  As a group-theoretic foundation of gravity, it is considered an
affine-Goldstone nonlinear model based upon the nonlinear realization of the
global affine symmetry spontaneously broken at the Planck scale to the Poincare
symmetry. It is shown that below this scale the model justifies and elaborates
an earlier introduced effective field theory of the quartet-metric gravity
incorporating the gravitational dark substances emerging in addition to the
tensor graviton. The prospects for subsequent going beyond the nonlinear model
above the Planck scale are indicated.
