Fossils Fossils are found in Sedimentary rocks They help provide information of life forms that lived thousands of years ago.

Types of Fossils Petrified – Minerals have filled in where an organisms once was Molds – A hollow area that an organism has left. Cast – A copy of the shape of the organism (opposite of a mold) Carbon Film – a thin coating of carbon that is left behind when gases have been release by the decaying fossil (like a leaf print on a rock) Trace – An imprint that an organism left behind (like a footprint)

Bones A fossil bone should have different canals and webbed structure of the bone. You can even try a tongue test. The porous nature of some fossil bones will cause it to slightly stick to your tongue if you lick it, though you might want to have a glass of water handy if you feel compelled to try this. 

Petrified Fossils Fossils in which minerals replace all or part of an organism. How does this happen? Water rich in dissolved minerals seeped into spaces, evaporated, leaving the hardened minerals behind. Example – petrified wood

Molds and casts Most common type of fossil. Both copy the shape of the organism. A mold is a hollow area of sediment in the shape of the organism. A cast is a copy of the shape of an organism.

Carbon Films Carbon film is an extremely thin coating of carbon How does this happen? All organisms are made of carbon. When they are buried, the materials that make up the organism evaporates. These gases escape leaving carbon behind.

Trace Fossils Trace fossils provide evidence of the activities of ancient organisms. Examples A footprint provide clues about the size and behavior, the speed, how many legs it walked on, lived alone or with others. A trail or burrow can give clues about the size and shape of the organism, where it lived, and how it obtained food.

How old is it? Relative Age – It’s age when compared to others ( I am older than you) Absolute age – It’s actual or real age We use radioactive dating to find this Unconformity – a gap in the the geological record (like from erosion)

Laws of Geologic History

Law of Superposition The oldest layer is at the bottom and the youngest layer is at the top.

Law of Crosscutting - In a series of horizontal sedimentary beds, if there is an inclusion which cuts vertically through them, it must be younger than the sediment beds.

Law of Inclusions - The intruding rock (Rock A) must have been there first to provide the fragments in the younger rock (Rock B)