THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Anoxia Lack of oxidized iron in the oldest sedimentary rocks. Urananite and pyrite are readily oxidized today, but are found unoxidized in Precambrian sediments Archean sedimentary rocks are commonly dark due to the presence of carbon, which would have been oxidized if oxygen had been present.

THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Anoxia Archean sedimentary sequences lack carbonate rocks but contain abundant chert, presumably due to the presence of an acidic, carbon dioxide-rich atmosphere. Carbon dioxide and water combine to form carbonic acid. In such an acidic environment, alkaline rocks such as limestone do not develop.

THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Anoxia Banded iron formations (BIF) appear in stratigraphic record in the Precambrian (1.8 - about 3 by).

THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Anoxia Banded iron formations (BIF) appear in stratigraphic record in the Precambrian (1.8 - about 3 by). They are cherts with alternating laminations of red oxidized iron and gray unoxidized iron. Origin of these BIFs is puzzling, and several possible explanations exist. May be related to hydrothermal vents (hot springs) in the sea floor.

THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Anoxia Bacteria may have played a role in the origin of BIFs. The simplest living organisms have an anaerobic metabolism. They are killed by oxygen. Includes some bacteria (such as botulism). Includes some or all Archaea, which inhabit unusual conditions Chemical building blocks of life could not have formed in the presence of O2 (amino acids, DNA)

THE PRIMORDIAL EARTH Hadean and Archean Eons Evolution of the Hydrosphere Ocean Formation - As the Earth cooled, H2O produced by out gassing could exist as liquid in the Early Archean, allowing oceans to form. Evidence - pillow basalts, deep marine sediments in greenstone belts.

THE PRIMORDIAL EARTH Hadean and Archean Eons Evolution of the Hydrosphere Oceans were originally freshwater (rain); may have been acidic from carbon dioxide and sulfurous gases in the atmosphere. Slow accumulation of salts derived from weathering (dissolution of soluble minerals). Ocean salinity is relatively constant today because surplus salts are precipitated at about the same rate at which they are supplied to the sea.

THE PRIMORDIAL EARTH Hadean and Archean Eons Evolution of the Hydrosphere Sodium remains in sea water due to its high solubility. Today Earth's water is continuously re-circulated through the hydrologic cycle

THE PRIMORDIAL EARTH Hadean and Archean Eons Formation of Atmosphere with Oxygen The development of an oxygen-rich atmosphere is the result of: 1. Photochemical dissociation - breaking up of water molecules into hydrogen and oxygen in the upper atmosphere caused by ultraviolet radiation from the sun (minor process) 2. Photosynthesis - the process by which plants produce oxygen (major process)

THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Free Oxygen Red sediments with iron oxide (red beds) appear in the stratigraphic record after the last appearance of the BIF (younger than 1.8 by).

THE PRIMORDIAL EARTH Hadean and Archean Eons Evidence of Free Oxygen Carbonate rocks (limestones and dolostones) appear in the stratigraphic record at about the same time that red beds appear.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Rock Types Granulites Highly metamorphosed gneisses (metamorphosed tonalites, granodiorites, and granites) and anorthosites (layered intrusive gabbroic rocks)

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Rock Types Greenstones Low-grade metamorphic minerals chlorite and hornblende produce green color. Mostly in trough-like or synclinal belts.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Rock Types Volcanics Volcanic (basaltic, andesitic, and rhyolitic) rocks with pillow structures (pillow basalts), indicating extrusion under water.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Rock Types Meta-sedimentary rocks Metamorphosed sedimentary rocks derived from the weathering and erosion of the volcanics. Metagraywackes, slates, schists, metaconglomerates (with granite pebbles), diamictites. Mostly deep water deposits.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Life The earliest evidence of life occurs in Archean sedimentary rocks.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Life Oldest direct evidence of life is in 3.5 by old Chert bed associated with Warrawoona Group western Australia Similar to cyanobacteria living today, which produce O2.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Life Stromatolites (cyanobacteria - blue-green algae) Also in rocks 2.8 - 3 by old - Pongola Group of southern Africa, and Bulawayan Group of Australia. More abundant later in Proterozoic rocks, but they are rare today.

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Life Algal filament fossils (filamentous prokaryotes) 3.5 b.y. at North Pole, western Australia

THE PRIMORDIAL EARTH Hadean and Archean Eons Archean Life Spheroidal bacterial structures (Monera) Fig Tree Group, South Africa 3.0 - 3.1 by cherts, slates, ironstones, and sandstones prokaryotic cells, showing possible cell division

THE PRIMORDIAL EARTH Hadean and Archean Eons The Origin of Life Most likely developed under anaerobic conditions O2 is poisonous to the construction of organic molecules No O3 layer to serve as protection from ultraviolet radiation

THE PRIMORDIAL EARTH Hadean and Archean Eons The Origin of Life Consequently life may have developed in water at depth below the surface of rocks

THE PRIMORDIAL EARTH Hadean and Archean Eons The Origin of Life Consequently life may have developed in the vicinity of black smokers (deep sea hydrothermal vents)

THE PRIMORDIAL EARTH Elements necessary to produce life: Hadean and Archean Eons The Origin of Life Elements necessary to produce life: Carbon Hydrogen Oxygen Nitrogen Phosphorus Sulfur

THE PRIMORDIAL EARTH Hadean and Archean Eons The Origin of Life Four essential components of life: Proteins (chains of amino acids linked together), used to build living materials and as catalysts in chemical reactions in organisms. Nucleic acids DNA RNA Organic phosphorus, used to transform light or chemical fuel into energy required for cell activities. A cell membrane to enclose the components within the cell.

THE PRIMORDIAL EARTH Hadean and Archean Eons The Origin of Amino Acids Lab experiments by Miller and Urey in the 1950's Formed amino acids from: H2 CH4 (methane) NH3 (ammonia) H2O (steam) and sparks (to simulate lightning)

THE PRIMORDIAL EARTH Hadean and Archean Eons Making Proteins Amino acids join together to make proteins. For them to join it requires: Input of energy Removal of water

THE PRIMORDIAL EARTH Hadean and Archean Eons Making Proteins Where do we get the energy and remove water? Heating from volcanic activity At lower temperatures in the presence of phosphoric acid. Evaporation Freezing Involve water in a dehydration chemical reaction On clays, which have charged surfaces, and to which polar molecules could attach On pyrite, which has a positively charged surface to which simple organic compounds can become bonded. Formation of pyrite yields energy which could be used to link amino acids into proteins

THE PRIMORDIAL EARTH Hadean and Archean Eons Making Proteins Proteinoids produced experimentally Film-like outer wall Capable of osmotic shrinking and swelling Budding similar to yeast Divide into daughter microspheres Aggregate into lines to form filaments, as in some bacteria Streaming movement of internal particles, as in living cells