EPSC 201 Lecture Notes - Lecture 21: Proterozoic, Photochemistry, Photosynthesis
26 Jan 2017
School
Department
Course
Professor
Document Summary
Late-heavy bombardment of earth and its moon by meteorites 4. 0-3. 85. Ga, dest(cid:396)o(cid:455)ed (cid:374)ea(cid:396)l(cid:455) all of ea(cid:396)th"s surface: a time of significant change to planet earth, time between 3. 85 and 2. 5 ga. Early crust was probably made up of mafic igneous rocks formed as island-arcs and hot-spot volcanoes. Partial melting of basaltic crust created felsic rocks. Small blocks of buoyant crust were created. Erosion produced sediment: proto-continents were formed by collisions of buoyant blocks. Volcanic arcs, hotspots and sedimentary debris were sutured together as the first continents. End of archean, continental crust reached around 85% of present area: first life. Around 3. 2 ga oldest undisputed fossils. Shapes in rocks indicate organisms as old as 3. 4-3. 5 ga. Possibly as old as 3. 8 ga (even older) Photosynthesis occurring by late archean: origins remain uncertain. Probably from deep, dark submarine hot-water vents (cid:862)(cid:271)la(cid:272)k s(cid:373)oke(cid:396)(cid:863) Thermophilic (heat-loving) bacteria or archaea existed in extreme conditions. Oldest life on earth: bacteria 3. 5 billion years, modern cyanobacteria (algae)
