Fossils and Geologic Time IT IS TIME TO ROCK!!!!!

How Old is the Earth? Before 18th Century – Earth = 6000 yo Based on Biblical Genealogies During 18th Century – Focus turned to Science 20th century Pierre and Marie Curie discovered radioactive decay – Lead to radioactive dating Using radioactive Decay – Earth = 4.6 Billion Years

Earth formed about 4.6 billion years ago. Chapter 14 The History of Life 14.1 Fossil Evidence of Change Land Environments Earth formed about 4.6 billion years ago. Gravity pulled the densest elements to the center of the planet. After about 500 million years, a solid crust formed on the surface.

14.1 Fossil Evidence of Change Chapter 14 The History of Life 14.1 Fossil Evidence of Change Atmosphere The gases that likely made up the atmosphere are those that were expelled by volcanoes. Water vapor (H2O) Carbon dioxide (CO2) Sulfur dioxide (SO2) Carbon monoxide (CO) Hydrogen sulfide (H2S) Hydrogen cyanide (HCN) Nitrogen (N2) Hydrogen (H2)

A fossil is any preserved evidence of an organism. Chapter 14 The History of Life 14.1 Fossil Evidence of Change Clues in Rocks A fossil is any preserved evidence of an organism. Most organisms decompose before they have a chance to become fossilized.

The History of Life

Nearly all fossils are formed in sedimentary rock. Chapter 14 The History of Life 14.1 Fossil Evidence of Change Fossil Formation Nearly all fossils are formed in sedimentary rock. The sediments build up until they cover the organism’s remains. Minerals replace the organic matter or fill the empty pore spaces of the organism.

Geologic Measure of Time: Relative Dating This Type of measure was created by Hutton, Steno, and Smith: Main idea is that the Earth, like an onion or ogre (apparently), is made of Layers. The further down the layer, the older it is. This is better known as Superposition.

Superposition

Absolute dating Absolute dating is based upon the fact that atoms of radioactive elements decay to form stable isotopes Important data about atoms: Atoms are the smallest particles of elements Atoms are composed Protons, Neutrons, and electrons Number of Protons = Atomic number

Absolute dating Not all atoms of the same element have the same number of neutrons in their nuclei; these variable forms are called isotopes

Radioactive Decay Radioactive Isotopes = Atoms that are unstable due to having too many neutrons -> Over time they lose Neutrons and Protons (decaying).

Radioactive Decay Half-Life: Amount of time required for 50% of original radioactive Material (Parent) to decay/convert into the new, lower energy form (daughter). -> Used to calculate ages

Absolute Dating Radioactive elements useful in absolute dating include: Uranium 235 (Lead 207) Half-life = 713 Million Years Potassium 40 (Argon 40) Half-life = 1.3 Billion Years Uranium 238 (Lead 206) Half-life = 4.5 Billion Years Rubidium 87 (Strontium 87) Half-life = 47 Billion Years Carbon-14 (Carbon 12) Half-life = 5700 Years

Absolute dating Radioactive Dating only useful on materials containing radioactive atoms.

The Geologic Time Scale Geologic Time Scale: graphical representation of the history of the Earth, divided into units based on geologic events Originally was based on Relative Dating only. Radioactive dating made the one we use today possible.

Major Extinctions Cretaceous–Paleogene extinction event 65 mya Death of the Dinos. Caused: Combo of Climate Change, Asteroid Impact, Volcanic Activity Triassic–Jurassic extinction event 199 mya to 214 mya 50+ % life wiped out. Allowing Dinos to dominate Caused: Combo of Climate Change, Asteroid Impact, Volcanic Activity Permian–Triassic extinction event 251 mya 96% of life wiped out. Cause: Massive volcanic eruption Late Devonian extinction 364 mya ~75% of life wiped out. Cause unknown. Ordovician–Silurian extinction events 439 mya 86% of life wiped out Cause: Ice Age, Lowering Sea Levels.