7 EARTH SCIENCE W H A T I S E A R T H S C I E N C E The Earth’s Hemispheres We call the top half of the Earth the Northern Hemisphere and the bottom half the Southern Hemisphere The equator is an imaginary line around the middle of Earth’s surface separating the Northern Hemisphere from the Southern Hemisphere At the top of the Northern Hemisphere is the North Pole The South Pole is at the bottom of the planet in the Southern Hemisphere The closer you live to the equator the warmer your climate And the further away from the equator you live the colder your climate is Another imaginary line runs through the center of the Earth from the North Pole to the South Pole We call this line Earth’s axis The axis tilts at 23 45 degrees Earth rotates around the axis The tilt of Earth’s axis is why our seasons change The seasons in the Southern Hemisphere are opposite of the seasons in the Northern Hemisphere If it is winter in the Northern Hemisphere it is summer in the Southern Hemisphere NORTHERN HEMISPHERE SOUTHERN HEMISPHERE EQUATOR In this illustration the sun’s rays shine more directly on the Southern Hemisphere causing those below the equator to experience summer Equator EARTH SUN
8 W H A T I S E A R T H S C I E N C E EARTH SCIENCE The Origin of Our Planet Scientists believe the Earth was created over 4 5 billion years ago It came from a cloud of dust and gas swirling in space Some of the dust and gas formed the sun The rest became planets in the solar system equator i-KWAY-tur an imaginary line around the middle of the Earth pole pohl one of the two points that are farthest away from the equator the North Pole or the South Pole sphere sfihr a solid shape like a basketball or globe Did you know Earth really isn’t a perfect sphere Earth bulges slightly at the equator making the Earth a geoid Earth rotates spins faster at the equator than at the poles because the poles are closer to Earth’s axis This is what causes the bulge The Sun is the star closest to Earth Months approximate range Northern Hemisphere Season Southern Hemisphere Season December January FebruaryWinter Summer March April MaySpring Fall June July AugustSummerWinter September October NovemberFallSpring What Season Is It
9 EARTH SCIENCE W H A T I S E A R T H S C I E N C E The young Earth looked very different than it does today Intense heat inside the growing planet caused molten or liquid rock to form The hot surface slowly cooled over millions of years Water vapor and other gases made the atmosphere Clouds covered the planet Rain helped cool the hot surface Cooling rocks slowly began to soak up the falling rain When the ground could not hold any more water oceans formed The land above the level of the ocean formed continents and the continents have been moving and changing ever since Sometimes the continents moved together forming a supercontinent before separating again Pangaea was the last supercontinent When Pangaea separated the continents moved into their current formation The solar system is composed of eight planets circling the sun The asteroid belt can be seen between the orbits of Mars and Jupiter Pluto once called the ninth planet is now considered a dwarf planet Earth Sun The supercontinent Pangaea existed 250 million years ago Venus Mercury Mars Jupiter Saturn Uranus Neptune Pluto
The continents weren’t the only thing changing The clouds became thinner and sunlight could shine through Heat and other forces inside the planet continued changing the EARTH SCIENCE surface Ice ages and many living organisms came and went Over billions of years the Earth became the way it is today GEOLOGIC TIMELINE Cenozoic Era 65 million years ago to present time Phanerozoic Eon 543 million years ago to present time Mesozoic Era 248 to 65 million years ago Paleozoic Era 540 to 548 million years ago Quaternary 1 8 million years ago to today Tertiary 65 to 1 8 million years ago Cretaceous 144 to 65 million years ago Jurassic 206 to 144 million years ago Triassic 248 to 206 million years ago Permian 280 to 248 million years ago Devonian 408 to 360 million years ago Cambrian 540 to 500 million years ago Precambrian Time 4 6 billion years ago to 543 million years ago Proterozoic Eon 2 5 billion years ago to 540 million years ago Archeozic Eon 3 9 billion years ago to 2 5 billion years ago Hadean Eon 4 6 billion years ago to 3 9 billion years ago The Earth Today From outer space the Earth looks very blue That is because water covers most of the planet Nearly three quarters of the Earth’s surface is oceans seas lakes rivers and other bodies of water The seven continents cover the rest of the planet North America ATLANTIC OCEAN South America PACIFIC OCEAN ARCTIC OCEAN Europe Asia Africa INDIAN OCEAN PACIFIC OCEAN Australia The Earth’s seven continents and six oceans SOUTHERN OCEAN Antarctica E C N E I C S H T R A E S I T A H W 10
