Carters On Earth

Impact Craters on Earth

Frequency of Impacts

• Earth experiences approximately 10 times more frequent impacts than the Moon.
• The number of craters with diameters greater than 20 km varies across different celestial bodies:
  • Venus: 31
  • Earth: 21
  • Mars: 14
  • Mercury: 10,000+
  • Moon: 1000+

Gravitational Focusing

• The concept of gravitational focusing influences impact rates.

Cascadia Subduction Zone

• The Cascadia Subduction Zone presents various types of seismic activities:
  • Crustal earthquakes (e.g., AD 900, 1872).
  • Subduction zone earthquakes (e.g., AD 1700).
  • Deep earthquakes (e.g., 1949, 1965, 2001).

Distribution of Impact Craters

• There are 190 known impact craters on Earth.
• Distribution across continents:
  • Asia & Russia: 31 craters (16% of Earth's land area)
  • Africa: 20 craters (20% of Earth's land area, 11% of known craters)
  • North America: 60 craters (16% of Earth's land area, 32% of known craters)
  • South America: 11 craters (12% of Earth's land area, 6% of known craters)
  • Antarctica: 0 craters (9% of Earth's land area)
  • Europe: 41 craters (7% of Earth's land area, 22% of known craters)
  • Australia: 27 craters (6% of Earth's land area, 14% of known craters)

Confirmed Impact Structures in the United States

• Approximately 28 confirmed impact structures exist in the United States.
• Examples of impact structures, including location, diameter, and age:
  • Haviland, Kansas: Diameter = $0.015$ km, Age < $0.001$ Ma
  • Odessa, Texas: Diameter = $0.168$ km, Age < $0.050$ Ma
  • Meteor Crater (Barringer), Arizona: Diameter = $1.19$ km, Age = $0.049 \,\pm\, 0.003$ Ma
  • Newporte, North Dakota: Diameter = $3.2$ km, Age < $500$ Ma
  • Flynn Creek, Tennessee: Diameter = $3.8$ km, Age = $360 \, \pm \, 20$ Ma
  • Glasford, Illinois: Diameter = $4$ km, Age < $430$ Ma
  • Decaturville, Missouri: Diameter = $6$ km, Age < $300$ Ma
  • Middlesboro, Kentucky: Diameter = $6$ km, Age < $300$ Ma
  • Rock Elm, Wisconsin: Diameter = $6$ km, Age < $505$ Ma
  • Santa Fe, New Mexico: Diameter = $6-13$ km, Age < $1200$ Ma
  • Cloud Creek, Wyoming: Diameter = $7$ km, Age = $190 \, \pm \, 30$ Ma
  • Crooked Creek, Missouri: Diameter = $7$ km, Age = $320 \, \pm \, 80$ Ma
  • Wetumpka, Alabama: Diameter = $7.6$ km, Age = $83$ Ma
  • Des Plaines, Illinois: Diameter = $8$ km, Age < $280$ Ma
  • Glover Bluff, Wisconsin: Diameter = $8$ km, Age < $500$ Ma
  • Serpent Mound, Ohio: Diameter = $8$ km, Age < $320$ Ma
  • Calvin, Michigan: Diameter = $8.5$ km, Age = $450 \, \pm \, 10$ Ma
  • Red Wing, North Dakota: Diameter = $9$ km, Age < $95$ Ma
  • Upheaval Dome, Utah: Diameter = $10$ km, Age < $170$ Ma
  • Avak, Alaska: Diameter = $12$ km, Age < $100$ Ma
  • Wells Creek, Tennessee: Diameter = $12$ km, Age = $200 \, \pm \, 100$ Ma
  • Marquez, Texas: Diameter = $12.7$ km, Age = $58 \, \pm \, 2$ Ma
  • Kentland, Indiana: Diameter = $13$ km, Age < $33$ Ma
  • Sierra Madera, Texas: Diameter = $13$ km, Age < $97$ Ma
  • Ames, Oklahoma: Diameter = $16$ km, Age = $470 \, \pm \, 30$ Ma
  • Manson, Iowa: Diameter = $35$ km, Age = $73.8 \, \pm \, 0.3$ Ma
  • Beaverhead, Idaho, Montana: Diameter = $60$ km, Age = $600$ Ma
  • Chesapeake Bay, Virginia: Diameter = $90$ km, Age = $35.5 \, \pm \, 0.3$ Ma

