### Origins of Prebiotic Organic Molecules How did organic molecules, the building blocks … — ACT

### Origins of Prebiotic Organic Molecules

How did organic molecules, the building blocks of life, first accumulate on early Earth? Two researchers propose different hypotheses.

Researcher 1
Organic molecules on early Earth were synthesized endogenously (locally) at deep-sea hydrothermal vents. The reducing fluids rich in dissolved gases such as hydrogen ( $H_2$ ) and carbon dioxide ( $CO_2$ ) reacted in the presence of iron-sulfide mineral catalysts. These chemical reactions occurred at high temperatures ( $100^\circ\text{C}$ to $350^\circ\text{C}$ ) and high pressures, producing amino acids and other complex organic compounds. Early Earth's atmospheric composition was irrelevant to this process because the synthesis occurred deep within the oceans, isolated from the atmosphere.

Researcher 2
Organic molecules on early Earth were delivered exogenously by carbonaceous meteorites and cosmic dust during the Late Heavy Bombardment. Synthesis of these molecules occurred in interstellar space under extremely low temperatures (near $-260^\circ\text{C}$ ) and low pressures, catalyzed by UV radiation on ice-grain surfaces. Endogenous synthesis at hydrothermal vents was impossible because the high temperatures ( $>100^\circ\text{C}$ ) at these vents would rapidly decompose, rather than build, complex organic molecules like amino acids.

Based on the viewpoints of Researcher 1 and Researcher 2, on which of the following points do the two researchers disagree?

A
Whether complex organic compounds like amino acids were present on early Earth.
B
Whether organic molecule synthesis in interstellar space was catalyzed by iron-sulfide minerals.
Whether the high temperatures of hydrothermal vents allow for the stable synthesis of complex organic molecules.Answer
D
Whether the chemical reactions that produced early organic molecules required the presence of a catalyst.

Answer

Whether the high temperatures of hydrothermal vents allow for the stable synthesis of complex organic molecules.

The correct answer is correct because Researcher 1 argues that organic molecules were synthesized in high-temperature (100°C to 350°C) deep-sea hydrothermal vents, while Researcher 2 asserts that these high temperatures would decompose rather than build organic molecules, making endogenous synthesis at vents impossible.

Step-by-Step Solution

Identify Researcher 1's position on the temperature of synthesis.

Researcher 1 states that synthesis occurred at high temperatures (

100^\circ\text{C}

350^\circ\text{C}

) at deep-sea hydrothermal vents.

To establish the temperature conditions proposed in the first hypothesis.

Identify Researcher 2's position on the temperature of synthesis and hydrothermal vents.

Researcher 2 states that synthesis occurred in interstellar space at near

-260^\circ\text{C}

and that the high temperatures (

>100^\circ\text{C}

) of hydrothermal vents would decompose organic molecules.

To establish the temperature conditions proposed in the second hypothesis and find where they conflict with the first.

Compare the two positions to determine the point of disagreement.

The researchers disagree on whether the high temperatures of hydrothermal vents permit the stable synthesis and survival of organic molecules.

To select the option that represents this disagreement.

Key Concept

Identifying points of disagreement between conflicting scientific viewpoints based on their premises and mechanisms.

Estimated Time:1m 30s

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