American researchers have a new theory about how an object struck the Earth and caused the dinosaurs to die off. Scientists mostly agree on where the impact happened about 65 million years ago. They say a huge object struck an area off the coast of what is now Mexico. Astronomers have said the most likely cause of the strike was either an asteroid or a comet. In recent years, researchers have presented evidence that the impact was caused by an asteroid. The theory suggests the asteroid came from an area between the orbits of Mars and Jupiter. But a study by two astronomers from Harvard University presents a new theory, that the crash was caused by a comet. The researchers say the comet came from an area containing icy debris on the edge of the solar system. The area is known as the Oort cloud. Their theory states that the comet was pulled into the solar system by Jupiter’s gravity. The comet then came very close to the sun, whose tidal force caused it to break up into pieces. The researchers believe one of the pieces crashed into the place that scientists have identified in Mexico.