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)