« Sound and apece > > 6.3 Formation of the Moon © describe evidence for the collision theory for the formation of the Moon. Work in groups. Discuss how the Solar System was formed from a cloud of dust land gas in space.6.3 Formation of the Moon Where did the Moon come from? In the early twentieth century, scientists thought that the Moon was formed by splitting away from the Earth, soon after the Earth was formed. Calculations showed that. if this theory was correct, the Moon would still be slowly moving away from Earth. Accurate measurements made ‘more recently have shown that the Moon és still moving away from Earth —at a rate of about 4 em each year. ‘These calculations could not completely confirm the theory that the Moon had formed by splitting away from the Earth \was suggested that the Moon was formed in a different way, collision theory. Collision theory for formation of the Moon ‘The collision theory (also called the giant impact hypothesis) is another theory of how the Moon was formed. There is more evidence that supports the collision theory than any other current theory. ‘The collision theory refers to a collision that happened relatively soon after the formation of the Solar System. A newly formed planet, about the same size as Mars, collided with the nowly formed Earth. ‘Scientists have called the colliding planet Theia. The picture ~ drawn by anartist - shows what the collision between Earth (left) and ‘Theia may have looked like. 2s >6 Sound and space > ‘The collision would have caused rocks and dust to break away from both planets. The theory states that Earth was formed from the two planets joined together. The Moon was formed when the rocks and dust, ‘was pulled together by gravity. These stages are shown in this diagram: “eo oa -e@ ring eocks and ust sock nd ductcome ‘egethetofarm the Moon ‘The Moon is less dense than the Earth. ‘The surface of the Earth does not appear ‘Samples of rock from the Moon show that its | t@ €ver have been molten. A collision that, formed the Moon would have caused the surface of the Earth to melt. The surface ilar to | would have later solidified. surface was once molten ‘The Moon has a small iron core, the Earth, ‘Venus has no meen. Collisions in the early ‘There is evidence outside the Solar System | years of the Solar System would have of similar collisions causing rings of rock and | been common and scientists would have dust ‘expected Venus to have a moon formed in ‘The collision theory fits with the theory of __| the same way hhow the Solar System was formed ‘The composition of rocks on the Moon The composition of racks on the Earth and | would be expected to be more similar to tho Moon aro the same. rocks on Theia than rocks on Earth. In fact, the composition of the Moon is more similar to Earth >6.3 Formation of the Moon Questions 1 The collision theory suggests that an object called Theia collided with Earth, Which of these planets is closest in size to Theia? Write one letter. A. Mars B Earth = C Neptune © Jupiter Which of these statements could explain why the composition of rocks on the Earth and on the Moon is very similar? ‘Write one letter ‘A. ‘The Moon is mostly formed from Theia’s rocks and the Earth only has & small quantity of Theta’s rocks B The Earth is mostly formed from "Theia’s rocks and the Moon only has a small quantity of Theia’s rocks © Rocks from Theia and Earth were completely mixed during the coll ‘The planet Mars has two moons called Phobos and Deimos, Scientists have evidence that Phobos and Deimos are asteroids that were captured by the gravity of Mars, so they remain in orbit ‘around Mars. ‘Suszest how the composition of rocks on Phobos and Deimos ‘would compare with the rocks om the planet Mars if Phobos and Deimos were: 2 originally asteroids b formed by a collision of another object with Mars, Models of the formation of the Solar System show that collisions ‘between planet-sized objects would fave been common soon after the Solar System formed. Suggest why these collisions are no longer common.In this activity, you will do your own research to find evidence. Work in groups of three or four. Use an internet search engine to find out more about the collision theory of the formation of the Moon, Some scientists call it the giant impact hypothesis, 50 you should also search for that. Try to find websites other than general encyclopaedia sites information that you can understand evidence that supports the collision theary evidence that contradicts the collision theory other theories on how the Moon was formed. Produce a report an what you find. Write this in your own words as much as possible Your report can take any form. Include: the websites where each piece of information was obtained which websites you thought were most reliable whether any of the websites were biased why you had to use secondary sources rather than first-hand experience which theory you think is correct and why. | know the collision theory for the formation of the Moon. | know the evidence for the collision theory.