Mysteries Behind the Largest Impact Craters on Earth
written by: Dorothy Bland•edited by: RC Davison•updated: 6/13/2010
Asteroids entering the Earth's atmosphere are nothing new. However, most do not result in wide-spread planetary changes. Here we look at the largest impact craters on Earth, and the effects they had on the planet.
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An object the size of a small city, streaks through the sky on a collision path with Earth. Moving at supersonic speed, it hits the Earth's surface and triggers a massive explosion - activating earthquakes, mega-tsunamis, volcanic eruptions and wildfires. Dust particles rise up in the air, blocking the sunlight and cooling the planet. The effects do not happen in just the area of impact, they are felt all around the globe; creating harsh living conditions for all life left on Earth. Though such an object striking the planet and triggering such catastrophic effects may seem like a plot line from a doomsday movie, such events have occurred...
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Understanding Impact Craters
So what object is capable of causing such destruction? An asteroid from space! When small objects enter the Earth's atmosphere they usually disintegrate, large asteroids and comets however, do not. Instead, these objects end up slamming into the Earth. The instantaneous event releases a shock wave that spreads out from the area of impact. The explosion of energy forces material to fly out in all directions at once, destroying or fragmenting the cosmic projectile and leaving behind a roughly circular shaped depression or hole.
A look around the Solar System shows collisions with cosmic debris is a common event. Take the Moon for instance, the rocky satellite bares the scars from millions of impacts. Though Earth has a stronger gravitational pull than the Moon, impact craters are not as visible due to geologic activity. Causing impact craters to be removed or buried due to erosion, plate tectonics and volcanic activity. According to the Earth Impact Database, less than 200 impact crater sites have been confirmed. Here we look at the largest impact craters on Earth based on diameter.
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4. Manicouagan Crater & Popigai Crater
At 100 km in diameter, the Manicouagan crater is tied with the Popigai crater as the fourth largest impact crater on Earth. The impact crater is the result of a 5 km asteroid, colliding with Earth approximately 215 million years ago. Located in Quebec, Canada, the crater has been somewhat worn away by glaciers and erosion and now measures about 70 km. Despite its age and erosion however, the impact crater has held up well, the hard rock at its impact site gives it more resistance to erosion.
At only 36 million years old, the Popigai crater located in Siberia, Russia is actually the youngest on this list. An asteroid measuring at least 5 km in diameter created the structure; generating a shock that instantly created diamonds in the crater.
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3. Chicxulub Crater
Carved out at the end of the Cretaceous period, the Chicxulub crater in Mexico's Yucatan Peninsula is probably the most studied and well known impact crater on the planet. The crater however, cannot be seen on the surface of the Earth and is mainly located underwater. Measuring 180 km wide and 900-meters deep, the crater was the result of a 10 km wide asteroid or comet striking the planet's surface 65 million years ago. Most scientists support the theory that the impact crater was responsible for forever changing life on Earth. The impact triggered a number of devastating events including worldwide climate changes and geological activity. According to NASA, the impact led to the extinction of over 70 percent of plant and animal life on the planet. The resulting changes would wipe out the dinosaurs and allow mammals to become the dominant species on the planet.
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Just like the other inner planets in the solar system and the Moon, Earth has her share of impact craters to explore. Find out more about the 5 largest impact craters on Earth, which range from Canada to Siberia to Africa, and learn their importance to evolution and extinction.
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2. Sudbury Crater
Canada has several of the largest impact craters on Earth, none larger than the Sudbury crater located in Ontario. Dating around 1.85 billion years old, the impact is believed to have been caused by a comet. Originally boasting a rim diameter of 250 km, erosion and deformation of the crater have left a basin measuring 62 km long and 15 km deep. The impact allowed the basin to fill up with precious minerals from Earth's mantel including nickel, copper and platinum. Today, the basin is an active mining community - one of the biggest and richest in the world.
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1. Vredefort Crater
Measuring 300 km in diameter, the biggest verified impact crater on Earth can be found in South Africa. Called the Vredefort crater, the multiple ring structure is twice the size of the Chicxulub Crater. The impact event occurred over 2 billion years ago, at a time when only elementary single-celled forms of life existed. The amount of energy released during impact caused an unimaginably gigantic explosion – the largest single release of energy in the world. Many scientists speculate that this release of energy triggered major evolutionary changes, increasing the levels of oxygen in the atmosphere and creating an environment that allowed complex forms of life to evolve.
The site has been inhabited by humans since the Stone Age and even had a gold rush. Over time, Vredefort crater has eroded down to around 190 km in diameter. Deemed culturally important and worthy of preservation the site is now a UNESCO World Heritage Site. As the oldest verified impact crater, the site is of particular interest to scientist.
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So, is there a chance that doomsday movies have got it right and a large asteroid will wipe out human life in the next few years? Don’t start preparing for the end of the world just yet. Though objects regularly enter the Earth's atmosphere, large impacts are much rarer today then they were several billion years ago. According to information released by NASA's Asteroid and Comet Impact Hazards, a meteoroid large enough to cause global catastrophe would need to be 2 km in diameter, the equivalent of 1 million megatons of energy. Statistically speaking, objects of this size only strike the Earth about once every one million years.
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A 'Smoking Gun' for Dinosaur Extinction (http://www.jpl.nasa.gov/news/features.cfm?feature=8)