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Chapter 25 The History Of Life On Earth Study Guide

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Recommended: Chapter 17 biology the fossil record

Chapter 25: The History of Life on Earth
Concept 25.2 – The fossil record documents the history of life
• The fossil record is what gives us access to a view of what the world was like long ago o We have a sight of how life has evolved over the course of billions of years

A. The Fossil Record
• Fossils are primarily found in sedimentary rock
• Strata are sedimentary rock layers in which fossils have amassed o The fossil record is based on the sequence of this
• There are also other types of fossils o Amber and ice
• The fossil record is evidence of the changes, as well as the differences between, Earth’s organisms throughout time
• The fossil record is extremely important, however it doesn’t completely explain evolutionary change
• The fossil …show more content…

• Absolute dating refers to an age given in years, not relative terms
• Radiometric dating is a common technique used to determine the absolute age of a fossil based on the decay of radioactive isotopes o “parent” isotope –> decays –> “daughter” isotope
• Half-life expresses the rate of decay, the time required for 50% of the parent isotope to decay o Each radioactive isotope has its own unique half-life
• Isotopes of elements collect within organisms throughout the duration of their lives, and fossils contain these isotopes
• For fossils up to 75,000 years old, it is possible to determine their age by measuring the ratio of carbon-14 to carbon-12 within those fossils o (ELABORATION: When a living organism with carbon-12 and carbon-14 dies, carbon is no longer accumulated –> the amount of carbon-12 within its tissues remains the same over time –> carbon-14 decays into nitrogen-14)
• For older fossils, it is more difficult to determine their ages because they contain too little carbon-14; however, other radioactive isotopes with longer-half lives can be used, instead
• The ages of older fossils in sedimentary rock can be indirectly measured by referring the half-life of the radioactive isotopes trapped in the surrounding

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