Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences. Earth's oceans formed (a) during the late stages of accretion as water ice collected on the surface; (b) from water vapor outgassed by volcanoes; (c) when Earth underwent differentiation.

Short answer

The best answer is (b), as oceans mainly formed from volcanic outgassing.

Step-by-step solution

Understanding the Question

The question asks us to determine when the Earth's oceans were formed, and provides three different choices, each referring to a possible process or stage of Earth's formation and development.

Analyzing Option A

Option (a) suggests that oceans formed during the late stages of accretion as water ice collected on the surface. During accretion, Earth was still forming from debris and particles, and water ice could indeed have collected on the surface after the planet cooled down enough.

Analyzing Option B

Option (b) claims that Earth's oceans formed from water vapor outgassed by volcanoes. This means water vapor released by volcanic activity condensed to form liquid water as the Earth cooled, which is a significant and widely accepted theory explaining ocean formation.

Analyzing Option C

Option (c) states that oceans formed when Earth underwent differentiation. Differentiation is the process by which Earth separated into layers based on density but does not specifically refer to ocean formation, making it less likely to be correct.

Selecting the Best Answer

Comparing the explanations, option (b) aligns well with the scientific consensus that volcanic outgassing significantly contributed to ocean formation, making it the most appropriate choice.

Key concepts

Accretion Phase

The accretion phase was one of the earliest stages in Earth's formation. During this phase, small particles collided and stuck together, gradually forming larger planetary bodies. This process took place over millions of years. The Earth at this time was a hot, molten mass undergoing intense bombardment from space debris. As the collisions decreased and the Earth started to cool, water ice could have been delivered to Earth by icy bodies such as comets and asteroids. These impacts would have provided the raw ingredients necessary for water to eventually accumulate on the Earth's surface.
This phase is crucial because it set the stage for Earth's initial water supply, though the water might not have directly formed oceans yet. Instead, the materials collected during the accretion phase provided a foundation that later processes would build upon.
- The accretion phase involved the gathering of particles to form planets. - It ended with the Earth as a molten body that slowly cooled, allowing for water solidification. - Icy bodies from space contributed to Earth's water inventory during this phase.

Volcanic Outgassing

Volcanic outgassing is a key process that significantly contributed to the formation of Earth's oceans. This process involves the release of gases, including water vapor, from the Earth's interior through volcanic eruptions. As the young Earth continued to cool, the water vapor released into the atmosphere began to condense into liquid water. Over time, this accumulated into what became the Earth's oceans.

Volcanoes were much more active in the Earth's early history than they are now, continuously expelling immense quantities of gases and water vapor. This volcanic activity led to a thick atmosphere rich in water vapor. The cooling of the Earth then allowed this water to condense and fall as rain, eventually collecting in low-lying areas and further forming the oceans.

• Volcanic outgassing was essential in providing water vapor that eventually formed oceans.
• Early volcanic activity was extensive, contributing to a dense, water-rich atmosphere.
• As Earth cooled, the atmosphere's water vapor condensed, creating early oceans.

Planetary Differentiation

Planetary differentiation is an important process in the young Earth's development, though not directly responsible for ocean formation. During differentiation, Earth separated into layers based on material density. The densest materials, such as iron and nickel, sank to form the core, while lighter materials formed the crust and mantle.

This process is crucial for understanding the internal structure of the Earth. Differentiation helped create the conditions for volcanic activity by generating heat within the Earth's interior. This internal heat led to melting and movement within the mantle, driving the volcanic outgassing that contributed to ocean formation. However, differentiation itself did not produce the water necessary for oceans; rather, it facilitated processes, like volcanic activity, that did.

• Differentiation refers to the layering of Earth by density.
• It established inner heat sources crucial for volcanic activity.
• While not directly forming oceans, it supported volcanic outgassing, aiding in ocean creation.