Final answer:
Volcanoes and comets were both significant contributors to the development of Earth's atmosphere; volcanoes through gaseous emissions and comets through the delivery of water and organics. Their combined effects were critical in forming the atmospheric and hydrospheric conditions necessary for life.
Step-by-step explanation:
Volcanoes and comets have played instrumental roles in the formation and development of Earth's atmosphere. Early in Earth's history, as it cooled, volcanic activity emerged as a significant force, releasing critical gases such as water vapor, carbon dioxide, and other gases into the primitive atmosphere. This volcanic outgassing helped to create the initial conditions necessary for the planet's atmosphere.
On the other hand, the role of comets in atmospheric evolution is tied to the delivery of water and organic compounds. During the heavy bombardment phase of the early Solar System, Earth and other planets were frequently impacted by comets and asteroids containing ice and other volatile materials. These impact events likely contributed substantially to the Earth's supply of water and complex organic molecules, possibly influencing the development of life.
Therefore, both volcanoes and comets are fundamental to our understanding of how Earth's atmosphere and hydrosphere developed over geological time scales. The consensus among scientists is that a combination of volcanic degassing and comet impacts formed the essential components of our atmosphere and oceans.