Tectonic Provinces

• Various tectonic provinces are identified, including INNUITIA, CALEDONIDES, KETILIDIAN, ORTH ATLANTIC, CHUR, RINKIAN, NVI, MLE, WYOMING, CENTRAL MAZATZAL, SOUTHWEST PROVINCE, PLAINS, UPE, SOUTHERN VOR, OUACHITA, MAKKOVIK.
• Geologic time periods and associated orogenies are classified as:
  • TERTIARY TO RECENT (Eurekan, Cascadian)
  • CRETACEOUS TO TERTIARY (Laramide)
  • JURASSIC TO CRETACEOUS (Columbian)
  • JURASSIC (Sonoman)
  • PALEOZOIC (Late (Alleghanian, Antler), Middle (Acadian, Ellesmerian), Early (Taconian))
  • PROTEROZOIC (Late to Cambrian (Avalonian), Middle to Late (Grenvillian), Early to Middle (Central Plains), Early (Hudsonian))
  • ARCHEAN CRATONS (Kenoran)

Impact Signatures

Meteorite Fragments

• Presence of meteorite fragments around a feature serves as strong evidence of an impact event.
• Examples:
  • Meteor Crater, AZ: Size = $1.2$ km, Age = $50,000$ yr
  • Odessa Crater, TX: Size = $168$ m, Age = $50,000$ yr
  • Haviland Crater, KS: Size = $15$ m, Age < $1,000$ yr

Shock-Metamorphic Effects

• Extreme physical conditions (pressure, temperature, and strain) from shock waves produce unique effects in rocks and mineral grains.
• These effects are distinct from normal geological deformation and are accepted as unique products of impact events.

Shatter Cones

• Distinctive cone or fan-shaped features in rocks with radiating fracture lines.
• Formed due to high pressure, high velocity shock waves produced by a large impacting object or explosion.
• Found in:
  • Nuclear test sites
  • Meteorite impact structures
• Example: Sierra Madera, Texas (Size: 13 km, Age: < 100 Myr)

Wells Creek, TN

• Size: 12 km
• Age: ~200 Myr

Serpent Mound, OH

• Size: 8 km
• Age: ~320 Myr

Shocked Quartz

• Under intense pressure, the crystalline structure of quartz is deformed along planes inside the crystal.
• Quartz is ideal for identifying shock metamorphism because:
  • It is abundant in a wide range of rocks.
  • It is stable over long periods.
  • It resists change by alteration and metamorphism.
• Found in:
  • Nuclear test sites
  • Meteorite impact structures
  • Lightning strikes

Coesite and Stishovite

• Coesite is a high-pressure polymorph of $SiO_2$.
• Stishovite is another high-pressure polymorph of silica.
• The type of deformation depends on shock pressure.
  • Undulatory extinction.
  • Mosaicism.
  • Planar fractures (0001) and {1011}.
  • Feather features.
  • Planar deformation features {1013}/{1012}.
  • Diaplectic glass.
  • Lechatelierite.

Upheaval Dome, UT

• Size: 10 km
• Age: ~170 Myr

Impact Breccia

• Rock composed of broken fragments of minerals, rocks, or even other pieces of breccia.

Decaturville, MO

• Size: 6 km
• Age: < 300 Myr

Surface Expression

• Many impact structures have no features visible from the ground and thus have no surface expression.

Manson Crater, IA

• Size: 35 km
• Age: 73.8 Myr
• An unusual sequence of rocks encountered in 1912 yielded the only naturally soft groundwater known in Iowa.
• Hard water is formed when water percolates through deposits of limestone.
• There is evidence that some process vaporized the underground Limestone layers in an area of about 30 km around the town of Manson.

Dinosaur Extinction

• Dinosaur extinction occurred approximately 66 million years ago.
• The Manson Impact occurred around 74 million years ago.

Red Wing, ND

• Size: 9 km
• Age: 200 Myr
• It has been suggested that the Red Wing crater may have been part of a multiple impact event which also formed the Rochechouart crater in France, Saint Martin crater in Manitoba, Obolon' crater in Ukraine, and the Manicouagan crater in Quebec.

Tektites

• Natural glass formed from debris ejected during an impact event.
• Near-surface materials were melted and ejected from a crater, forming small bodies of molten material that rapidly cooled upon re-entry into the atmosphere.

Chesapeake Bay, VA

• Size: 90 km
• Age: 35.5 Myr

Completeness of Impact Crater Discovery

• Small craters are destroyed faster than larger ones.
• Impact craters are still being discovered.