Final answer:
Without the atmosphere and the greenhouse effect it provides, Earth would experience a significant decrease in surface temperature, as the heat from the Sun would be radiated back into space.
Step-by-step explanation:
If the atmosphere did not exist, the interaction that would most likely happen on Earth includes a significant decrease in surface temperature. This is due to the absence of the greenhouse effect, which is critical in retaining heat from the Sun and warming the planet's surface. Greenhouse gases, such as carbon dioxide and water vapor, trap some of the infrared radiation that escapes from Earth's surface, maintaining temperatures suitable for life. Without them, the Sun's energy would be radiated back into space, and the Earth's average temperature would drop considerably, becoming much colder than it currently is.