Question

a student reads a list of several measurements.
which measurements are used as evidence of the age of the universe?

1. the amount of dust given off by exploding stars
2. the rate at which galaxies are moving away from earth
3. the rate at which the light emitted by a star switches between red and blue wavelengths
4. the amount of hydrogen present in stars

options:

• 1 and 2
• 2 and 3
• 1, 2, and 3
• 1, 2, and 4

Explanation:

To determine evidence for the universe's age:

• 2 (galaxy recession rate, Hubble's law) and 3 (stellar light shift, stellar evolution) relate to cosmic time. 1 (dust from exploding stars) and 4 (stellar hydrogen) are less direct. Wait, correction: Actually, 2 (galaxy redshift/recession, Hubble’s law to estimate expansion age), 3 (stellar light color shift relates to stellar age, but more: 4 (stellar hydrogen, as stars fuse H, less H over time in older stars) and 2 (galaxy motion) plus maybe 3? Wait, the correct logic: The age of the universe is estimated using Hubble’s law (galaxy recession rate, 2), stellar evolution (light shift, 3) and stellar hydrogen (4, as primordial H is abundant, older stars have less H). Wait, the options: Let's re - evaluate. The standard evidence: Hubble’s constant (galaxy recession rate, 2), stellar evolution (light color shift, 3), and stellar hydrogen (4, as H is the primary fuel, older stars have less H). Also, dust from exploding stars (1) is less relevant. Wait, the options given: The choices are 1 and 2; 2 and 3; 1,2,3; 1,2,4. Wait, no, the options in the image: The options are "1 and 2", "2 and 3", "1,2, and 3", "1,2, and 4". Wait, maybe I misread. Let's re - analyze:
• 2: Galaxy recession rate (Hubble’s law) is key for cosmic expansion age.
• 3: Stellar light shift (e.g., color change with age, or maybe redshift? No, stellar light shift here might refer to stellar evolution, where a star’s light changes as it ages, helping date stars, which helps date the universe.
• 4: Stellar hydrogen: Primordial H is abundant; older stars have less H (fusion consumes H), so H content in stars relates to cosmic age.
• 1: Dust from exploding stars: Supernovae dust, but not a primary age indicator.

Wait, maybe the correct answer is "1,2, and 4"? No, maybe the intended answer is "1,2, and 3"? Wait, no, let's check standard cosmology. The main evidence: Hubble’s law (2), stellar evolution (3, light shift with age), and stellar H (4, as H is the first element, older stars have less H). Also, dust from supernovae (1) – supernovae occur in stellar life cycles, so maybe 1 is also relevant? Wait, the options: The last option is "1,2, and 4". Maybe that's the answer. Wait, perhaps the question’s context considers:

• 1: Dust from exploding stars (supernovae) – supernovae are part of stellar evolution, which is tied to cosmic time.
• 2: Galaxy recession (Hubble’s law).
• 4: Stellar hydrogen (H is the primary fuel, older stars have less H).

So the answer is "1,2, and 4" (the last option).

Answer:

1,2, and 4 (the option "1,2, and 4" as per the multiple - choice options in the problem)