Chapter 8 Fossils

Fossils

The remains of once-living organisms that have been transformed into rock through a slow process of chemical replacement

• Direct physical evidence of past life and evolution

Paleontology

The study of fossils in order to learn about the past

• Finding + analyzing fossils and study of extinct organisms, environments, and evol. process

Taphonomy

The study of what happens to an organism’s remain after death

• Includes process of fossilization

Limitations of Fossil Record

1. Majority of organism remaines do not fossilize, only is possible in rare circumstances

2. Environmental condition impact likeliness of fossilization

3. Fossil record: Limited to only specimens that fossilized and found (limited to only certain time periods)

Geological Perspective

Earth is 4.6 billion yrs old

• Cenozoic Era: Rise of Mammals = emergence of primates, evolution of primates, emergence of hominins → humans

Relative Dating

Provides chronological, relative age, and “after x and before y”

Relative Dating Methods: Stratigraphy and the Law of Superposition

• Steno’s Law of Superposition: Bottom layers of strata are older, top, layers are younger

• Stratigraphy: Basic methof of relative dating, determine their age in relation to each other

Relative Dating Methods: Stratigraphic Correlation

Process of matching up strata from across regions through the analysis of specific chemical properties of the strata

• Allows for comparison of multiple sites across dffierent regions and higher degree of precision

Absolute Dating Methods

Provides a specific point in time = numerical age

Absolute Dating Methods: Radiometric Dating

Analysis of radioisotopes

• Isotopes: Variants of the same element based on number of neutron in the atom

  • Same number of protons but different number of neutrons

  • Stable = non-radioactive

  • Unstable = radioactive → transform over time (Protons change the element)

• “Half-life”: The rate of this change

  • Measurable rate of radioactive decay

  • EVERY radioisotope has a specific half-life

Absolute Dating Method: Radiocarbon Dating

All living things remains contain carbon

• Isotopes: Carbon-12 is stable, Carbon-12 is unstable

  • Carbon-14 decays, some neutrons turns into protons → turn into nitrogen

• C-14 decays, C-12 does not decay when an oragnism dies

  • Half-life = every 5,370 yrs exactly half of the remainings C-14 becomes nitrogen

• Only works for those for fossils that exist in the past 50,000 yrs

Absolute Dating Methods: Dating Volanic Rock

Radiopotassium dating: “Clock in rock”

• Dates older than 200,000 yrs

• Important in East Africa: Best ways to date hominin fossils older than 200,000 yrs