Evidence of Evolution: Chapter 13 Study Notes

Evidence of Evolution

Introduction

Evolution is the process by which species change over time, and its evidence is found throughout Earth's history. Scientists use multiple lines of evidence, including fossils, anatomical features, and molecular data, to understand how life has evolved and diversified.

Geologic Timescale and Evolution

Geologic Timescale

The geologic timescale divides Earth's history into eons and eras based on biological and geographical events. It helps scientists contextualize evolutionary changes over billions of years.

• Origin of Life: Life on Earth arose approximately 3.8 billion years ago.

• Geologic Timescale: Used to organize major events in Earth's history, such as the appearance of life and mass extinctions.

• Environmental Changes: Changes in the environment select for changes in body structures and molecules, driving evolution.

Fossil Evidence

Paleontology and Fossils

Paleontology is the study of fossil remains or other clues to past life. Fossils are the preserved remains or traces of ancient organisms and provide direct evidence for evolution.

• Fossil Record: Fossils document the history of life on Earth and allow researchers to test evolutionary predictions.

• Common Ancestry: Comparing fossils and living organisms suggests that all life derived from a common ancestor.

Formation of Fossils

Fossils can form in several ways, each preserving different aspects of ancient life.

• Compression: Organisms are compressed in sediment, leaving a thin, carbon-rich film.

• Petrification: Organic matter is replaced by minerals, turning remains to stone.

• Impressions: Organisms leave imprints in sediment, which hardens into rock.

• Casting: Decayed organisms leave a cavity that is later filled with minerals, forming a cast.

• Intact Preservation: Organisms are preserved whole, often in amber or by rapid burial in oxygen-poor environments.

Limitations of the Fossil Record

• Incomplete Record: Not all organisms fossilize, especially those with soft bodies.

• Destruction: Erosion and plate tectonics can destroy fossils.

Dating Fossils

Determining the age of fossils is crucial for reconstructing evolutionary timelines.

• Relative Dating: Uses the position of fossils in rock layers to estimate age. Lower layers are older than upper layers.

• Absolute Dating: Uses chemical methods, such as radiometric dating, to measure the decay of isotopes (e.g., 14C) and calculate the age of fossils.

Radiometric Dating and Carbon Isotopes

• Living organisms accumulate 14C and 12C. After death, 14C decays with a half-life of 5,730 years.

• By measuring the ratio of 14C to 12C, scientists estimate how long ago an organism died.

Equation:

$N = N_0 imes (1/2)^{t/T_{1/2}}$ Where $N$ is the remaining isotope, $N_0$ is the original amount, $t$ is time, and $T_{1/2}$ is the half-life.

Biogeography

Species' Geographical Locations

Biogeography studies the distribution of species across the planet and provides evidence for evolution.

• Plate Tectonics: Earth's continents have moved over time, affecting species distribution.

• Pangaea: Fossil evidence shows that continents were once joined in a supercontinent, influencing evolutionary events.

• Wallace's Line: Distinct species distributions on either side of this line in Asia and Australia reflect independent evolution.

Anatomical Evidence

Common Descent and Homology

Comparing anatomical features helps determine evolutionary relationships.

• Homologous Structures: Structures inherited from a common ancestor, such as similar bones in vertebrate forelimbs.

• Vestigial Structures: Remnants of structures that had functions in ancestors but are no longer functional (e.g., whale pelvis, blind mole eyes).

• Analogous Structures: Structures that evolved independently for similar functions (e.g., wings in birds and insects), a result of convergent evolution.

Comparison Table: Homologous vs. Analogous vs. Vestigial Structures

Type	Definition	Example
Homologous	Inherited from a common ancestor	Vertebrate forelimbs
Analogous	Similar function, different origin	Bird and insect wings
Vestigial	Lost original function	Whale pelvis

Key Concepts and Review Questions

• Geologic Timescale: What is it and why is it important?

• Fossil Dating: Distinguish between relative and absolute dating.

• Biogeography: How does it provide evidence for evolution?

• Anatomical Evidence: What can homologies reveal about evolution?

Example Application: The streamlined shapes of dolphins and sharks are analogous, resulting from convergent evolution.

Additional info: These notes expand on textbook slides and fill in academic context for clarity and completeness.