It's impossible to say there are only three exact things that affect Earth. Our planet is a complex system influenced by countless factors. However, we can highlight three broad categories that encompass many individual elements:

1. Internal Processes: These are forces originating from within Earth itself, like:

* Plate tectonics: The movement of Earth's tectonic plates causes earthquakes, volcanic eruptions, and mountain formation.

* Earth's core: The molten iron core generates Earth's magnetic field, protecting us from harmful solar radiation.

* Internal heat: Residual heat from Earth's formation and radioactive decay drives geological processes.

2. External Processes: These are influences from outside Earth, including:

* Solar radiation: The sun provides energy for life and drives Earth's climate system.

* Gravitational interactions: The gravitational pull of the sun and moon cause tides and affect Earth's orbit.

* Cosmic radiation: High-energy particles from space can impact Earth's atmosphere and life.

3. Human Activity: Our actions have a growing impact on the planet:

* Climate change: Greenhouse gas emissions are altering Earth's climate, causing rising temperatures, sea levels, and extreme weather events.

* Pollution: Air, water, and soil pollution threaten ecosystems and human health.

* Resource depletion: Overuse of natural resources can lead to scarcity and environmental degradation.

These three categories are just a starting point for understanding the diverse factors that influence Earth. Each category encompasses numerous individual elements, and their interactions create a constantly changing and interconnected system.