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.Know More
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
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 >
Crustal plates are large sections of the outer layer of the Earth's surface that move along convection currents in the mantle. There are 10 major plates on the surface, and the tectonic forces behind their movement create earthquakes, volcanoes and tidal waves.Full Answer >
Basalt is primarily formed by the extrusion of lava flows onto the surface of the earth during a volcanic eruption. The intrusion of a narrow sill or igneous dike below the crust also results in the formation of basalt.Full Answer >
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 >