The flattened shape of the Earth when seen from space is primarily due to its rotation on its axis, a phenomenon known as oblateness or equatorial bulge. The Earth is not a perfect sphere; it is an oblate spheroid, meaning it is slightly flattened at the poles and bulges at the equator. This shape is a result of the centrifugal force generated by the rotation of the planet.
As the Earth spins on its axis, the centrifugal force causes the material near the equator to be pushed outward, leading to a bulging effect. This bulge at the equator and flattening at the poles give the Earth its oblate shape. The difference between the polar and equatorial diameters is approximately 42.8 kilometers (26.6 miles).
It's worth noting that other factors, such as the distribution of land and water, tectonic activities, and the varying density of Earth's interior, can also contribute to slight irregularities in the planet's shape. However, the primary cause of Earth's flattened shape when viewed from space is its rotation on its axis.