Fossilization Processes and Geological Dating Principles

Fossilization Processes and Paleontological Insights

Other fossilization processes include: 1) preservation in amber, 2) conservation in asphalt, and 3) preservation in ice.

Fossils provide us with essential data:

• Life in the past: Fossils are the only documents we have about the organisms that populated the Earth in other epochs. We can know the anatomy of the body.
• The environment: The atmosphere in the rock was formed by what it contains; each organism occupies a given habitat, which can be marine or continental.
• The age of the rock: The rock was formed when it contains specific fossils. Just as living beings have lived on Earth and changed through time periods, by knowing when a particular organism lived, we know the age of the rock that fossilized it.

Geological Dating Methods

Varves in Glacial Lakes

Covered lakes are formed with a layer of ice in winter that melts in summer. Each year, two layers of sediment are deposited: a clear layer and a dark layer. The clear sediment corresponds to the summer and consists of coarser materials. The very fine materials remain in suspension and are deposited in winter when the ice surface leaves the waters calm. Its dark color is due to the presence of unoxidized organic matter.

Coral Growth Rings

Some ancient bell-shaped corals originated a thin daily plate of calcium carbonate. A small constriction marks the separation between one year and another, so the number of plates for each year can be counted. The lunar attraction is holding back the Earth's rotation at a rate of 20 seconds every million years.

Fundamental Principles of Dating

Principle of Original Horizontality

Strata are deposited as sediments forming horizontal layers. If a set of layers is found that are not arranged horizontally, it means that after their formation, they have undergone some type of stress that changed their original disposition.

Principle of Lateral Continuity

Originally, layers extend laterally and taper at their edges. The age is the same throughout the entire surface of a single layer.

Principle of Superposition

Sediments are deposited over each other, so in a series in its original arrangement, the stratum located below is the oldest and the one above is the most modern.

Roof and Wall Criteria

Desiccation Cracks

Drying clay sediments are formed. They are open at the surface and closed in depth.

Ripple Marks

Waves formed by wind or water. They present the sharpest peaks toward the ceiling (top) and the most rounded toward the wall (bottom). Most frequent ripple marks originate in the sediment.

Cross-Bedding

This may originate from deposits of sand that have been transported by the wind.

Graded Bedding

The deposit is formed by materials of different sizes that were transported by a water stream.