Principes of Life, Ch 17 Notes Pt II

17.3 Major Events in the Evolution of Life Can Be Read in the Fossil Record

• Biota: All of the organisms—animals, plants, fungi, and microorganisms—found in a given area.
• Flora: All of the plants found in a given area or time.
• Fauna: All the animals found in a given area or time.

Several factors contribute to the paucity of fossils

• Most organisms live and die in oxygen-rich environments in which they quickly decompose.
• Organisms are not likely to become fossils unless they are transported by wind or water to sites that lack oxygen, where decomposition proceeds slowly or not at all.
• The fossil record is most complete for marine animals that had hard skeletons (which resist decomposition).

Precambrian life was small and aquatic

• Plankton: Aquatic organisms that drift with the current; Photosynthetic members of the plankton are referred to as phytoplankton.
• The “snowball Earth” hypothesis suggests that cold conditions confined life to warm places such as hot springs, deep thermal vents, and perhaps a few equatorial oceans that avoided ice cover.

Life expanded rapidly during the Cambrian

• Cambrian explosion: The name for the rapid diversification of multicellular life that took place during the Cambrian period.

Many groups of organisms that arose during the Cambrian later diversified

• Ordovician: the continents, which were located primarily in the southern hemisphere, still lacked multicellular life. Evolutionary radiation of marine organisms was large for marine life
    * At the end of the Ordovician, as massive glaciers formed over the southern continents, sea levels and ocean temps dropped
    * About 75 percent of all animal species became extinct during the Ordovician
• Silurian: continents began to merge together; Marine life rebounded from the mass extinction at the end of the Ordovician.
    * Animals able to swim in open water and feed above the ocean floor appeared for the first time in the Silurian period
    * Fishes diversified as bony armor gave way to the less rigid scales of modern fishes, and the first jawed fishes and the first fishes with supporting rays in their fins appeared.
    * On land, the first vascular plants evolved late in the Silurian (about 420 mya).
• Devonian: Rates of evolutionary change accelerated; mosses and ferns became more common and grew into large trees that could withstand
    * Seed plants appeared during the Devonian
    * A mass extinction of about 75 percent of all marine species marked the end of the Devonian; cause is uncertain but may have been a meteor
• Carboniferous: Large glaciers formed over high-latitude portions of the southern land masses, but extensive swamp forests grew on the tropical continents.
    * During the carboniferous, Snails, scorpions, centipedes, and insects were abundant and diverse. Insects evolved wings, becoming the first animals to fly.
    * The terrestrial vertebrates split into two lineages; The amphibians became larger and better adapted to terrestrial existence, while the sister lineage led to the amniotes (think snakes)
• Permian: continents merge to form Pangaea; lineages that will form reptiles and mammals separate
    * Permian is a very bad time for environmental conditions

Geographic differentiation increased during the Mesozoic

• Mesozoic: Pangaea begins breaking apart, oceans rise and oxygen increases
• The Mesozoic is divided into three periods: the Triassic, Jurassic, and Cretaceous.
• Triassic: Pangaea remains intact, burrowing animals evolved, conifers and seed ferns were the dominant trees.
    * During the triassic, the first frogs and turtles appeared.
    * A great radiation of reptiles began during Triassic, which eventually gave rise to crocodilians, dinosaurs, and birds.
    * The first mammals appeared in Triassic.
    * The end of the Triassic was marked by a mass extinction that eliminated about 65 percent of the species on Earth.
• Jurassic: Pangaea became fully divided into two large continents; the first lizards appeared; flying reptiles (pterosaurs) evolved; most things were dinosaurs
    * The earliest fossils of flowering plants come from the Jurassic period
    * Laurasia: The northernmost of the two large continents produced by the breakup of Pangaea.
    * Gondwana: The southernmost of the two large continents produced by the breakup of Pangaea; makes up South America, Africa, India, Australia, and Antarctica.
• Cretaceous: Continents as we know them today are broken; sea levels are high; first snakes appeared and everything else diversifies, many groups of mammals appear; flowers diversify
    * At the end of the Cretaceous, almost all animals larger than about 25 kilograms in body weight became extinct; many insects and small mammals
• Cenozoic: Indian subcontinent is still separated from Asia but everything else is moving into place; amphibians, reptiles, and mammals are going through massive radiation; legumes can use nitrogen
    * The Cenozoic is divided into the Paleogene, Neogene, and Quaternary periods
    * Paleogene: hot and humid; increased plankton; grasslands spread and nonwoody plants evolve
    * Neogene: North and South America are connected; Atlantic and Pacific oceans are isolated
    * Quanternary: us today, separated into Pleistocene and the Holocene
      * Pleistocene: drastic cooling and climate fluctuations; many ice ages; animal and plant populations shifted toward the equator; primates divergence that leads to Homo sapiens
      * Holocene: Recent times