Meteorite Impacts and Crater Formation

Meteorite Impacts

• Meteorite impacts create craters of varying sizes.
• Simple craters are less than 2 km in diameter and form from smaller impacts.
• Complex craters are greater than 2 km in diameter and form from larger impacts.
• Impacts cause various effects including shock waves, vaporization of materials, and ejection of material.

Crater Formation

• Simple craters are bowl-shaped with no central uplift.
• Complex craters have a central uplift and are rimmed by terraces, underlain by faults.
• Impact breccia is a common feature in both types of craters.
• Impact melt is also often present.
• Material flow, uplifted material, and faulting are all features associated with complex craters.

Impact Structures in Canada

• Manicougan Crater (Quebec) formed 215.5 million years ago.
• Pingualuit Crater (Quebec) formed approximately 1.4 million years ago.
• Brent Crater (Ontario) formed 435 million years ago.

Sudbury Impact Structure

• 60 x 30 km crater, formed 1.85 billion years ago (Ga).
• Formed from a 10-15 km wide asteroid impact.
• Elliptical shape due to mountain-building collision deforming the original circular crater.
• Ore deposits of nickel, copper, gold, and silver are common in the Sudbury Basin.

Tunguska and Chelyabinsk, Russia

• Tunguska (1908): A 50-200 m asteroid exploded 5-10 km high, releasing 10-15 megatons of energy.
• Flattened 80 million trees. No fatalities.
• Chelyabinsk (2013): A 10 million kg, 17 m diameter meteoroid exploded.
• Explosions blew out windows and shook buildings.
• ~1,500 people were injured due to shattering glass.

Tunguska, Russia

• A large blast flattened trees over a wide area.
• The area of tree-trunk orientation was also significant.
• A wildfire limit was apparent after the explosion.

Tunguska Scale

• The Tunguska event was a significant airburst, not a ground impact.
• Maps and diagrams illustrate this effect.

The End-Cretaceous Impact

• A large impact event occurred at the end of the Cretaceous period.
• This event is associated with the extinction of dinosaurs.

Evidence of Asteroid Impact

• Iridium, a rare element on Earth, is found in enriched layers marking the end of the Cretaceous period globally.
• No dinosaur bones are found above these layers.

End Cretaceous Asteroid Impact

• Thick layers of shocked quartz, spherules, and tsunami deposits are evidence of a major impact.
• These deposits are found in Eastern North America and the Caribbean.

Chicxulub Crater

• A ring of cenotes marks the edge of the buried crater.
• Water flow and dissolution of overlying limestone were influenced by the buried crater.
• The crater is located in the Yucatan Peninsula.

Cretaceous Geography

• A map shows the arrangement of continents during the Cretaceous period.

End-Cretaceous Climate Change

• A graph shows the temperature fluctuations after the impact, including a sudden drop.
• The atmosphere was initially loaded with dust, which caused a drop in temperature.
• Greenhouse warming occurred later due to CO2.

End-Cretaceous Impact: Problems for Life

• A major earthquake of magnitude 11.3 affected the region due to the impact.
• Wildfires raged globally or regionally.
• Acid rain was a result.
• Sunlight was blocked by dust and soot resulting in photosynthesis inhibition.
• Global warming occurred as water vapor and CO2 remained in the atmosphere.

End-Cretaceous Impact: Problems for Life

• Tsunami up to 300 m high followed the impact in shallow seas.
• Steam bubbles of 500 km³ volume caused extensive atmosphere disturbances.
• An asteroid impact in the limestone-rich region contributed additional CO2 into the atmosphere; raising temperatures up to 10 °C.
• Co-occurring Deccan flood basalt eruptions began 250,000 years before the Chicxulub impact and continued for 500,000 years.

Risk Assessment

• The Torino Scale is used to assess potential asteroid impact risks.
• Asteroid impact frequencies are estimated from Moon craters.
• The odds of an impact are relatively low, although the effects of a large impact would be substantial.

Near-Earth Objects

• 90% of Near-Earth Asteroids (NEAs) are not on a collision course with Earth.
• NASA searches for 140 m "city-killers" and has identified more PHAs.

DART Mission

• NASA's DART mission is the Double Asteroid Redirection Test.
• The mission aims to change the path of an asteroid and prove deflection techniques.
• The mission arrived in fall 2022.

Explore the fascinating world of meteorite impacts and their effects on the Earth's surface. This quiz covers the formation of simple and complex craters, notable impact structures in Canada, and the geological features associated with these impacts. Test your knowledge and understanding of these natural phenomena!