Key Points in this Chapter

KEY POINTS IN THIS CHAPTER

• Geologic time was long, divided into eons, eras, periods, epochs, and more.

• Most eras were marked by a large change in the earth's climate and major species on earth.

• The first common fossils were of things like mollusks, brachiopods, and arthropods but very early fossils found on earth were of algae.

• The transition from anaerobic to aerobic organisms happened when oxygen was produced in large numbers by photosynthetic organisms.

• The Permian-Triassic extinction happened when the oceans acidified with dissolved carbon dioxide emitted by large volcanoes in Siberia.

• Carbon dating is not used much in rock dating but there are many other dating features used for this process. Most are based on uranium decay or Potassium decay over time or the effects of radioactive decay in crystals.

• Stratigraphy involves several principles that help to relatively date fossils and other aspects of rock.

• There are different kinds of fossils in rock that will say something about living things from along ago.