Unit 12: Geologic History

NYS Earth Science Curriculum (nysed.gov)

1.2i The pattern of evolution of life-forms on Earth is at least partially preserved in the rock record.

• • • Fossil evidence indicates that a wide variety of life-forms has existed in the past and that most of these forms have become extinct.

    • Human existence has been very brief compared to the expanse of geologic time.

1.2j Geologic history can be reconstructed by observing sequences of rock types and fossils to correlate bedrock at various locations.

• • • The characteristics of rocks indicate the processes by which they formed and the environments in which these processes took place.

    • Fossils preserved in rocks provide information about past environmental conditions.

    • Geologists have divided Earth history into time units based upon the fossil record.

    • Age relationships among bodies of rocks can be determined using principles of original horizontality, superposition, inclusions, cross-cutting relationships, contact metamorphism, and unconformities. The presence of volcanic ash layers, index fossils, and meteoritic debris can provide additional information.

    • The regular rate of nuclear decay (half-life time period) of radioactive isotopes allows geologists to determine the absolute age of materials found in some rocks.