Scientists have detected more than 160 asteroid impact craters on Earth's surface as of July 2014. Most of these were cataloged before 1950, and a few new ones are discovered each year. The largest impact crater is 236 miles across in South Africa due to an impact that happened more than 2 billion years ago. Asteroids more than 6 miles across create layers of pulverized rock on the surface.Continue Reading
Impact craters on Earth come in two different types. Smaller craters are less than 2 miles in diameter with a bowl-shaped depression and some rock fill in the middle. Larger craters are more than 2 miles across with a central peak, melted rocks and a slumped rim.
The Vredefort Crater in South Africa is a UNESCO World Heritage Site. The impact crater is the largest and one of the oldest on Earth. The Sudbury Basin in Ontario, Canada, is 1.8 billion years old and 81 miles in diameter. This part of Canada is the second-largest impact crater in the world.
Large asteroids more than 6 miles wide that strike the Earth create plumes of pulverized rock, called spherules, that are ejected into outer space due to the violence of the impact. Spherule layers settle back to the surface, and these layers are detected by scientists. Spherule layers are dated by surrounding layers of rock to give geologists an idea of when large asteroid impacts occurred.Learn more about Geology
Sedimentary rocks are formed by the deposition of mud, clay, sand and other small particles on the surface of the Earth. Sedimentation can occur in many different environments, including lakes, rivers, deserts and oceans. The sediment is deposited in layers that are compressed over time and turned into solid rock.Full Answer >
The theory of plate tectonics states that the Earth's surface, the upper mantle and crust, was once made up of enormous rock plates that broke into smaller pieces approximately 300 million years ago. These smaller, broken plates form a more fluid rock surface in the mantle. Over time, the plates move and morph into natural land boundaries. This explains natural land phenomena, such as earthquakes and tsunamis.Full Answer >
The depth of the bedrock layer varies significantly throughout the Earth; in some areas, the bedrock layer is exposed, while in others it is hundreds of meters below the surface. Scientists believe that bedrock extends to the base of the planet's crust.Full Answer >
Magma rises to the Earth's surface due to a combination of differences in density with other rocks in the crust and pressure. The differences in density cause it to move upward until its density is the same as the other rocks in the crust. It then builds pressure, causing it to rise to the surface.Full Answer >