CLIMATE AND LIFE NEW

• The earliest fossil is 3.55 Ga
• Stromatolites: Oldest 3.8 Ga. Formed by growth of layer upon layer of photosynthetic bacteria (cyanobacteria)
• Banded Iron Formations: Layers of haematite, oldest are 3.7 Ga, common between 2.4-1.9 Ga
• Great Oxygenation Event: When all available iron had been oxidised, atmospheric oxygen built up
• Eukaryotes appear ~1.8 Ga
• The Ediacaran fauna represents the oldest diverse set of multicellular, soft bodied organisms (565 Ma)

  
• Reasons for the Cambrian Explosion

  • Oxygen Levels
  • CaCO3 concentration
  • Precambrian extinctions
  • Arms race
  • Sea level
  • Development of hard parts
  • Preservation bias

  
• Almost every metazoan phylum known, with hard parts (and many that lack hard parts), appear in the Cambrian
• The Cambrian Explosion occurred within a time-span of ~40 million years
• Trace fossils also show an increased diversity in Cambrian rocks
• Development of new ecological niches and strategies (e.g. active hunting, deep burrowing, complex branching burrows)
• The diversity of the ocean is seen to increase over time. This diversity increase was associated by increasingly complex food webs and ecosystems
• Distinct evolutionary faunas


  • Cambrian Fauna
  • Palaeozoic Fauna
  • Modern Fauna
• Major problems for life invading the land

  • Support
  • Desiccation
  • Osmotic pressure in cells
  • Respiration
  • Photosynthesis
  • Vision & hearing
  • Food supply
  • Reproduction
• Evolution of plants is marked by 4 major events

  • Evolution of multicelled algae
  • The evolution of vascular tissue
  • The evolution of the seed
  • Evolution of flowering plants
• Arthropods were the first animals to invade the land (Silurian)
• Arthropods


  • Small with lightweight structure
  • Hard exoskeleton of chitin (structural support already in place)
• Size limitations of arthropods

  • Moulting
  • Open vascular system
  • No lungs (network of tracheae delivering oxygen by diffusion)
• Amphibians are tetrapods with two lifestyles- one in the water and one on land. They evolved from lobe-finned fish in the Late Devonian to early Carboniferous

  
• Similarities between lobe-finned fish and early amphibians

  • The four fins were skeletally similar
  • Their limbs were in the same position on their bodies
  • They both lacked claws or nails
  • The skull-morphology, the jawbone and teeth were very much alike
  • The teeth were both complex
  • Early amphibians still had a tail fin
  • Early amphibians still had traces of small bony scales on the skin

  
• Early amphibians


  • Still had a tail fin, suggesting they still spent a great deal of time in the water
  • Body shape and movement still resembled that of lobe-finned fish
  • Still had traces of small bony scales on the skin, a trait of fish

  
• Coelacanth


  • Once thought to have gone extinct more than 65 million years ago
  • Living forms were found in 1938 off the Comoros Islands, living between 150 and 300 m depth
  • Shared the oceans with trilobites and primitive molluscs
• Adaptations to life on land

  • Development of a skeletal girdle connecting the limb bones to the skeleton for better movement
  • More robust skeleton strengthening the vertebral column and rib bones, for extra support
  • Eyelids formed to help keep eyes moist
  • Development of a double circulatory system with a three-chambered heart
  • Tongue formed within its mouth, which could be used to catch prey
  • Ears adapted to detect sound waves through the thin medium of air
  • Skull became increasingly slender, with the temporal and opercular bones becoming smaller and the jaw bones becoming more fused together
• Even with new adaptations to terrestrial life, the early amphibians still had to remain close to a water source (and today they are reliant on it)
• They still used their skin for gas exchange, so they had to keep it moist to allow the transfer of oxygen and carbon dioxide
• They also had to lay their eggs in water, because without it their eggs would dry out, as they were only protected by a layer of jelly and not a shell
• The young would hatch into aquatic larvae with gills, and then undergo metamorphosis to develop into a terrestrial adult, able to walk on land
• It was not until the development of the amniotic egg that evolution proceeded to give rise to e.g. dinosaurs, birds and mammals
• Amniotic egg


  • Contains the Amnion or a sac which is fluid filled around the embryo during development
  • Contains a hard-outer shell
  • Contains a yolk sac
• Advantages of the amniotic egg

  • Hard-outer shell provided protection whilst remaining porous, allowing diffusion of oxygen and carbon dioxide
  • Yolk sac and albumin provided the embryo with food and water nutrients, eliminating the need for a larval stage
  • Amnion is the sac which is fluid filled around the embryo during development
• The amniotic egg is a significant feature in reptile evolution, as it allowed for life on land without the need for a water source in which to reproduce
• Diplodocus


  • Large herbivorous dinosaur
• Tyrannosaurus


  • Large carnivorous dinosaur
• Iguanodon


  • Herbivorous dinosaur
• Richard Owen in 1842 recognised that all dinosaurs belonged to one distinct group and decided to call this Dinosauria, meaning terrible lizard
• Dinosaurs evolved from Archosaurs, after the Permio-Triassic mass extinction
• First dinosaurs


  • Small bipedal carnivores appearing in the Triassic
• Dinosaur groups


  • Sauropods (herbivorous dinosaurs that appeared and radiated after the late Triassic)
  • Theropods (all carnivorous dinosaurs, diversified in the Jurassic and Cretaceous)
• Deinonychus


  • Human sized, agile and intelligent theropod dinosaur
  • Had a large claw on its hind foot, which it used to grab and cut open its prey
• Dinosaur hip patterns


  • Saurischia (where the pubis and ischium point in different directions)
  • Ornithischia (where the pubis has swung back and runs parallel to the ischium)