Fossils & The History Of Life Flashcards
How biologists define “life”:
-cellular organization
-must be able to respond to external stimuli and assimilate energy not grow, develop, and reproduce by regulating and coordinating internal processes
-homeostasis
-contains a complex genetic code allowing for adaptation and evolution
The ability not maintain a constant state of internal conditions that differs from the outside environment.
Homeostasis
The preserved remains of an organism.
The impression, trace, or track of an organism.
Fossil
Modes of Fossil Formation (6 ways)
-permineralization
-replacement
-compression
-encasement
-impressions
-trace fossils
Mode of fossil formation.
Dissolved minerals in groundwater permeate soft tissues, then crystallize to form rock that is shaped like the organism.
-hard tissues like bones, teeth, or wood are left behind
-most common method of fossil formation
Permineralization
Mode of fossil formation.
Similar to permineralization, except hard tissues are dissolved and replaced by minerals.
Replacement
Mode of fossil formation.
Heat and pressure cause the release of hydrogen and oxygen from the remains of an organism, leaving behind only a thin layer of carbon residue.
-most commonly occurs through carbonization
-occurs more often with plants than animals
Compression
Mode of fossil formation.
The entire body of an organism can be preserved if frozen, dried, or trapped in tar or resin that hardens into amber.
-soft tissues still degrade and decompose
Encasement
Mode of fossil formation.
Casts and molds.
The rigid outer surface of an organism can form an imprint in sediment as it decomposes.
Impressions
Mode of fossil formation.
An organism moving over soft sediment leaves tracks or trails.
-these markings are preserved if the sediment hardens or is covered by another layer
Trace Fossils
The organic molecules left behind by an organism.
-most can be found in kerogen
Molecular Fossils
Solid, water-insoluble organic matter embedded in rock (along with coal and shale).
Kerogen
Traces of organic chemicals that indicate former life.
Chemical Fossils
Estimates the age of a feature based on the layers around it.
Relative Dating
Used quantitative, laboratory-based techniques to determine the age of an object or feature.
-typically focuses on radioactive elements or changes in the Earth’s magnetic field
Absolute Dating
Only compares the age of things (ex. before X but after Y).
With fossils, done by comparing layers in which fossils are found n(older layers are always underneath newer ones).
Relative Dating
Come from organisms that were known to live in a specific time period and in many places.
Index Fossils
Done through radioactive dating.
Absolute Dating
Radioactive isotopes of some elements exist in nature and they decay at a steady rate.
-each isotope has a known half life and by comparing the amount that has decayed to the amount that would have been there originally, the absolute age can be determined
Radioactive Dating
Relative dating methods:
The Law of Superposition
Cross-Cutting Relationships
Relative Dating Method.
States that lower strata are older than the layers deposited on top of them, and the oldest rocks are at the bottom.
The Law of Superposition
Relative Dating Method.
A geological principle stating that the geological feature that intrudes into another is younger than the feature it intrudes into.
-these features are usually created by fault movements and span multiple strata
Cross-Cutting Relationships