon

How do scientists use the ordering of rock layers for relative dating? Scientists infer that the relative age of the rock or fossil in the rock is older if farther down in rock layers Relative dating is best when the rock layers have been preserved in their original sequence – Tectonic plate motion can distort the layers – Youngest layers are not always found on top

What are index fossils? Index Fossils – Organism must have lived during a short part of Earth’s history – Many fossils of the organism must be found in rock layers – Must be found over a wide area of earth – Organism must be unique The shorter time period a species lived, the better an index it is. Can be used to find the relative age of rock layers

What are trilobites? A group of hard-shelled animals whose body had three sections TrilobitesTrilobites – Lived in shallow seas – Became extinct about 245 million years ago Key example of index fossil – If a trilobite is found in a rock layer, it can be compared to trilobites found in other rock layers to estimates the age of the rock layer in which it was found.

What is radioactive decay? Universe if full of naturally occurring radioactive elements – Radioactive decay- unstable atoms breakdown over time into stable isotopes or other elements Molten Rock cools, trapping radioactive atoms inside. Radioactive atoms always break down at the same rate and into the same other form

What is half-life? The rate of change of a radioactive element if measured in half-lives. – Half-life: the length of time it takes for half of the atoms in a sample of a radioactive element to change from an unstable form to another form.

What is radiometric dating? Scientists measure the quantity of unstable atoms in rock and compare to stable quantities. Elements with half-lives of millions to billions of years are used to date rocks. – Uranium 235 has a half life of 704 millions years. It changes to lead 207. – Carbon 14 is used to date remains of things that were once alive. Half-life: 5730 years Absolute dating – scientists find an absolute age of the rock because they know the rate at which the radioactive elements decay

What is the geologic time scale? Divides earth’s history into intervals of time defined by major events or changes on Earth Earth is 4.6 billion years old – Eon: largest unit of time, 4 Eons in Earth’s history – Era: Eons are divided into eras – Period: eras are subdivided into periods – Epoch: periods of 2 eras are further divided into epochs

What are the “eras” on the geologic time scale? At the end of each era, a mass extinction occurred. Precambrian era – Creation of earth- 4.6 BYA – Major events Formation of the sun and light Creation of earth Creation of the atmosphere through volcanic out-gassing Creation of oceans Creation of life – Began with simple life forms: bacteria and algae – Rise of simple organisms (jellyfish, sea worms) by the end of the era – Few fossils because of soft bodied organisms

Paleozoic Era – Began with early invertebrates  vertebrate fish  arachnids and insects  amphibians  reptile – Early land plants (mosses, ferns) – End of era- seed plants – Mass extinction cause most marine invertebrates and amphibians to disappear.

Mesozoic Era – Reptiles were dominant, dinosaurs – Small mammals and birds appeared – Flowering plants, and other mammals appeared towards the end of the era – Mass extinction caused dinosaurs to become extinct

Cenozoic Era – New mammals appeared, others became extinct – Diversity of life increased – Flowering plants became more common – Humans are part of the most recent period

What are ice cores? Cylinders of ice that are drilled out of glaciers and polar ice sheets Help to understand how climate has changed – Snow falls and carries compounds that are in the air with it – In areas where the temperature is rarely above freezing, layers of ice build up – In the layers is record of the atmosphere at that time

How are sedimentary rocks used to determine geological history? 75% of the rocks on Earth’s surface Studying the contents give us information Igneous rock can disturb sedimentary rock – Molten rock forces its way up through the layers above it – Forms younger igneous rock layers within and across sedimentary layers

What is a fault? A break in the rocks that make up the Earth’s crust that is formed due to the movement of rock on either side of the fault. Occur when there is a movement of tectonic plates – Earthquakes Dip Slip Fault: land changes their vertical position Strike Slip Fault: land changes their horizontal position

What is the Theory of Plate Tectonics? Earth’s continental and oceanic plates continually change the shape of Earth’s crust throughout time. Using the theory, scientists can study and predict geologic events. Evolution of Earth’s living things is strongly linked to the movements of Earth’s plates.

Additional Information Absolute (radioactive) Dating Measurement of the known rates of decay of radioactive materials that an object contains in order to determine the age of the object Index Fossils Fossil known to have lived in a particular geologic age that can be used to determine the date of the rock layer in which it was found Law of Superposition Law that states that in undisturbed rock layers that newer layers will be deposited over older layers Relative Dating Determining the age or order of things from the past or past events without knowing or calculating the actual age Sedimentary rock Rock formed by deposition of sand, clay and other pieces of rock that are compacted together under pressure Uranium Radioactive heavy metal that is an abundant source of nuclear energy that has 14 known isotopes used in radioactive dating