Lecture 1 History Of Life On Earth Flashcards
Current atmospheric oxygen
20% O2 essential for many eukaryotic organisms
Precambrian
First invertebrates 700 million years ago
Permian 286-248 million years ago
followed by decrease of atmospheric O2 and lowest sea levels leading to large extinction
Hadean 3800 MYA
Harsh high temp, CO2 and volcanic activity 🌡️🌬️🌋
No evidence of live but basic chemicals available
Formation of complex organic molecules capable of replication and protein assembly e.g. nucleic acids
Archaean 3800-2500 MYA
A few small islands form but Earth is still mainly oceanic. Cooling, high CO2 negligible O2. First prokaryotic cells. Photosynthetic bacteria produce O2 and large cyanobacterial mats trap sediments forming rock like stromatalites.
O2 for ATP synthesis oxidises iron benefitting aerobes
Proterozoic 2500-542 MYA
O2 buildup further allowing oxidisation
~1500 MYA marine eukaryotes appear & diversify
End of proteozoic 635 MYA evidence of complex multicellular marine animals - bilateral soft bodied and poorly conserved as lacking hard structures
Cambrian explosion 488-542 MYA
O2 conc approaches current level
Continents come together form land mass.
Rapid animal diversification - almost exclusively marine: worms, molluscs, arthropods
Evolution of predators stimulates arms race to harden for protection and develop bilateral symmetry for movement
Ordovician 488-444 MYA
Increase in molluscs, cephalopods trilobites and echinoderms
Continued marine evolution v. Little change in land/freshwater no multicellular land plants
End of orvician mass extinction, 75% of all species as glaciers form over Godwana and sea levels drop + water cools
Silurian 444-416 MYA
Marine life rebounds
Marine vertebrates e.g. jawless fish
First terrestrial vascular plants
First terrestrial arthropods - scorpions and millipedes
Swamps
Devonian 416-359 MYA
North Laurasia moves towards south Godwana
Coral, shelled cephalopods and jawed fish
All current major groups present by end of Devonian period
Fish up to 10cm long
Evolution of terrestrial plants - club moss, horsetail, tree fern and forest soil develops, wind pollinated seed plants
Fossils of centipedes, spiders and mites
Walking fish
75% extinction end of era
Carboniferous 359-397 MYA
Climate warming
Swamp forest petrified to coal
Excess O2
Arthropods and vertebrate reptiles evolve
Permian 297-251MYA
Continents coalesce to form Pangaea
Diverse fauna evolve including reptile ‘amniotes’ that lay well protected (shelled) this lineage leads to mammals
Deterioration of life due to volcanic activity reducing O2 and ash blocks sunlight leading to cooling and glaciers
96% extinction of fauna
Mesozoic: period 251-65MYA:
251-200 MYA
New seed bearing plants
Pangaea separates into continents
Sea levels rise reflooding continental shelf forming inland seas
O2 levels rise
Life diversifies differently on each continent
Mesozoic: Triassic 251 - 213 MYA
Spread of marine & freshwater animals
Amniotes diversify to crocodiles, dinosaurs* and mammals
*Dinosaurs are characterised by upright posture and are only one subgroup of ancient reptiles - did not include many reptiles despite their ‘saur’ nomenclature e g. Icthyosaur, plesiosaur and pterosaur are not dinosaurs
End of Triassic period mass extinction due to meteor
Mesozoic: Jurassic 200-145MYA
Dinosaur reptiles diversify to quadraped herbivores and biped carnivores (w/some biped herbivores)
Pterosaur flight likely to have been weak required vantage points for takeoff (uplift)
Bird flight may have evolved secondarily utilising feathers evolved for insulation
