The Earth is not a perfect sphere and doesn't have a solid and complete shape due to various factors:
Rotation: The Earth rotates around its axis, causing it to flatten slightly at the poles and bulge at the equator. This shape is known as an oblate spheroid. The rotation creates a centrifugal force that counteracts the gravitational force, causing the equatorial region to experience a slightly greater outward force and resulting in a broader circumference compared to the polar regions.
Geophysical Features: The Earth's surface is diverse and contains mountains, valleys, oceans, and other geophysical features. These irregularities contribute to the planet's uneven shape. For example, mountain ranges like the Himalayas or the Andes can locally affect the shape of the Earth's surface.
Tectonic Activity: The Earth's lithosphere, which consists of rigid plates that float on the semi-fluid asthenosphere beneath them, is in constant motion. Tectonic activity, including the movement of plates, volcanic eruptions, and earthquakes, can create variations in the shape of the Earth's surface.
Gravitational Variations: The distribution of mass across the Earth is not uniform. Variations in the density of materials in different regions cause slight gravitational anomalies. These gravitational variations can influence the shape of the Earth, leading to deviations from a perfect sphere.
Dynamic Processes: The Earth's atmosphere, oceans, and other dynamic processes also contribute to the planet's shape. Atmospheric pressure, wind patterns, ocean currents, and tidal forces can cause localized bulges or distortions on the Earth's surface.
It's important to note that while the Earth is not a perfect sphere, it is still remarkably close to being one. The deviations from a perfect sphere are relatively small compared to the overall size of the planet. Scientists and geodesists use models and measurements to accurately represent the Earth's shape, taking into account these various factors to create models like the World Geodetic System (WGS84) or the Geodetic Reference System (GRS80) that provide a reference shape for navigation, mapping, and scientific purposes.