In relativity the time and space coordinates are intertwined and treated on a more or less equivalent basis. Are time and space fundamentally of the same nature, or is there some essential difference between them that is preserved even in relativity?

According to classical physics (Newtonian Mechanics), the time co-ordinate is unaffected by a transformation from one inertial system to another. The time co-ordinate tʹ of one inertial system does not depend on the space co-ordinate x, y, z of another inertial system, the transformation equation for time being tʹ = t. In relativistic physics, however, space and time are interdependent. The time co-ordinate of one inertial system depends on both the time and the space co-ordinate of another inertial system.
According to Minkowski, the external world is not formed of ordinary three dimensional spaces known as Euclidean space; but it is four dimensional space time continuums known as Minkowski space, where the time or more conveniently ict (Where i is the imaginary number) may be regarded to be fourth dimension. Thus an event in Minkowski space can be represented by four co-ordinates (x1, x2, x3, x4) out of which the first three are space co-ordinates. This four dimensional Minkowski space can more conveniently be represented by (3+1) dimensional space time continuum. So space and time are not independent co-ordinates, but that the description of an event must include its co-ordinates in both space and time. For this reason, special relativity usually is formulated in terms of combined space-time coordinates x, y, z, t. Therefore space and time are treated as equivalent coordinates in special relativity.