GED Science Space and Earth's History Summary

Earth rotates (spins) on its axis about once every 24 hours. The side facing the Sun has day, and the side facing away has night.

Wrong choices

• Earth moving around the Sun: Earth's trip around the Sun takes one year. That gives us years, not days.
• The Moon blocking the Sun each evening: The Moon blocks the Sun only during a solar eclipse, which is rare.
• The Sun moving around Earth: The Sun does not move around Earth. It only seems to cross the sky because Earth spins.

Earth's axis is tilted. As Earth orbits the Sun, first one hemisphere and then the other leans toward the Sun. The hemisphere tilted toward the Sun gets more direct sunlight and longer days, so it has summer.

Wrong choices

• The phases of the Moon: Moon phases repeat about every month and do not cause seasons.
• Changes in Earth's distance from the Sun: Earth's distance from the Sun changes only a little. Earth is actually closest to the Sun in early January, during winter in the Northern Hemisphere.
• The Sun turning on its own axis: The Sun's spin does not change how much sunlight each part of Earth gets.

The Moon's gravity pulls on Earth's oceans, making the water bulge. As Earth spins, coasts pass through these bulges, giving high and low tides. The Sun's gravity also affects tides, but less than the Moon's.

Wrong choices

• Earth's magnetic field: Earth's magnetic field does not move ocean water.
• Earthquakes on the sea floor: Earthquakes can cause tsunamis, not the regular tides.
• Wind blowing across the ocean: Wind makes waves, but it does not cause the regular daily rise and fall of tides.

In a solar eclipse, the Moon moves directly between the Sun and Earth and blocks the Sun's light for some places on Earth. In a lunar eclipse, Earth is in the middle and its shadow falls on the Moon.

Wrong choices

• When the Moon moves behind the Sun: If the Moon were behind the Sun, it could not block the Sun's light from Earth.
• When the Sun passes between Earth and the Moon: The Sun cannot move between Earth and the Moon.
• When Earth passes between the Sun and the Moon: When Earth is between the Sun and the Moon, Earth's shadow falls on the Moon. That is a lunar eclipse.

The Sun is a star: a huge ball of hot gas that makes energy by nuclear fusion in its core. It is one of billions of stars in the Milky Way galaxy.

Wrong choices

• A comet: A comet is a small icy object that orbits the Sun.
• A galaxy: A galaxy is a huge group of billions of stars. The Sun is one star in the Milky Way galaxy.
• A planet: Planets orbit stars and do not make their own light. The Sun makes light.

A star like the Sun swells into a red giant near the end of its life, then sheds its outer layers. The hot core that remains is a white dwarf. Only much more massive stars explode and can leave a neutron star or black hole.

Wrong choices

• A new planet: Stars do not turn into planets.
• A comet: Comets are small icy objects, not the remains of stars.
• A black hole: Black holes form only from stars much more massive than the Sun.

Sediment settles in layers, with new layers on top of older ones. In undisturbed rock, the bottom layer formed first and is the oldest. Fossils in lower layers are usually older than fossils in higher layers.

Wrong choices

• All layers are the same age: Layers form one on top of another over time, so they are not the same age.
• The middle layer: The middle layer is younger than the layers below it.
• The top layer: The top layer was laid down last, so it is the youngest.

1. 800 → 400 after one half-life.
2. 400 → 200 after two half-lives.
3. Age = 2 × 1.3 = 2.6 billion years.

Check: 800 ÷ 2 ÷ 2 = 200.

Wrong choices

• 0.65 billion years: 0.65 billion years is less than one half-life, so more than 400 atoms would remain.
• 3.9 billion years: After 3.9 billion years (three half-lives), only 100 atoms would remain.
• 1.3 billion years: After 1.3 billion years (one half-life), 400 atoms would remain, not 200.

As the distance from the Sun increases (0.4, 1.0, 1.5, 5.2 AU), the orbit time also increases (88, 365, 687, 4,333 days). So farther planets take longer to go around the Sun.

Wrong choices

• Larger planets are always closer to the Sun.: The table gives no information about the size of each planet.
• Planets farther from the Sun take less time to orbit it.: The data show the opposite: orbit time goes up as distance goes up.
• All planets take one Earth year to orbit the Sun.: Only Earth takes 365 days. The others take more or less time.