Chapter 2: Geological Time Flashcards
Describe the basic steps of fossil formation.
Stage 1: An animal dies and the skeleton is buried by sediment
Stage 2: The sediment gets thicker and compacts, turning layers into hard rock
Stage 3: The skeleton dissolves, leaving a cavity (hole), and a mould of the shape of the skeleton is formed
Stage 4: Water rich in minerals fill the cavity. The minerals crystallise inside the mould and a cast is formed.
Stage 5: Millions of years later, the rock rises to Earth’s surface. Erosion occurs and the fossil is exposed, waiting to be discovered.
Compare casts and moulds.
A cast forms when an organism in rock decomposes and the space in the rock fills with soil and turns to rock. A 3D model of what the organisms looked like in life and therefore a positive image while a mould is a negative image as it is usually an imprint left in the rock showing the outside of an organism.
Identify some famous fossil sites and some of the fossils for which they are famous.
Messel Pit: The most famous fossil from Messel is Ida, a primate from 47 million years ago
Ediacara, Flinders Ranges: The fossils preserved in the ancient sea-floor at Ediacara record the first known multicellular animal life on Earth that predates the Cambrian.
Define relative dating
Ranking strata as older or younger than others but not giving an actual age.
Define stratigraphy and explain how it is based on the use of index fossils.
The branch of geology concerned with comparing and dating the order and relative position of strata and their relationship to the geological timescale using Index fossils within the rocks, as fossils are the same age as the rocks in which they are found.
