History Of Life

Early Earth

  • Earth formed approximately 4 billion years ago (BYA).

  • Conditions:

    • Mix of water vapor, carbon dioxide (CO2), methane, ammonia.

    • Surface was hot and molten (Hadean Era); no solid rocks.

  • Formation of liquid water likely occurred early, though it was rich in iron.

Oparin-Haldane Hypothesis

  • Early Earth had necessary conditions to build organic molecules which includes:

    1. Synthesis of simple organic molecules.

    2. Synthesis of macromolecules.

    3. Assembly of 'protocells'.

    4. Origin of cell replication.

Eons and Eras

  • Understanding the timeline of Earth's history:

    • Hadean Eon: 4.6-4.0 BYA

      • Characterized by molten surface; no rocks.

    • Archean Eon: 4.0-2.5 BYA

      • First evidence of life: Stromatolites, dating back to 3.5 BYA.

      • Arche means "ancient".

Proterozoic Eon

  • Timeframe: 2.5 BYA to 542 million years ago (MYA).

  • Significant events:

    • Beginning of atmospheric oxygen levels rising possibly due to photosynthetic bacteria.

    • Origin of Eukaryotic Cells (2.1 BYA) through endosymbiotic theory, where mitochondria and chloroplasts were formed from prokaryotes living inside eukaryotic cells.

    • Lynn Margulis proposed the endosymbiotic hypothesis.

  • Ediacaran Period (575-535 MYA): Rise of multicellular eukaryotes at the end of Proterozoic.

    • Organisms were typically soft-bodied.

Phanerozoic Eon

  • Covers 542 MYA to present.

  • Main Eras:

    • Paleozoic: 542-251 MYA

    • Mesozoic: 251-65.5 MYA

    • Cenozoic: 65.5 MYA to present.

Paleozoic Era

  • Cambrian Period (542-488 MYA):

    • Cambrian explosion marked a significant increase in species diversity and disparity in body plans.

    • Every animal phylum present today existed, along with some that are now extinct.

    • Increase in oxygen levels; evolution of bilateral symmetry and hard body structures.

    • Important Cambrian animals:

      • Trilobites.

      • Opabinia.

      • Anomalocaris.

      • Hallucigenia.

      • Pikaia (oldest known chordate).

  • Ordovician Period (488-423 MYA):

    • Appearance of ostracoderms (armored jawless fish).

  • Silurian Period (423-416 MYA):

    • Development of freshwater jawless fish.

    • Evidence of terrestrial life (fungi, arachnids, centipedes).

  • Devonian Period (416-359 MYA):

    • Appearance of placoderms and ferns.

    • First tetrapods (chordates that moved to land).

  • Carboniferous Period (359-299 MYA):

    • Divided into Mississippian and Pennsylvanian.

    • Polar ice caps led to sea level drops, increasing terrestrial habitats.

    • Formation of vast swamp forests; fossil fuels created in swampy areas.

    • Diversification of ray-finned fishes and tetrapods; origin of amniotes (reptiles, birds, mammals).

  • Permian Period (299-251 MYA):

    • Reptiles diversified.

    • Dominance of gymnosperms (pines, cycads, ginkgos).

Permian-Triassic Extinction

  • Marked the end of Paleozoic Era and start of Mesozoic.

  • This mass extinction led to the demise of about 90% of species, including trilobites and many fish species.

  • Possible causes:

    • Volcanic activity leading to climate change.

    • Increase in methanogenic bacteria producing methane, exacerbating climate crises.

Mesozoic Era

  • Timeframe: 251-65.5 MYA.

  • Triassic Period:

    • Survivors of the extinction diversified; early dinosaurs and the first mammals appeared.

  • Jurassic Period:

    • Extensive diversification of dinosaurs (e.g., Sauropods and Stegosaurs).

    • In the sea, plesiosaurs thrived; in the air, pterosaurs dominated.

    • Origin of birds from ancient fin or wing structures.

  • Cretaceous Period (145-63.3 MYA):

    • Continued diversification of dinosaurs (e.g., Tyrannosaurus rex, Velociraptor).

    • Origin of flowering plants.

Cretaceous/Paleogene Extinction

  • The second largest extinction event, with approximately 80% of species going extinct, including non-avian dinosaurs.

  • Hypothesized causes include:

    • Impact from space objects leading to climate changes.

    • Evidence of an impact crater located in the Yucatan Peninsula; explained by Adriana Ocampo.

Cenozoic Era

  • Timeframe: 65.5 MYA to present.

  • Paleogene Period (65.5-23 MYA):

    • Survivors of the earlier extinction diversified, leading to the emergence of mammals, birds, flowering plants, and pollinating insects.

  • Neogene Period (23-2.6 MYA):

    • Appearance of hominins (human ancestors, not modern humans).

  • Quaternary Period (2.6 MYA-Present):

    • Homo sapiens appeared about 200,000 years ago.

    • La Brea tar pits show evidence of animals existing around 10,000 years ago.