Earth Science: Review Part 2

Relative Age Dating and Absolute Age Dating

• Relative age dating: determines the sequence of geological events and the relative ages of rock layers without providing specific numerical ages
• Absolute age dating: determines the exact age of a rock, fossil, or geological event in years, usually through the use of radiometric dating techniques
• Comparison: relative age dating determines the order of events, while absolute age dating provides specific numerical ages
• Precision: relative age dating is less precise and does not offer exact dates, whereas absolute age dating provides exact ages in years
• Techniques: relative age dating relies on principles of stratigraphy and fossil correlation, whereas absolute age dating uses radiometric and other quantitative techniques

Types of Fossils

• Body Fossils: consist of the actual physical remains of an organism, such as bones, teeth, shells, and leaves
  • Formation: rapid burial of hard parts, preventing decomposition
  • Examples: dinosaur bones, mammoth tusks, and trilobite exoskeletons
  • Characteristics: provide direct evidence of an organism's structure and appearance
• Trace Fossils (Ichnofossils): record the activities of organisms, such as footprints, burrows, and coprolites (fossilized dung)
  • Formation: interaction with a substrate, leaving behind an impression or disturbance
  • Examples: dinosaur footprints, worm burrows, and trilobite tracks
  • Characteristics: provide indirect evidence of an organism's behavior, movement, and interactions with its environment
• Mold Fossils: an impression left in the substrate where an organism was buried
  • Formation: decay or dissolution of an organism, leaving an empty space
  • Examples: impressions of shells or leaves in rock
  • Characteristics: capture the external shape and surface details of the organism
• Cast Fossils: created when a mold is filled with sediment or mineral deposits
  • Formation: minerals or sediments fill the empty space and solidify
  • Examples: casts of shells or bones
  • Characteristics: provide a three-dimensional representation of the organism's external features
• Permineralized Fossils: form when minerals precipitate into the pores of an organism's remains
  • Formation: groundwater rich in minerals flows through the remains
  • Examples: petrified wood and bone fossils
  • Characteristics: retain detailed internal and external structures of the original organism
• Amber Fossils: organisms or parts of organisms preserved in tree resin
  • Formation: organisms trapped in sticky tree resin, which eventually hardens and fossilizes
  • Examples: insects, spiders, and plant material encased in amber
  • Characteristics: preserve organisms in remarkable detail, including soft tissues and coloration
• Carbonized Fossils: form when organic material is compressed and leaves a carbon imprint on rock
  • Formation: organisms buried under fine sediment, subjected to pressure
  • Examples: fern leaves and fish skeletons in shale
  • Characteristics: typically flat and display fine details of the organism's structure

Fossil Formation Processes

• Permineralization: mineral-rich water permeates the pores and cavities of an organism's hard parts
  • Environment: rapid burial, mineral-rich water
  • Characteristics: highly detailed fossils, retain both external and internal structures
• Carbonization: organism buried under fine sediment, subjected to pressure, driving off volatile elements
  • Environment: anoxic environments, rapid sedimentation
  • Characteristics: detailed, flat fossils, preserve fine details of morphology
• Molds and Casts: organism buried in sediment, decays or dissolves, leaving an empty space
  • Environment: soft, fine-grained sediments, rapid burial
  • Characteristics: provide external shapes and surface details, do not contain original organic material
• Amber Entrapment: small organisms trapped in sticky tree resin, which hardens and fossilizes
  • Environment: forested areas, resin-producing trees
  • Characteristics: preserve entire organisms, including soft tissues, with remarkable detail

Index Fossils

• Definition: fossil of an organism that lived during a relatively short, well-defined geological time period and was widespread geographically
• Importance: crucial tools in geology and paleontology for dating and correlating the age of rock layers
• Characteristics: short geological range, widespread geographic distribution, easily recognizable

Half-Life and Radioactive Decay

• Definition: half-life is the time required for half of the atoms in a sample of a radioactive substance to decay into a stable form
• Importance: fundamental in understanding radioactive decay, widely used in geology, archaeology, and nuclear medicine
• Application: used to date objects, determine the age of rocks and fossils

Alpha and Beta Decay

• Alpha Decay: emits an alpha particle (2 protons and 2 neutrons), decreases atomic number by 2, and mass number by 4
• Beta Decay: emits either an electron (beta-minus) or a positron (beta-plus), changes atomic number, no change in mass number
• Comparison: differ in particles emitted, changes in atomic number and mass, and penetration abilities

Mineral Properties

• Streak: color of a mineral in its powdered form
  • Testing Method: use a streak plate, drag the mineral across the plate to produce a line of powder
  • Example: hematite leaves a reddish-brown streak, while pyrite leaves a greenish-black streak
• Hardness: measures a mineral's resistance to scratching
  • Testing Method: perform scratch tests using reference materials of known hardness
  • Example: quartz has a hardness of 7, can scratch glass
• Cleavage: describes how a mineral breaks along specific planes of weakness
  • Testing Method: examine the mineral for natural planes of separation, gently tap the mineral with a hammer or use a knife to see if it breaks along flat surfaces
  • Example: mica exhibits perfect cleavage in one direction, allowing it to split into thin sheets
• Luster: way a mineral reflects light from its surface
  • Testing Method: observe the mineral under a good light source, describe how the light interacts with the surface
  • Example: galena has a metallic luster, while quartz typically has a vitreous luster