asteroid impacts on earth

see also:

• a brief history of the World
• How Australia evolved in geological terms and evolution
• evolution
• evolution of bacteria
• Prehistoric times
• observing and photographing meteors

• asteroid and comet impacts on earth have had major implications for both creating life on earth and in causing mass extinction events
• NEO's > 2km diameter (1 million megatons energy) would create an impact winter with loss of crops worldwide & subsequent starvation & disease. These strike earth once or twice every million years.
• NEO's > 15km diameter (100 million megatons energy) would cause a mass extinction event as occurred in 65mya which wiped out the dinosaurs
• there are ~1000 NEA (near earth asteroids) larger than 1km & perhaps a million larger than 50m and max. size is some 25km.

• c4,500mya formation of Earth arose after its collision with a Mars-sized impactor planet “Theia”, which resulted in the formation of Earth’s moon and its remnants remain as two large low-velocity provinces (LLVPs), in the lowermost mantle beneath Africa and beneath the Pacific Ocean ¹⁾
• 4450-4000mya solidification of earth's crust (protocrust) and the formation of earth's hot interior due to the collision of ice and metallic asteroids / meteors
  • This early event probably only delivered half the water we currently have today - the rest is thought to have come from later bombardments of comets.
• some believe that the prolonged ensuing metallic hailstorm ripped oxygen atoms from water producing hydrogen which formed a hydrogen rich atmosphere conducive to creating life molecules and lasting 200 million years before dissipating into space, and the free oxygen radicals then combined with iron to form ferric oxide ²⁾

• c3800 mya: the Late Heavy Bombardment of meteors ends
• c3500 mya: 20-30km diameter asteroid hits Marble Bar in Western Australia creating massive global earthquakes, tsunamis, tectonic plate shifts ³⁾

• 2,229mya: the 70km wide Yarrabubba impact crater in Western Australia the result of an asteroid impact which is thought to have helped end the “snowball earth” period
• 2000mya: Vredefort asteroid impact crater Sth Africa - at 20-25km asteroid size (double the height of Mt Everest!) one of the largest since the Hadian era
• 580mya massive Acraman impact crater, Gawler Ranges, Sth Australia which had fall out ~4“ thick layer of pink rhyolite ejectiles in the Flinders Ranges 300km to the east - now a salt lake / salt pan
  • bolide diameter 4.8km; velocity 25km/sec; energy 5.2 x 10^6 Mt TNT; transient cavity 40km; collapse crater 90km; ejecta blanket >540km;
• 541mya possible 600km wide massive asteroid impact in Central Australia, SW of Alice Springs - Massive Australian Precambrian-Cambrian Impact Structure (MAPCIS) if confirmed it would the largest known such impact on earth and beating the other largest - Deniliquin, and could have played a major role in the subsequent Cambrian explosion of life on earth - see https://www.youtube.com/watch?v=RHlov3BeLAY

