def spreadingRate(Q, beta):
    """
    Calculates the spreading rate on the planet.

    Inputs:
        Q    - pore space heat flow relative to modern Earth [dimensionless]
        beta - scaling parameter [dimensionless]

    Returns:
        r_sr - the spreading rate relative to the modern Earth [dimensionless]
    """

    r_sr = Q**beta

    return r_sr