History of Life Paleozoic

Phanerozoic Eon

• Timeframe: ~541 million years ago (mya) to present

• Divisions: 3 major eras: Paleozoic, Mesozoic, and Cenozoic

• Major Events:

  • Rapid emergence of all major animal, fungi, and plant lineages

  • Invasion of land by life forms

  • Diversification of modern lineages

  • Significant extinction events (5 major) leading to adaptive radiations

Paleozoic Era

• Timeframe: 541-252 mya

• Characteristics:

  • Spanning from the origin of trilobites to the end-Permian extinction.

  • Period Breakdown:

  • Cambrian

  • Ordovician

  • Silurian

  • Devonian

  • Carboniferous

  • Permian

Cambrian Period

• Formation of Gondwana: A significant southern landmass formed.

• Key Developments:

  • Origin of most major groups (phyla) of animals and many extinct groups.

  • Cambrian Explosion (540 mya): Rapid diversification of body plans.

Fossils

• Definition: Remains, impressions, or traces of living things from the past

• Types of Fossils:

  • Body fossils: remains like teeth, shells, bones

  • Cast fossils: when remains are replaced by minerals

  • Mold/ Impression fossils: 2D impressions or 3D molds of the body

  • Trace fossils: Evidence of activities (footprints, burrows)

  • Chemical fossils: Chemical evidence of past life

Cambrian Fossils

• Notable location: Burgess Shale (British Columbia)

  • Best-preserved Cambrian fossils including soft parts and impressions.

• Diversity: 25 out of 35 known animal phyla were present in the Cambrian.

Ordovician Period very

• Timeframe: ~485-444 mya

• Great Ordovician Biodiversification Event (GOBE):

  • Massive radiation of marine life.

  • Established biodiversity patterns for the remaining Paleozoic era.

• Major Organisms:

  • Molluscs, trilobites, green algae, early coral reefs, and the first fishes (sharks included).

Invasion of Land

• Late Ordovician: First land plants (bryophytes), fungi, and animals (trace fossils from sea scorpions) appeared.

Ordovician-Silurian Mass Extinction (first major mass extinction event and is the second largest)

• Cause: Possible onset of an ice age, anoxia, or gamma-ray burst.

• Impact: Marine diversity reduced by about half.

Silurian Period

• Timeframe: ~444-419 mya

• Characteristics:

  • Stability in marine and terrestrial environments.

  • Notable for the first bony fishes and land animal diversification (myriapods).

Devonian Period

• Timeframe: ~419-359 mya

• Marine Developments:

  • Origin of ammonites and various marine life including abundant sharks.

• Terrestrial Evolution:

  • Origin of tetrapods (early amphibians) and seed plants

  • Development of forests and soils.

Late Devonian Extinction (second major mass extinction) led to the decline of many marine and terrestrial species, paving the way for the rise of different ecosystems during the Carboniferous period.

• Timeframe: ~359 mya

• led to the decline of many marine and terrestrial species, paving the way for the rise of different ecosystems during the Carboniferous period. THIS IS WHERE WE STOPPED.

• Impact: 75% extinction of marine species due to anoxia.

Carboniferous Period

• Timeframe: ~359-299 mya

• Climate: Extensive glaciation, temperate regions across Gondwana.

• Key Developments:

  • Origin of “bark-bearing” trees leading to extensive coal deposits.

  • Emergence of reptiles and amniote eggs allowing transitions to dry habitats.

Permian Period

• Timeframe: 299-252 mya

• Supercontinent Pangea: Development led to major ecological shifts.

• Declining Diversity: General decline in marine invertebrates; dominance of conifers and synapsids occurred on land.

Permian-Triassic Mass Extinction

• Timeframe: 252 mya

• Significance: Largest extinction event (96% marine and 70% terrestrial species lost).

  • Causes speculated: volcanic activity, anoxia, and rapid climate changes.

Extinct Groups Post-Permian

• Major groups affected: Trilobites, giant arthropods, and many major vertebrate lineages.

Extinction Rates

• Differences:

  • Mass Extinction: Rapid and wide-reaching impacts on various taxa.

  • Background Extinction: Gradual processes resulting from environmental changes and competition.