CH 25 outline ADA.docx

Chapter 25: The History of Life on Earth Overview

The largest fully terrestrial animal in Antarctica is a 5-mm-long fly.
Five hundred million years ago, Antarctica was surrounded by warm ocean waters filled with tropical invertebrates.
The continent was later covered with forests where dinosaurs and predatory "terror birds" hunted.
Past organisms were significantly different from modern ones.
Macroevolution: Broad patterns of evolution above the species level, including:
- Evolution of terrestrial vertebrates.
- The impact of mass extinctions on life diversity.
- Key adaptations like flight in birds.

Chemical and physical processes on early Earth fostered the emergence of very simple cells through natural selection.
Four Main Stages:
1. Abiotic synthesis of small organic molecules (monomers).
2. Joining of monomers into macromolecules.
3. Packaging into protocells, which are droplets with membranes maintaining distinct internal chemistry.
4. Origin of self-replicating molecules, enabling inheritance.

The scenario is speculative but leads to testable predictions.
Earth formed about 4.6 billion years ago from dust and rocks around the sun.
Life was unlikely in the first few hundred million years due to bombardment:
- Collisions generated heat vaporizing water.
The first atmosphere was likely reducing, thick with water vapor, nitrogen, carbon dioxide, methane, and ammonia.
After cooling, water vapor condensed to form oceans. High ultraviolet radiation contributed to organic compound formation.
Scientists postulated that organic compounds from inorganic precursors formed under early atmospheric conditions (Oparin-Haldane hypothesis).
- Miller-Urey experiment (1953) tested this hypothesis by recreating early Earth conditions, succeeding in producing amino acids and other organic molecules.

Various gas mixtures continue to produce organic molecules.
Meteorites, such as the Murchison meteorite, have revealed amino acids, simple sugars, and nitrogenous bases (uracil).
Laboratory studies indicate spontaneous synthesis of RNA monomers, linking to the origin of life hypothesis.
Protocells with similar properties to life can form spontaneously from simple compounds:
- Formation of vesicles from lipids in water.
- Vesicles can increase in size and carry out metabolic reactions.

RNA likely served as the first genetic material due to its catalytic and self-replicating abilities.
Laboratory experiments demonstrate RNA evolution under abiotic conditions.
Evolution through mutations and natural selection in replicating RNA sequences hints at the emergence of life.

RNA served a dual role in early life before being superseded by DNA as the genetic archive.
DNA is more stable and replicates more accurately than RNA.

Sedimentary rocks are the richest source of fossils, revealing organisms' sequences over time, albeit not their precise ages.
The fossil record illustrates significant biological changes, highlighting extinctions and emerging new groups.
Paleontology aids in predicting fossil locations based on evolutionary relationships and geological dating techniques.

Radiometric dating methods based on radioactive isotopes are essential for determining fossil ages.
Carbon-14 dating applies to recent fossils; older fossils require isotopes with longer half-lives.
Fossils between layers of volcanic rock can yield deeper insights into their ages.

Mammals share distinct anatomical traits, allowing them to form substantial fossil records.
Unique evolutionary features in mammals stem from gradual modifications from their ancestors.

Life's history divided into four eons: Hadean, Archaean, Proterozoic, and Phanerozoic (last half billion years).
The oldest known fossils, stromatolites, date back to 3.5 billion years ago, indicating the early forms of life.
Prokaryotes significantly impacted Earth's environment, leading to the rise of atmospheric oxygen during the oxygen revolution.

The gradual build-up of oxygen in the atmosphere revolutionized life.
Eukaryotic cells evolved through endosymbiosis with prokaryotic ancestors leading to complex structures with specialized functions.

Unicellular eukaryotes led to multicellular forms, culminating in diverse life forms, including plants, fungi, and animals.
The thawing from severe ice ages allowed for significant diversification events in multicellular eukaryotes.

Adaptive radiations often follow major mass extinctions, allowing surviving species to fill newly available ecological niches.
Mass extinctions reshape biological diversity, creating significant impacts that require millions of years for recovery.

Variation in developmental genes can lead to significant morphological changes.
Evolutionary transformations stem from genetic changes influencing organismal development patterns.

Evolution is driven by distinct factors, with no predetermined direction, emerging from natural selection and environmental pressures over time.