HISTORY OF EARTH

• What principle is the basis of uniformitarianism?


  The present is the key to the past.
• How do different types of rocks provide hints about Earth's past?

  They record volcanic activities, plate movements, and climate conditions.
• What are the three main types of rocks and their significance?

  • Igneous: records volcanic activities and specific ages.
  • Metamorphic: indicates plate movements and continental drift.
  • Sedimentary: holds climate records, previous environmental conditions, and fossils.
• What is the primary composition of rocks exposed at the Earth's surface?

  Most are sedimentary, formed from particles of older rocks.
• What does gravel become when it solidifies?

  Conglomerate.
• What does sand become when it solidifies?


  Sandstone.
• What does mud become when it solidifies?

  Mudstone or shale.
• What are the two main methods to determine the age of stratified rocks?

  • Relative Dating: determines the sequence of events without specific ages.
  • Absolute Dating: provides actual dates or date ranges in years.
• What is relative dating?


  It determines if one rock or event is older or younger than another.
• What are rock layers called?

  Strata.
• What is stratigraphy?


  The science of strata and their characteristics over time.
• Who studied the relative positions of sedimentary rocks?

  Nicholas Steno.
• What does Steno's Law of Original Horizontality state?


  Most sediments were originally laid down horizontally.
• What does the Law of Superposition state?


  A given bed of sedimentary rock must be older than any bed above it.
• What does the Principle of Crosscutting Relations indicate?


  Any rock or fault that cuts across others is younger than those it cuts.
• What does the Law of Lateral Continuity suggest?


  All rock layers are laterally continuous and may be disrupted by later events.
• What does the Principle of Inclusion state?


  Any inclusion found in rock layers is older than the rock that contains it.
• What is an unconformity?


  A surface that reflects a time of nondeposition or erosion.
• What does the Law of Faunal Succession state?


  Fossils occur in a definite sequence and predictable manner across locations.
• Why are fossils important for relative dating?


  They help determine the relative ages of sedimentary rocks.
• What is biostratigraphy?


  • Study of the order in which fossils appeared and disappeared through time.
  • Helps in understanding the relative ages of rocks.
• What is correlation in geology?


  • A matching process where fossils help match rocks of the same age.
  • Useful even when rocks are found far apart.
• What are index fossils?


  Fossils characteristic of a particular span of geologic time or environment.
• What is the most abundant index fossil?


  Trilobites.
• How did the discovery of radioactivity change the understanding of Earth's age?


  It allowed for the assignment of ages in thousands, millions, and billions of years.
• What is absolute dating?


  • Methods that provide an actual date or date range in years.
  • Different from relative dating, which only orders events.
• How do scientists determine the absolute ages of rocks and fossils?


  By analyzing isotopes of radioactive elements.
• What are isotopes?


  Atoms with the same number of protons but different numbers of neutrons.
• What are radioisotopes?


  Radioactive isotopes that contain an unstable combination of neutrons and protons.
• How can the relative amounts of stable and unstable isotopes determine age?


  By analyzing the decay of unstable isotopes into stable ones.
• What is half-life?


  The time needed for half of a radioactive substance to undergo decay.
• What are the half-lives of common isotopes?


  • Uranium-235: 704 million years
  • Potassium-40: 1.25 billion years
  • Uranium-238: 4.5 billion years
  • Thorium-232: 14.0 billion years
  • Rubidium-87: 48.8 billion years
• How much Np-240 remains after 4 hours if the half-life is 1 hour and the original amount is 60 grams?


  1. 5 grams.
• How much Cf-251 remains after 800 years if the original amount is 100 grams?


  1. 25 grams after 4 half-lives.
• How much Ac-225 remains after 720 hours if the half-life is 10 days and the original amount is 8.0 µg?


  0.5 µg remains after 36 half-lives.
• How much Rubidium-87 remains after 36,000 minutes if the half-life is 5 days and the original amount is 235 grams?


  1. 375 grams remains after 10 half-lives.
• How long will it take for 18.0 grams of Ra-226 to decay to 2.25 grams if the half-life is 1600 years?


  4800 years.
• What is radiometric dating?


  • A method to determine the absolute age of a sample.
  • Based on the ratio of parent material to daughter material.
• What is the Potassium-Argon Method?


  • Uses potassium-40 with a half-life of 1.3 billion years.
  • Mainly used to date rocks older than 100,000 years.
• What is the Uranium-Lead Method?


  • Uses U-238 with a half-life of 4.5 billion years.
  • Mainly used to date rocks older than 10 million years.