Fossils and Dating Flashcards
Paleontology
The study of ancient life
fossils
the remains o once-living organisms that are preserved in the geologic record
Subdisciplines of paleontology
vertebrate paleontology
invertebrate paleontology
paleobotany
Types of fossils
Body fossils and trace fossils
Body fossils
Fossilized remains of actual organisms
trace fossils
Fossilized remains of traces left by organisms (such as bite marks, footprints, burrows, poop [coprolites] etc.)
Fossilization types
Impressions
Ambers
Petrification
Impressions
Fossils where the body of an organism has been pressed into the sediment, leaving an impression that preserves its original shape.
Amber
Hardened and fossilized tree sap, which can preserve organisms [like ants etc.]
Petrification
Fossilization when mineral-rich waters deposit microcrystalline silica in the open spaces between the tissues of an organism
Some important invertebrate fossils
trilobites
brachiopods
ammonoids (or ammonites)
Trilobites
an exticnt group of arthropods found only in the Paleozoic
Brachiopods
somewhat resemble clams, but their shells are perfectly symmetrical, and they are usually very thin
ammonoids
an extinct-group of squid-like animals from the Mesozoic that usually had coiled shells
Correlation
The process of linking or matching rock units over distances in which they are not seen.
Methods of correlation
Index fossils (using biostratigraphy)
radioactive dating methods
magnetic signatures (magnetostratigraphy)
Types of correlation
Physical correlation and temporal correlation
Physical correlation
Rocks are matched according to shared composition and structures
Temporal correlation
rocks are matched according to the time of their formation
Principle of faunal succession
where organisms follow one another in a definite and recognizable order within sedimentary rocks
Index fossils
Key fossils used in correlating strata
Good index fossils are very common and very restricted in their stratigraphic horizons.
geologic column
A large-scale pattern to fossils seen in the strata around the world
Radiometric dating
aka radioisotope dating
The most common method used to get absolute (exact) ages for rocks. It depends on the radioactive decay of isotopes. Some isotopes are unstable and will convert to different isotopes through radioactive decay.
4 major types of radioactive decay
Alpha decay
Beta decay
Nuclear fission
Electron capture
Alpha decay
The nucleus emits a cluster of two protons and two neutrons called an alpha particle (a helium nucleus). The daughter isotope is of a different element than the parent isotope.
Beta decay
A neutron in the nucleus emits a negative beta particle, which is identical to an electron in size and charge. The neutron, after losing the beta particle, becomes a proton. This increases the atomic number by 1 (changes elements), but the mass stays the same.
nuclear fission
The parent isotope splits into two smaller daughter isotopes, often with the release of additional nuclear materials and energy. As these daughter products shoot away from each other, they leave microscopic lines (called fission tracks) in minerals.
Electron capture
An electron from outside the atom collides with a proton in the nucleus. The collision fuses the electron and the proton, canceling their charges and producing a neutron. It’s essentially a reversal of beta decay.
