Relative dating block diagrams
Many of these organisms have left their remains as fossils in sedimentary rocks.
Geologists have studied the order in which fossils appeared and disappeared through time and rocks. Fossils can help to match rocks of the same age, even when you find those rocks a long way apart.
For a fossil to be a good index fossil, it needs to have lived during one specific time period, be easy to identify and have been abundant and found in many places. If you find ammonites in a rock in the South Island and also in a rock in the North Island, you can say that both rocks are Mesozoic.
Different species of ammonites lived at different times within the Mesozoic, so identifying a fossil species can help narrow down when a rock was formed.
These strata make up much of the famous prominent rock formations in widely spaced protected areas such as Capitol Reef National Park and Canyonlands National Park.
From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone.
The method of reading the order is called stratigraphy (layers of rock are called strata).
(3) A volcanic eruption destroyed rock layer 3 in outcrop B. Deposition – new sediments deposited on top of the buried eroded surface 1. 2 criteria of good index fossils: • • Life form lived over a wide geographic area – horizontal distribution Life form existed for a short period of time – short vertical distribution Location A Location B Location C Rock layer 1 W W W Rock layer 2 W Rock layer 3 W Z X Z Y X Z X Z Which letter would make a good index fossil?Superpositionyoungest to oldest GRAND CANYON- LAW OF SUPERPOSITION YOUNGEST ON TOP OLDEST ON BOTTOM • In the 17th C., Nicolas Steno made an important observation: "Sediments are usually deposited in horizontal layers." He called this “ORIGINAL HORIZONTALITY” The Principle of...• ORIGINAL HORIZONTALITY: Folds and tilts are younger than rocks themselves Folds/Tilts FOLDS - TILTS The Principle of...“Time Line” (ex) – older or younger • ABSOLUTE DATING: actual date determined by radioactive decay “Clocks in Rocks” (ex) – 50 million years ago The Principle of...• SUPERPOSITION: in a sedimentary sequence the OLDEST will be on BOTTOM and YOUNGER will always be on TOP (if undisturbed – flat and level).