social studies vocab

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Across
  1. 3. Instruments that detect and record vibrations from earthquakes, used to study Earth's interior
  2. 4. A Mars-sized body thought to have collided with Earth, forming the Moon
  3. 6. A form of an element with the same number of protons but a different number of neutrons
  4. 9. The gradual growth of objects in space as particles stick together due to gravity and collide, forming larger bodies like planets
  5. 11. The thick, semi-solid layer between Earth's core and crust, made of lighter rocks than the core and heavier rocks than the crust, such as basalts, that are mixed with gas and water
  6. 12. The thin, outermost solid layer of planet Earth, formed of the lightest rocks, mainly granite
Down
  1. 1. The process by which unstable atoms release energy and particles over time
  2. 2. The process by which a planet's layers separate based on density
  3. 5. Planets that orbit stars outside our solar system
  4. 7. The longest unit of geologic time, made up of multiple eras
  5. 8. In astronomy, this refers to all elements heavier than helium, important for forming planets and stars
  6. 10. The central, densest layer of planet Earth, made mainly of iron and nickel and responsible for generating the planet's magnetic field