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GEOLOGIC TIME SCALE 1. What is the basis of the Geologic Time Scale? The Geologic Time Scale is based on fossil evidence in Earth’s rocks and the age of the rocks.

2. Describe the divisions of the geologic time scale. It is divided into four divisions and subdivisions. (Era and Period.)

3. During what era and at approximately what date does fossil evidence suggest life had evolved on Earth? What form of life was this? Fossil evidences suggest that a bacterium evolved 3.5 billion years ago in the Precambrian era.

4. What forms of living things characterized the Cambrian period? Marine invertebrates such as marine worms, primitive arthropods, and echinoderms.

5. During what era did the first vertebrates evolve? What were these vertebrates? The rise of the first vertebrates is synonymous with the Paleozoic Era, a span of increasing ecological complexity where the first explosion of life occurred in the seas. In this fully illustrated volume, "The First Vertebrates" examines the dramatic rise of vertebrate life in the Paleozoic seas with the development of early fish, including jawless fish, fish with teeth and jaws, early sharks and other cartilaginous fish, and bony fish, the ancestors of present-day fish species.

6. The dinosaurs and many other species became extinct in a relatively short period of time that marks what is called the K-T boundary, which stands between the Cretaceous and Tertiary periods. About how long ago did the dinosaurs become extinct? About 65 million years ago

7. Imagine you found a fossil of a bird that dates to 213 million years. Why would this find be astonishing to scientists? Based on fossils, birds did not evolve until 145 million years ago. So, Scientist might be curious on how you found a fossil of a bird, which dates back 213 million years ago.

8. Suppose a geologist finds a layer of rock that can be dated to 320 million years ago. Layers from which periods would be expected to be above and below the newly discovered layer? The Permian layers would be above the 320-million-year-old Carboniferous, and the Devonian layers would be blow.