Lecture 3 Past Geographies: Centres of origin and dispersal: - Plate tectonics reveals ancient continental configurations - Ocean floor banding indicates past positions of continents back to 180Mya - Older continental configurations not visible in ocean floor banding (all older bands have been consumed) - Paleomagnetic evidence helps reconstruct older continental configurations - rock is still molten, before it solidifies the magnetic minerals in the rock will orient themselves towards the pole. A is an example of the Mid Atlantic Ridge - the old spreading zones become further apart. ERA PERIOD Quaternary EPOCH Holocene epoch: 0.1-0 mya Pleistocene epoch: 2.5-0.1 mya 2.5-0 mya AGE RANGE Sea floor spreading bands become offset by transverse faults. Magnetic orientation of crystallized minerals shows their alignment in relation to magnetic poles CENOZOIC Neogene Pliocene epoch: 5-2.5 mya Miocene epoch: 23-5 mya 25-2.5 mya Paleogene 65-24 mya Cretaceous 146-65 mya MESOZOIC Jurassic 208-146 mya Triassic 245-208 mya Permian 280-245 mya Carboniferous 360-280 mya 10 mya 7 mya 5 mya Devonian 408-360 mya PALEOZOIC Silurian 438-408 mya Ordovician 505-438 mya Cambrian 540-500 mya PRECAMBRIAN 4.5 billion to 540 mya Earliest life: all at sea: Modern sea floor 3 mya Plate A Plate Pattern of magnetic variations associated with oceanic ridges, developed as new ocean floor was added to the oceanic crust at the ridge spreading center D.78 Magnetic epoch Brunhes Matuyama Gauss 2.59 Vertical sequence of basalt flow on continent - Planet Earth formed around 4.5 billion years ago. - The first evidence of life on earth were one-celled marine alga, Grypania, which dated to 3.4 billion years ago. Precambrian Life: - From 3.4 billion to 544Mya. - Only marine life existed - but even so there is no evidence of life from 4,500 till 3,400 when one-celled life began to be recorded as fossil - still there is little evidence of such life. - Mainly primitive, one-celled or multi-celled but were lacking in shells - were soft-bodied organisms so there is very little fossil evidence as they tended to decompose. - The Precambrian era represents about 89% of Earth history - We will focus on about the last ft% in depth. Middle Silurian 425 Ma Earliest evidence of terrestrial life: PANTHALASSIC OCEAN North China - By Silurian (435-410Mya): complex terrestrial life first appeared Sitona Kazakstanla - North America and Northern Europe joined in one landmass: known as Euramerica. PALEO-TETHYS OCEAN Chirohte Chifla RHEIC - Most other land masses were joined in supercontinent of Gondwana. OCEAN IAPETUS OCEAN GONDWANA 0 O 1997 C.R. Scotese
- During the Silurian, there was one world ocean. - Most of the land mass was situated in the Southern Hemisphere. - Gondwana was the dominant landmass - Silurian life on sea and land: nautiloid cephalopod lived in the sea and the trees had no leaves (more ecologically complex) so instead the stems were green and photosynthesised - e.g. horsetail plants which have no leaves. Devonian World: - Two main land masses: Gondwana and Euramerica. - Most of the land masses are