What Makes Earth Habitable

Why is Earth's mass important for life?

• If Earth had more or less mass, it would not have plate tectonics and would be entirely covered by water.

• If Earth had more or less mass, the atmosphere would be very different, with either too much ammonia and methane or too little oxygen and water.

• If Earth's mass were significantly different, we would be bombarded by cosmic rays that would strip away our atmosphere.

• If Earth's mass were greater, we would be bombarded by meteorites, and if it were smaller, we would not be able to hold the moon in orbit.

Why is it important that we have a rigid lithosphere overlying a weak asthenosphere?

• If we did not have the rigid lithosphere and weak asthenosphere, the earth would not have plate tectonics and would be covered entirely by water.

• If we did not have the rigid lithosphere and weak asthenosphere, the atmosphere would be very different with either too much ammonia and methane or too little oxygen and water.

• If we did not have the rigid lithosphere and weak asthenosphere, we would be bombarded by cosmic rays that would strip away our atmosphere.

• If we did not have the rigid lithosphere and weak asthenosphere, we would be bombarded by meteorites and we would not be able to hold the moon in orbit.

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Why is the molten metallic outer core and the magnetic field important to life on Earth?

• If we did not have the molten core and the magnetic field, the earth would not have plate tectonics and would be covered entirely by water.

• If we did not have the molten core and the magnetic field, the atmosphere would be very different with either too much ammonia and methane or too little oxygen and water.

• If we did not have the molten core and the magnetic field, we would be bombarded by cosmic rays that would strip away our atmosphere.

• If we did not have the molten core and the magnetic field, we would be bombarded by meteorites and we would not be able to hold the moon in orbit.

What would have happened to Earth if it were 10% closer to the sun?

• The planet would be too hot and most water would evaporate.

• Our atmosphere would consist mainly of nitrogen.

• Liquid water and the water cycle would not exist.

• Our sun would have burned out after a few hundred million years so life would not evolve.

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What would have happened if Earth were located 10% further out from the Sun?

• Our atmosphere would consist mainly of carbon dioxide.

• Our atmosphere would consist mainly of nitrogen.

• Our oceans would all be frozen.

• Our Sun would have burned out after a few hundred million years so life would not evolve.

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NGSS.HS-ESS2-4

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What would have happened to Earth if the Sun had been significantly larger than it is?

• Our atmosphere would consist mainly of carbon dioxide.

• Our atmosphere would consist mainly of nitrogen.

• Liquid water and the water cycle would not exist.

• Our Sun would have burned out after a few hundred million years so life would not evolve.

The Goldilocks scenario suggests that ________.

• we are very fortunate that the meteorites that have bombarded Earth over time were not too large or too small

• we are very fortunate to be in the right place in the universe and to have had the right condition to develop and sustain life

• we are very fortunate that dinosaurs were destroyed but left us an inhabitable planet

• we are very fortunate to be in a solar system where life can develop and be sustained

The region around a star in which a planet with sufficient atmospheric pressure could maintain liquid water on its surface and thus might be hospitable to Earth-like life.

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Vocabulary

A planet that orbits a star other than the Sun.

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Vocabulary

Explain why Earth is just the right size:

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Answer explanation

A smaller Earth would not have the gravity to hold on to its atmosphere. A larger Earth would have greater gravity which would have retained its thick, hostile atmosphere of mostly ammonia and methane.