• c358-372mya Woodleigh Crater in Western Australia
  • could have been a 5-6km diameter asteroid - 4th largest since Hadean era causing megatsunamis, volcanism in Victoria, global forest fires, volcanic winters, brief glaciation event and could have triggered the global Devonian extinctions due to mass plankton die off and disruption of the food chain
  • c372mya: Frasnian-Fammenian extinction event 50% of genera and 90% of families become extinct and was followed by a glaciation event
• 360mya: Hangenberg extinction event lasting 100,000-300,000yrs due to profound oceanic anoxia and which would result in crude oil deposits forming
  • this could have been triggered by the dual East Warburton impact craters in central Australia dated at 300-360mya which again increased volcanic eruptions in Victoria
• 250mya: it is now thought by many that the end of the Permian age (ie. before dinosaurs) was due to a NEO which hit earth and plunged earth into darkness & freezing cold, caused volcanoes & released hydrogen sulphide gas, wiping out 90% of sea life & 80% of land life globally - the “Great Dying” in addition to setting off the separation of the continents from the unified Gondwana land mass a 150m yrs later. The possible sites are either:
  • Wilkes land region of east Antartica - 483km wide crater hidden more than 1.6km beneath the Antartic ice sheet and has a 321km wide plug of mantle - a mascon. The rift between Antartica and Australia passes directly through this crater. (published 2006)
  • offshore from NW of Western Australia when it was part of Pangaea resulting in the Bedout High underwater crater which is buried beneath thousands of meters of rock (discovered by oil drilling samples). The meteor is estimated to have been at least 10km diameter, leaving an impact crater of 200km diameter.
• 130mya: Gosse's Bluff NT, Australia meteorite impact crater 20-25km wide (now 6km wide)
• 65-66mya: global mass extinction event when 75% of animal species died out including all the dinosaurs - this is now confirmed to be due to a NEO asteroid of 15km diameter (100 million megatons energy) hitting Chicxulub on Mexico's Yucatan peninsula where it created a 200km crater. There had been a preceding increased volcanic activity in the Deccan which was in fact responsible for a brief warming phase 200,000 years before the mass extinction, but this had no long-term effect on life and the climate.
• 43-46mya: asteroid impact creates the Silverpit crater under the North Sea
• 26-38mya: major extinction event - all five mammal groups suffered huge losses around the Eocene-Oligocene boundary after Earth’s climate shifted from swampy to icy resulting in the loss of over 60% of Afro-Arabian mammalian species.
• ~5mya - a nearby star (within 90 light years) goes supernova sprinkling Earth with a thin layer of Fe60, an iron isotope produced only by supernova detonations, and many UV-sensitive marine plants and animals died.
  • these two back-to-back nearby supernovae at end of pliocene may have tripled radiation doses for thousands of years due to a 20-fold increase in high energy muon particles striking earth and this may have increased rate of DNA mutations and thus the rate of evolution ⁴⁾
• 50,000 years ago meteor crater in Arizona by an estimated 30m diameter iron meteorite
• c10,800BC: Abu Hureyra, Syria destroyed at the Younger Dryas Onset ⁵⁾
  • megafauna and Clovid paleoindian culture extinction event - the existence of mammoths, mastodons, horses, camels, dire wolves, American lions, short-faced bears, sloths, and tapirs terminated abruptly at the Allerød-Younger Dryas boundary
    • causes may be:
      • significant reduction or shutdown of the North Atlantic “Conveyor”
      • result of a stream of comet impacts on the Arctic ice cap, melting the Laurentide ice sheet, although this seems to be rejected by scientists at present as there is apparently no geological evidence of comet impacts but then there probably wouldn't be if they hit the ice cap, and this may be a case of premature closure of an hypothesis ⁶⁾
        • this massive sudden flooding event could also explain the Scablands of NW USA
        • this would be supported by Zorastrian beliefs “serpent in the sky” and similar beliefs across the globe with most megalithic structures of around 9600BC around the world (Malta, Göbekli Tepe in Türkiye, Indonesia, America eg. Serpentine Mount, and in Mexico) demonstrating astronomic features and prominent serpents, often depicted as falling from the sky
        • the sequential comet impacts theory is also supported by the widespread finding across Nth America and Europe of a black carbon, cubic diamond nanoparticles, and iridium rich “extinction” black mat boundary layer dated to 10,800BC with fossils of Rancholabrean megafauna below it but none above it other than bison and nor is there evidence of Clovis paleoindian culture artefacts in Nth America in or above this black mat.
• c1600BC: ancient Middle Eastern city now called Tall el-Hammam destroyed and the walls of Jericho blown down and may have been the biblical city of Sodom ⁷⁾
• 1908 Siberian meteor impact with energy of 15 megatons and it's airburst at an altitude of 5-10km destroyed 80 million trees over an area of 2150 sq. km - enough to easily wipe out a major city. Such NEO's hit earth once every 200 yrs on average.