Earth Exact Age of Earth: _______. Geologic Dating Methods I: Radioactive Decay...
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Earth
Exact Age of Earth: _______
Geologic Dating Methods I: Radioactive Decay
http://www.btinternet.com/~j.doyle/SR/Emc2/decay_a-decay.gif
Geologic Dating Methods II: Known Rates of Radioactive Decay
http://people.hofstra.edu/j_b_bennington/2cnotes/halflife.JPG
Geologic Dating Methods III: Ratios of Parent : Daughter Atoms
Radiocarbon half-lifes
EARTH’S OLDEST ROCKS
4.03 BYA (Acosta Gneisses)3.7 – 3.8 BYA
3.4 – 3.5 BYA
http://pubs.usgs.gov/gip/geotime/age.html
3.4 – 3.6 BYA
Earth’s Oldest Known Rocks
(Probably do NOT date to Earth’s Formation)
Geologic Forces(e.g., Plate Tectonics)
Origin of Solar System
IRON METEORITES(Canyon Diablo)
Age: 4.53-4.58 BYA (U > Pb)http://pubs.usgs.gov/gip/geotime/age.html
Canyon Diablo Crater(Near Flagstaff AZ)
LUNAR ROCKS
Oldest Moon Rocks: 4.4-4.5 BYAhttp://pubs.usgs.gov/gip/geotime/age.html
Earth’s Origin (~ 4.5-4.6 BYA)
500 Million Years After Origin of Earth(Artistic Rendition)
http://www.arcadiastreet.com/cgvistas/earth/images/earth_ancient_volcano_600.jpg
The Earth Cools(Artistic Rendition)
http://www.cartage.org.lb/en/themes/Sciences/Paleontology/Paleozoology/Precambrian/Precambrian.htm
Ancient Evidence for Free Oxygen
• Isua Rock (Greenland): ~ 3.7 Billion Years Old• Metamorphosed Sediments• Abundant Free Uranium – Likely Only in
Oxidizing Environment
Oxygen Liberating Process?
Ancient Fossil “Cyanobacteria”(3.47 BYA)
http://marsfossil.home.netcom.com/images/pilbara_detail.jpg
Apex Chert in Western Australia (Pilbara Formation)
Fossil Stromatolites(3.5 BYA)
Living Stromatolites(Shark Bay Australia)
Fig. 2.8 in Willis and McElwain 2002
Stromatolite Formation
Living Stromatolites(Cross-Section)
Fossil Stromatolites (with Fossil Microorganisms)
Gunflint Chert – Ontario, Canada (2 BYA)
Origin of the Cell?
Origin of Organic Macromolecules?
Hypothesis I: Terrestrial Accretion
(Miller – Urey Experiments 1950s)
Origin of Cell Membrane?
Fig. 2.4 in Willis and McElwain 2002
Hypothesis: Drying, Rehydrating of Tide Pools
Hypothesis II: Meteoric and Cometary Infallof Organic Molecules formed Elsewhere
(Present Day Meterites can contain 1% Organic Molecules)
Hypothesis III: Meteoric and Cometary Infallof Cells formed Elsewhere (e.g., Mars)
Predominantly Non-Oxidized Sediments
Reduced Rocks
Ancient Evidence for Free Oxygen
• Isua Rock (Greenland): ~ 3.7 Billion Years Old• Metamorphosed Sediments• Abundant Free Uranium – Likely Only in
Oxidizing Environment
Banded Iron Formations (Up to 3.7-3.8 Billion Years Ago)
Evidence for Pulses of Free Oxygen
Red Beds(Up to 2.3 Billion Years Ago)
Evidence for Free Oxygen Accumulation
Heterocysts(Up to 2.1 Billion Years Ago)
Microbiology 155 (2009), 1418-1426
Atmospheric Oxygen Levels
http://ncbi.nlm.nih.gov
Fossil Eukaryotic Cells
Grypania ciliaris (Alga) in Northern Michigan
(2.1 – 1.1 BYA)
Fossil “Red Alga” in Arctic Canada(1200 MYA)
“Bangia”Figs. 2.12 in Willis and McElwain 2002
Fossil “Green Alga” in Spitsbergen(800-700 MYA)
“Cladophora”Fig. 2.14 in Willis and McElwain 2002
Fossil Tetrads(> 470 MYA)
Bitter Springs Formation, Australia
Cooksonia (420 MYA)