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GED Science: Space and Earth's History Concepts

Importance ★★★☆☆ · 25% (estimate)

Overview

This chapter covers Earth's place in space and how scientists know Earth's age. Questions often give a short table of planet data or describe rock layers.

The Sun is a star, one of billions in the Milky Way galaxy. A star like the Sun becomes a red giant near the end of its life and then a white dwarf; only much more massive stars can become neutron stars or black holes. Earth spins on its axis about once every 24 hours, which causes day and night, and orbits the Sun once a year. The tilt of Earth's axis causes the seasons.

The Moon's gravity is the main cause of tides. In a solar eclipse the Moon is between the Sun and Earth; in a lunar eclipse Earth is in the middle.

Planets farther from the Sun take longer to orbit it. Earth's history is read from rocks. In undisturbed layers of sedimentary rock, the bottom layer is oldest, and fossils show what lived at different times. Radiometric dating uses half-life: each half-life, half of a radioactive element's atoms change, so counting how much is left tells the age of a rock.

Key concepts

  • Day and night

    Caused by Earth spinning on its axis, about once every 24 hours.

    Memory tipSpin = a day; orbit = a year.

  • Seasons

    Caused by the tilt of Earth's axis, not by its distance from the Sun.

    Memory tipTilt toward the Sun = summer.

  • Tides

    Caused mainly by the Moon's gravity pulling on the oceans.

    Memory tipThe Moon is the main cause; the Sun adds a smaller pull.

  • Eclipses

    Solar: Moon between Sun and Earth. Lunar: Earth between Sun and Moon.

    Memory tipSolar = Sun is blocked; lunar = Moon is darkened.

  • Life of a Sun-like star

    Main-sequence star → red giant → white dwarf.

    Memory tipOnly very massive stars become black holes.

  • Half-life

    The time for half of a radioactive element's atoms to change. After 2 half-lives, one-fourth remains.

    Memory tipCount how many times you halve, then multiply by the half-life.

Often tested

  • Earth is closest to the Sun in early January, so distance does not cause seasons.
  • Undisturbed rock layers: oldest at the bottom.
  • Use only the data given; do not add facts the table does not show.

3 sample questions

Verified practice questions from this unit.

Practice questionReviewedEarth and Space Science › Space and Earth's History★★★★☆

Question 1. What causes day and night on Earth?

  1. ① Earth spinning on its axis
  2. ② Earth moving around the Sun
  3. ③ The Moon blocking the Sun each evening
  4. ④ The Sun moving around Earth
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Answer: ① Earth spinning on its axis

Key point: Rotation (spin, about 24 hours) causes day and night

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.
Practice questionReviewedEarth and Space Science › Space and Earth's History★★★☆☆

Question 2. What causes Earth's seasons?

  1. ① The phases of the Moon
  2. ② Changes in Earth's distance from the Sun
  3. ③ The Sun turning on its own axis
  4. ④ The tilt of Earth's axis as Earth orbits the Sun
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Answer: ④ The tilt of Earth's axis as Earth orbits the Sun

Key point: Seasons come from the tilt of Earth's axis

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.
Practice questionReviewedEarth and Space Science › Space and Earth's History★★★☆☆

Question 3. What is the main cause of ocean tides on Earth?

  1. ① Earth's magnetic field
  2. ② Earthquakes on the sea floor
  3. ③ The pull of the Moon's gravity
  4. ④ Wind blowing across the ocean
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Answer: ③ The pull of the Moon's gravity

Key point: Tides are caused mainly by the Moon's gravity

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.
Practice 5 questions from this unit →

AI-written · Verified · Written by AI. Only units that passed a separate AI check (re-reading facts and numbers) are published. Tell us if you find a mistake.