Aging the Earth

a. Using the Fossil Record b. Using the Law of Superposition c. Using Relative Dating d. Using Absolute Dating through Radioactive Decay

a. Fossils form when: i. Living things die and are buried under sediment ii. As the sediment hardens and turns to sedimentary rock it preserves the shape of the organism iii. When the organism dies other living things eat the soft part of the animal or the soft part decays over time iv. The hard bones and structures of the organism are left behind to form a fossil

b. Types of Fossils i. Mold and Cast: 1. This is when a hollow area in sediment forms from an organism that was once there 2. Water brings in minerals and sediment that fills in the mold creating a cast (a solid copy of the shape of the organism) 3. Preserve the fine details

ii. Petrified Fossils: 1. Petrified means “Turned to Stone” 2. Minerals replace all or part of the organism 3. Water seeps into the space between the cells and when the water evaports it leaves behind the minerals 4. Examples:

iii. Carbon Films: 1. An extremely thin coating of carbon on a rock 2. This preserves delicate plants and insects 3. Many times these look like a drawing

iv. Trace Fossils: 1. Shows activity of ancient organisms 2. These prints get covered in sediment and turn to rock, leaving the imprint in the rock 3. Example: foot prints, trails and burrows

v. Preserved Remains: 1. Entire Organisms are preserved 2. Some get stuck in tree sap which becomes amber 3. Some are frozen in ice which can even preserve the hair of an animal

c. The Fossil Record is a group of fossils that shows the history of living things i. This is studied and created by Paleontologists d. This record can tell us about climate and environmental differences throughout the Earths History e. It can show us how organisms have changed over time f. The record can also show us how extinct animals may have looked

a. Index fossils: used to help give a relative age to the rock in which it was found. b. Which rocks are the same age?

a. Uses radioactive elements to try and find how old a rock is b. Radioactive Decay i. These radioactive elements begin to break down and form another element ii. Each radioactive element has a different rate of decay c. A Half-Life is the time in which it takes for half the radioactive element to decay

d. These radioactive elements occur naturally in Igneous Rock e. Over time, the Igneous Rock begins to change due to Radioactive Decay i. The Radioactive Element amount begins to decrease ii. The New Element amount begins to increase

f. Scientists use this to find the Absolute Age of a rock i. They use the half-life to determine how much of the Radioactive element has decayed ii. They then calculate how old the rock is

g. Two Types of Radioactive Dating i. Potassium-Argon Dating 1. Potassium (a radioactive element) turns to the stable Argon element. 2. Believed to have a half-life of 1.3 billion years 3. Used in dating the most ancient rocks and fossils

ii. Carbon-14 Dating 1. Found in almost all plants and animals 2. Carbon-14 (the radioactive element) turns to Nitrogen (the stable element) 3. Carbon-14 has a half-life of 5,730 years 4. Only used to date rocks younger than 50,000 years old 5. Also not used often because very little rock contains Carbon-14

h. Example: i. You know that Element 1, which is a radioactive element, turns into Element 2, a stable element. You also know it take 5 Years for Half of Element 1 to turn to Element What is the half-life of Element 1 2. If you find a rock that is made up of 50% Element 1 and 50 % Element 2, how old is this rock? 3. If you find a rock that is made of 25% Element 1 and 75% Element 2, how old is this Rock? 4. How many half-lives old is the second rock you found?

i. Radioactive Dating is used to find the Earth’s Age i. They take rock samples from all over the earths crust to get a picture of how old the rocks are on the earth

a. By using Radioactive Dating and using the Fossil Record scientist have created the Geological Time Scale b. The Geological Time Scale is our best guess as to how old the earth is and what animals existed throughout earth history. c. This also includes evidence of Natural Disasters that may have occurred to change the earth in some fashion i. Could have changed the environment, the climate, the animals that are on the earth.

d. Split into Eras, Periods, and Years. e. Scientists split this into 3 separate eras i. Each era is split into multiple periods

f. 3 Different Era’s i. Paleozoic Era: life flourished and grew during this time period ii. Mesozoic Era: “Age of the Dinosaurs” iii. Cenozoic Era: Earth began to rebuild itself and the new environment began to form

g. Important time Periods i. Triassic Period (Mesozoic Era): Dinosaurs began to take over the earth ii. Cretaceous Period (Mesozoic Era): Large Extinction event that wiped out the dinosaurs iii. Paleogene Period (Cenozoic Era): earth began to cool and the climate changed allowing for new and different growth.