Question

1. cite evidence from the article to support the authors claim.

article excerpt 2
water molecules were surely part of the dusty swirl that coalesced into the sun and its planets beginning about nine billion years after the big bang. but earths early history, including epochs with high ambient temperatures and no enveloping atmosphere, implies that surface water would have evaporated and drifted back into space. the water we encounter today, it seems, must have been delivered long after earth formed.
faced with this conundrum, astronomers realized that there are two ready - made sources: comets and asteroids. the solar system gravel strewn among planetary boulders. the primary difference between the two is that comets typically have a greater concentration of ingredients that vaporize when heated, accounting for their iconic gaseous tails. both comets and asteroids can contain ice. and, by colliding with earth, they added the amount of material some scientists suspect, such bodies could easily have delivered oceans worth of water. accordingly, each has been fingered as a suspect in the mystery.
greene, brian. \how did water come to earth.\ smithsonian.com.smithsonian magazine, may 2013.

1. according to the article, where did earths water come from?
2. cite evidence from the article to support the authors claim.
3. after reading both articles, where do you think earths water came from? cite evidence from the articles to support your claim.

Explanation:

1. The article states that water molecules were part of the dusty swirl that formed the Sun and planets, but Earth's early high - temp and no - atmosphere conditions imply surface water evaporated. Comets and asteroids are proposed as sources as they can contain ice and could have delivered water upon collision.
2. According to the article, Earth's water is thought to have come from comets and asteroids. Evidence: "Astronomers realized that there are two ready - made sources: comets and asteroids... Both comets and asteroids can contain ice. And, by colliding with Earth, they added the amount of material some scientists suspect, such bodies could easily have delivered oceans' worth of water."
3. Similar to the answer for 2, the evidence for the claim about comets and asteroids being sources of Earth's water is that they can contain ice and upon collision with Earth could have delivered large amounts of water.
4. Based on the article, a likely source is comets and asteroids. Evidence: They contain ice and could have collided with Earth to deliver water. Also, Earth's early conditions were not conducive to retaining surface water, so an external source like comets and asteroids is proposed.

Answer:

1. Water molecules were in the initial swirl but Earth's early conditions were not good for retaining surface water. Comets and asteroids can contain ice and could have delivered water on collision.
2. Comets and asteroids.
3. Comets and asteroids contain ice and could have delivered water on collision with Earth.
4. Comets and asteroids. Evidence: They contain ice and could have collided with Earth to deliver water, and Earth's early conditions made it hard to retain surface water.