GEOS 1004 Lecture Notes - Lecture 17: Water Cycle, Continental Crust, Hematite
8 Mar 2018
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Lecture 17: history of the earth"s surface; hydrologic cycle. Given off as a gas during volcanism; +co2 and n2 (create atmosphere), not h2 (escapes to space). First record of water - first sedimentary rocks; 4. 0 b. y. ago. Landmasses emerge gradually ~3. 0 b. y. ago due to plate tectonics (making of continental crust). Between 4. 0-3. 0 b. y. , there is no land- earth is covered by continuous ocean: atmosphere. Initially dominated by co2, h2o, methane, ammonia due to volcanism. Anerobic photosynthesis by the earliest life = cyanobacteria. 2. 5 b. y. ago - oxygen begins to accumulate. 1. 0 b. y. ago - oxygen levels approach today"s. The early ocean was reducing (cid:523)(cid:498)ferrous(cid:499) iron, fe2+, which is soluble). Later the ocean became oxidizing (fe is ferric, fe3+, which is insoluble). Banded iron formations = chemical sediment, iron oxide (hematite), precipitated when oceans became oxygen rich. 2. 5 billion years ago = 50 c since then varies 5 -30 c: climate. Sun burns hotter today than 4 b. y. ago (~30%).
