Grade 6 Science: Earth and Space

Step 1: Earth’s axis is tilted about 23.5 degrees, and it stays pointed the same way in space all year as Earth travels around the Sun.

Step 2: In June, the Northern Hemisphere leans toward the Sun. Sunlight hits it more directly and the days are longer, so it heats up: summer.

Step 3: Six months later, Earth is on the other side of the Sun. The Northern Hemisphere now leans away, the sunlight is slanted and the days are short: winter.

Step 4: In March and September, neither hemisphere leans toward the Sun, so day and night are about equal everywhere.

Step 1: The Moon’s gravity pulls the ocean into a bulge facing the Moon, and a second bulge forms on the opposite side of Earth.

Step 2: As Earth spins, a beach passes through both bulges each day, so most beaches get two high tides and two low tides, about 12 hours and 25 minutes apart. That is the daily tide cycle.

Step 3: The Sun’s gravity pulls on the oceans too. When the Sun, Earth and Moon line up, at new moon and full moon, the pulls add together: spring tides, with the highest high tides and the lowest low tides.

Step 4: When the Moon is at a right angle to the Sun, at first and third quarter moon, the pulls partly cancel: neap tides, with the smallest difference between high and low tide.

Step 1: Water evaporates from the ocean, part of the hydrosphere, into the air.

Step 2: In the atmosphere, the water vapor cools into clouds and falls as rain.

Step 3: The rain soaks into the soil of the geosphere and wears away rock over time.

Step 4: A tree, part of the biosphere, pulls the water up through its roots and releases some back into the air.

Step 1: The crust: solid rock, only about 5 to 70 kilometers thick. Thinnest under the oceans, thickest under mountains.

Step 2: The mantle: about 2,900 kilometers of very hot rock. It is mostly solid, but it flows very slowly, like thick putty.

Step 3: The outer core: liquid iron and nickel. As it moves, it makes Earth’s magnetic field.

Step 4: The inner core: a ball of solid iron and nickel, about as hot as the surface of the Sun. The huge pressure keeps it solid.

Step 1: Granite is an igneous rock: it formed when magma cooled and hardened deep underground.

Step 2: Rain, ice and wind slowly break the granite into sand: weathering. A river carries the sand away and drops it in layers: erosion and deposition.

Step 3: Over time the sand layers are pressed together and cemented into sandstone, a sedimentary rock.

Step 4: Buried deep, heat and pressure change the sandstone, without melting it, into quartzite, a metamorphic rock. If it ever melts into magma and cools, it becomes igneous rock again.

Step 1: Without electricity, families often cook and light their homes by burning wood or kerosene indoors. That is energy poverty, and the smoke causes air pollution that harms their lungs.

Step 2: A small set of solar panels can give the village clean light and power, cutting the indoor smoke.

Step 3: Protecting the village’s soil and water helps farmers grow enough healthy food, which fights malnutrition.

Step 4: Keeping waste and fertilizer out of the river keeps the drinking water safe, which reduces water pollution.

Step 1: Conservation: turn off the lights in empty classrooms and fix dripping faucets.

Step 2: Efficiency: replace old light bulbs with LED bulbs, which give the same light with at least 75 percent less electricity.

Step 3: Technology: put solar panels on the roof to make electricity from sunlight.

Step 4: The same tools work for air and soil: driving less (conservation) and filters on factory smokestacks (technology) clean the air, and planting cover crops keeps farm soil from washing away.