by: Charles O’Dale
On this planet, impact craters are divided into basic morphologic subdivisions:
- simple: The transition size between simple to complex craters is 2km in sediments and 4km in crystalline rocks (Dence 1972).
- complex: The transition size between complex to ringed basin craters is 10 to 50 km (Osinski, G. 2008).
- peak ring: With increasing diameter, impact structures become proportionately shallower and develop more complicated rims and floors, including the appearance of central peaks and interior rings.
- Multi-Ring Crater: Sudbury is a possible example.
The transition size between simple to complex craters is 2km in sediments and 4km in crystalline rocks (Dence 1972). The transition size between complex to ringed basin craters is 10 to 50 km (Osinski, G. 2008). With increasing diameter, impact structures become proportionately shallower and develop more complicated rims and floors, including the appearance of central peaks and interior rings. While a single interior ring is required to define a basin, basins have been subdivided, with increasing diameter, on other planetary bodies, into central-peak basins, with both a peak and ring; peak ring basins, with only a ring; and multi-ring basins, with two or more interior rings (Wood and Head 1976). It is not known if there are examples of true multi-ring basins equivalent to those observed on the moon on Earth (Grieve 2006). A possible exception to this may be the Hudson Bay Arc, also known as the Nastapoka Arc, which I describe in a later article.
- Simple Crater
A simple crater is a “transient” crater that has kept its bowl shape after the impact with minor slumping.
- Complex Crater
The central peak of the complex crater is formed as a result of uplift of material beneath the crater. Complex craters on Earth first occur at diameters greater than 2 km in layered sedimentary target rocks but not until diameters of 4 km or greater in stronger, more coherent, igneous or metamorphic, crystalline target rocks (Dence 1972).
Lake Mistastin impact structure with a diameter of 28 kilometres is a ‘central peak basin’ structure.(French 1998)
The exposed core of uplifted rocks in complex meteorite impact craters. The central peak material typically shows evidence of intense fracturing, faulting, and shock metamorphism.
CENTRAL UPLIFT: Structural elevation (central peak) in complex impact structures. Originates from elastic rebound and transient-crater collapse in the modification stage of impact cratering.
There are examples of complex impact structures with central uplift on Earth, e.g., the Steinheim Basin in Germany or Jebel Waqf as Suwwan in Jordan; the latter is eroded by some tens to hundreds of meters but still exhibits the classical smashing morphology (Schmieder 2010). Since these craters are a bit “out of range” of my airplane, I will use the lunar crater Tycho as a complex crater example.
- Peak Ring Crater
Anther peak ring basin on Earth is Ries crater (crater diameter 24 km, diameter of the crystalline ring 12 km), the ring is not visible very well due to the Ries lake sediments that cover large parts of the crater. It is a major structural feature that outcrops, e.g., beneath Nördlingen city.(Schmieder 2010)
- Multi-Ring Crater
CRATER SIZE vs PLANET/MOON
CRATER vs SIZE OF METEOROID
The cosmic projectile, meteoroid, asteroid, comet, or other celestial object which causes an impact event. The kinetic energy of an object of mass m traveling at a speed v is = mv2/2, provided v is much less than the speed of light.
The origin and emergence of life under impact bombardment (Cockell 2006)
Craters formed by asteroids and comets offer a number of possibilities as sites for prebiotic chemistry, and they invite a literal application of Darwin’s ‘warm little pond’. Some of these attributes, such as prolonged circulation of heated water, are found in deep-ocean hydrothermal vent systems, previously proposed as sites for prebiotic chemistry. However, impact craters host important characteristics in a single location, which include the formation of diverse metal sulphides, clays and zeolites as secondary hydrothermal minerals (which can act as templates or catalysts for prebiotic syntheses), fracturing of rock during impact (creating a large surface area for reactions), the delivery of iron in the case of the impact of iron-containing meteorites (which might itself act as a substrate for prebiotic reactions), diverse impact energies resulting in different rates of hydrothermal cooling and thus organic syntheses, and the indiscriminate nature of impacts into every available lithology—generating large numbers of ‘experiments’ in the origin of life.
Theories on the pathways of prebiotic evolution and the formation of the first complex self-replicating macromolecules have to take into account several common requirements, including: (i) a source of energy to drive molecular and macromolecular synthesis, (ii) a mechanism for the localized concentration of reactants to favour the required chemical reactions, (iii) suitable catalysis and (iv) a suitable geochemical environment for these reactions and their products to be sustained for sufficiently long periods to lead to the origin of life.