The phenomenon that causes the seasonal changes experienced on Earth is primarily due to the tilt of the Earth's axis and its orbit around the Sun. The Earth's axis is tilted at an angle of approximately 23.5 degrees, leading to variations in sunlight distribution throughout the year. As the Earth orbits the Sun, different regions experience varying intensities and durations of sunlight, resulting in the four distinct seasons: spring, summer, autumn, and winter. This axial tilt is also responsible for significant changes in temperature, weather patterns, and ecological processes that affect both flora and fauna across different regions.