GEOLOGIC TIME SCALE

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Across
  1. 2. In the latter half of this epoch, increased mountain building, combined with changing ocean currents and polar ice on Antarctica, led to decreased rainfall, increased seasonality, and cooler temperatures. There were great mammal migrations from continent to continent over the land bridges. For example, elephants first migrated to North America at this time.
  2. 6. Subdivision of Era.
  3. 11. It is the period in which birds diversified and expanded in numbers, and they may have been the reason that flying reptiles decreased significantly. There were many new mammals, including the three groups that live today. Due to the appearance of flowering plants, many modern groups of insects appeared and began to diversify, including ants, termites, bees, butterflies, aphids, and grasshoppers.
  4. 12. It is the period when Pangaea now existed as a super continent that contained almost all the land area of the world. As many swamps dried up, amphibian populations dwindled. Reptiles diversified and spread across the land.
  5. 13. Largest formal division of geologic time.
  6. 15. Subdivision of Eon.
  7. 16. The earliest span of Earth's history, lasting from the planet's formation about 4.6 billion years ago to the start of the Cambrian Period 541 million years ago.
  8. 17. It is the period when much of Earth’s carbon-rich coals formed because many places on Earth were swampy. On land, the first reptiles appeared, and they laid the first shelled eggs.
  9. 18. It is the period in which there is no continents near the poles, very little glacial ice. The Earth had no polar ice caps. Marine life flourished and most major groups of invertebrates first appeared.
  10. 20. In this epoch, the position of the continents was essentially the same as it is today. There was a significant number of large animals (i.e., mammoths, mastodons, saber-toothed cats, and giant ground sloths), but few of them survived. By the end of the epoch, modern humans had spread throughout most of the world except Antarctica.
  11. 21. It is the period in which the part of Gondwana that is northern Africa today moved over the South Pole, triggering an ice age. Algae and sponges dominated reefs and jawless, armored fish were common.
  12. 23. It is the period in which so much of the land was near the equator, the climate was warm and mild; it was a greenhouse age. The shallow, tropical seas had abundant reefs and were home to a myriad of sea life and sharks became common at this time.
  13. 24. It is the era known as the "Age of Reptiles.” This era was dominated by dinosaurs, the breakup of the supercontinent Pangaea, and the rise of early mammals and birds.
  14. 25. It is the period in which rift basins (or rift valleys) developed between North America and Europe and between Africa and South America. The first dinosaurs, marine reptiles, lizards, and tortoises appeared.
Down
  1. 1. It is the period in which warm tropical greenhouse conditions occurred worldwide. Giant plant-eating dinosaurs roamed the Earth with smaller but vicious carnivores stalking them. Cycads (evergreen, cone-bearing, palm-like plants) became so abundant and diverse that this period is sometimes called the "Age of Cycads."
  2. 3. During this epoch, temperatures were warmer than during any other time in the Cenozoic. There was a lot of rainfall but no seasons, no glaciers, and similar temperatures throughout most of the globe. Palm trees and alligators were able to live within the Arctic Circle.
  3. 4. It is the period in which Gondwana moved away from the South Pole, many of the glaciers melted, and the ice age ended. The climate was similar to today’s, with cold weather and glaciers near the South Pole and warmer weather near the equator. The first fish with jaws appeared. The first evidence for animals on land occurred in the Silurian: scorpions and millipede-like animals.
  4. 5. This Era is known as the "Age of Ancient Life." It began with the Cambrian explosion of diverse marine organisms and ended with a massive extinction event.
  5. 7. The climate, which had been warm and moist in the Eocene, became cool, dry, and seasonal in this epoch. As temperatures lowered, seasonality increased, grasslands appeared, and the body size of mammals increased. A huge, hornless rhinoceros from Asia was the largest land mammal ever to live.
  6. 8. The final eon of the supereon, notable for the oxygen buildup in the atmosphere and the appearance of the first multicellular organisms.
  7. 9. The earliest time when Earth formed, melted under intense heat, and slowly cooled to form a solid crust and early oceans. Its name is from the Greek god of the underworld
  8. 10. It is an epoch in which climate was much warmer and more uniform than today. After the massive extinction at the end of the Cretaceous, evolution once again proceeded rapidly. With their dinosaur competitors gone, many new mammals evolved. The first rodents, armadillos, primitive primates, and ancestors to modern mammalian carnivores appeared.
  9. 14. Subdivision of Period.
  10. 16. By the beginning of this epoch, the continents were in very similar positions to where we find them today. Armadillos, ground sloths, opossums, and porcupines moved into North America, and dogs, cats, bears, and horses moved into South America. Many animals became extinct because of the new competition.
  11. 19. The time when single-celled microbial life first appeared and tectonic plates began building the first continents.
  12. 22. This era is originally spelled Kainozoic, was introduced by English geologist John Phillips in an 1840. It is the most recent of the three major subdivisions of animal history.