Tell me why would it be hard to use volcanic eruptions or earthquakes to mark the start of periods?

Humans impact the physical environment in many ways: overpopulation, pollution, burning fossil fuels, and deforestation. Changes like these have triggered climate change, soil erosion, poor air quality, and undrinkable water.  ecosystems are vital for human welfare and survival, as they provide us with essential products and benefits.

Over 90% of our food comes from terrestrial ecosystems, which also provide energy, building materials, clothes, medicines, fresh and clean water, and clean air. Protecting wildlife and preserving it for future generations also means that the animals we love don't become a distant memory. And we can maintain a healthy and functional ecosystem.