Final answer:
The Apollo asteroids are the group that crosses Earth's orbit and may pose a collision risk, different from the main asteroid belt's population. Their unstable orbits can lead to impacts or ejection from the solar system, and they are of interest to various global stakeholders for safety planning.
Step-by-step explanation:
The group of asteroids that crosses the Earth's orbit and could be potentially responsible for future collisions with Earth and mass extinctions is known as the Apollo asteroids. These are a subset of Earth-approaching asteroids whose orbits not only approach Earth's orbit but some actually cross it. The significance of Apollo asteroids lies in their precarious orbits that could change over time due to gravitational interactions, leading to possible impacts with Earth.
A large fraction of asteroids are located in the main asteroid belt between Mars and Jupiter. However, unlike those, the Apollo asteroids, along with other groups like the Amor and Aten asteroids, occasionally come close or intersect Earth's orbit, carrying the risk of a catastrophic collision similar to the one that may have resulted in the extinction of the dinosaurs 65 million years ago.
The orbits of these asteroids are highly influenced by the gravitational forces exerted by the planets, which might lead to either an impact with Earth or their ejection from the inner solar system. Given their potential threat, these celestial bodies are closely monitored by astronomers and pose interest not just for scientific communities, but also for international security and emergency preparedness.