P337\Section 4 Geologic Time Scale

1a How long ago did the Earth form? 4.6 billion years ago

Summarize the process by which scientists determined the age of Earth. Scientists studies rock layers and fossils worldwide and placed Earth’s rock layers in order by relative age. Later, radioactive dating helped them determine the absolute ages of the divisions.

What are the basic units into which the geologic time scale is divided? The geologic time scale is divided into eras and periods.

Study figure 14. (p336) Which major division of time was the longest? Precambrian When did it begin? 4.6 BYA When did it end? 544 MYA

Place the following in the correct order from earliest to latest: Tertiary, Jurassic, Quaternary, Triassic, and Cretaceous. Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary

Section 5 Early Earth p. 341e 1a How long ago did the Earth form? The Earth formed about 4.6 billion years ago

Summarize the process by which scientists determined the age of the Earth. Scientists used radioactive dating of rocks from Earth and moon to determine the age of the Earth.

What physical features formed during Earth’s first several hundred million years? Oceans, the atmosphere, and continents were formed.

How did volcanic eruptions and comets change early Earth? Volcanic eruptions released carbon dioxide into the atmosphere, and comets released water vapor.

What caused water erosion to begin on Earth’s surface? Rain

What do scientists think were the first organisms to evolve on Earth? Organisms similar to our present day bacteria were probably the first life forms.

How would Earth’s atmosphere be different if organisms capable of photosynthesis had not evolved? The Earth’s atmosphere would have little or no oxygen. A by-product of photosynthesis is oxygen.