Solar System and Impacts

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A cloud of dust and collapsed inwards by about 5000 million years ago. The collapsing matter produced a , our Sun, mainly from the element . It became hotter and began to glow. Other matter collapsed under gravity, forming large masses which in turn attracted even more matter. This was the start of the formation of the . Also formed during this time were many smaller masses, known as , which are located between Mars and Jupiter. The pull of gravity from can sometimes move asteroids out of their orbits, and they can head towards Earth. Other objects orbit the sun. Some of these have very elliptical orbits and can take hundreds of years for one orbit. These are called , and are often described as 'dirty snowballs' . They are drawn into the solar system by the action of gravity of the outer planets.

Many planets are covered with . These are the result of impacts from objects such as meteorites and asteroids. These impacts can also be seen clearly on the Moon. The evidence of impacts on Earth has been reduced by the erosion of the surface over thousands of years. Plate also is a mechanism which can disguise or eliminate evidence of impacts. The Earth is being constantly by cosmic dust and meteorites. Many of these objects in the atmosphere as they travel at high velocities. The friction with the atmosphere results in very high , and combustion can easily occur in the presence of . One of the most striking exampes of these impacts is Barringer Crater, in . It is 1km in diameter and over 200m deep. In 1991 a massive crater was discovered in . The age of the Chicxulub crater, mainly hidden beneath the , is calculated to be 65 million years. The asteroid was thought to be over 12000 meters in diameter. Evidence of the impact is found in a thin layer of dark material in rocks around the world, containing Iridium. This is known as the K-T boundary.

The time of this impact at Chicxulub coincides with the time when became extinct. In this theory very large quantities of dirt, dust and poisonous fumes were launched into the atmosphere. Without energy from the Sun, the Earth became colder and for plants (food) became impossible. However, other scientists state that many dinosaurs were beginning to die before the asteroid impacted Earth. They also state that other large impacts are not linked with any mass extinction. Other theories of mass extinction include disease, drought, lack of food supplies, and large flows of lava. Evidence of large lava flows can be observed in , where over one third of the land is covered with basalt. However, not all large lava flows and volcanic eruptions around the world are linked to mass extinctions.