ICAS Science Earth and Space — Questions and Answers
Question 1: Why does Australia experience summer in December while the Northern Hemisphere has winter?
- Earth is closer to the Sun in December
- Earth's axis is tilted, so the Southern Hemisphere leans toward the Sun in December (Correct answer)
- The Sun gives off more heat in December
- The Moon blocks sunlight from the Northern Hemisphere
Correct answer: Earth's axis is tilted, so the Southern Hemisphere leans toward the Sun in December
Seasons are caused by Earth's 23.5° axial tilt, not its distance from the Sun.
Earth's axis is tilted about 23.5 degrees. In December the Southern Hemisphere is tilted toward the Sun, receiving more direct sunlight and longer days, so it is summer there. Earth is actually slightly closer to the Sun in early January, but that has almost no effect compared with the tilt.
Question 2: Which layer of Earth is liquid and responsible for generating the planet's magnetic field?
- Crust
- Mantle
- Outer core (Correct answer)
- Inner core
Correct answer: Outer core
The outer core is liquid iron and nickel; its movement creates Earth's magnetic field.
Earth has four main layers: crust, mantle, outer core and inner core. The outer core is made of molten iron and nickel, and the flow of this liquid metal produces Earth's magnetic field. The inner core is also iron and nickel but is solid because the pressure there is so enormous.
Question 3: A student notices that the Moon looks like a thin curve on Monday and a full circle about two weeks later. What causes these changes in the Moon's appearance?
- Earth's shadow falling on the Moon
- Clouds covering parts of the Moon
- The changing amount of the Moon's sunlit side we can see from Earth (Correct answer)
- The Moon changing shape as it orbits
Correct answer: The changing amount of the Moon's sunlit side we can see from Earth
Moon phases occur because we see different amounts of the Moon's lit half as it orbits Earth.
The Sun always lights up half of the Moon. As the Moon orbits Earth over about 29.5 days, we see different portions of that lit half, which creates the phases from new moon to full moon and back. Earth's shadow only affects the Moon during a lunar eclipse, not during normal phases.
Question 4: Which type of rock forms when layers of sediment are compressed over millions of years?
- Igneous
- Sedimentary (Correct answer)
- Metamorphic
- Volcanic
Correct answer: Sedimentary
Sedimentary rock such as sandstone forms from compacted and cemented layers of sediment.
Sedimentary rocks form when particles of sand, mud or shells settle in layers, usually under water, and are squeezed and cemented together over long periods. Examples include sandstone, limestone and shale. Igneous rock forms from cooled magma or lava, while metamorphic rock forms when existing rock is changed by heat and pressure.
Question 5: In the water cycle, which process moves water from the surface of oceans and lakes into the atmosphere?
- Condensation
- Precipitation
- Evaporation (Correct answer)
- Infiltration
Correct answer: Evaporation
Evaporation turns liquid water into water vapour that rises into the air.
The Sun heats water on the surface of oceans, lakes and rivers, causing it to evaporate and rise as water vapour. Higher up it cools and condenses into clouds, and eventually falls as precipitation. Infiltration is when water soaks into the ground.
Question 6: Which of these statements about the planets in our Solar System is correct?
- Venus is the largest planet
- Mars is the closest planet to the Sun
- Jupiter has the shortest year
- Mercury has the shortest year (Correct answer)
Correct answer: Mercury has the shortest year
Mercury is closest to the Sun and orbits it in just 88 Earth days.
A planet's year is the time it takes to orbit the Sun once. Mercury, the closest planet, completes an orbit in about 88 Earth days, the shortest of any planet. Jupiter is the largest planet and takes almost 12 Earth years to orbit, while Venus is similar in size to Earth.
ICAS Science Earth and Space
Why does Australia experience summer in December while the Northern Hemisphere has winter?