  It has recently been suggested that a gravitational transition of the
effective Newton's constant $G_{\rm eff}$ by about 10%, taking place 50-150
Myrs ago, can lead to the resolution of both the Hubble crisis and the growth
tension of the standard $\Lambda$CDM model. Hints for such an abrupt transition
with weaker gravity at times before the transition, have recently been
identified in Tully Fisher galactic mass-velocity data and also in Cepheid SnIa
calibrator data. Here we use Monte-Carlo simulations to show that such a
transition could significantly increase (by a factor of 3 or more) the number
of long period comets (LPCs) impacting the solar system from the Oort cloud
(semi-major axis of orbits $\gtrsim 10^4AU$). This increase is consistent with
observational evidence from the terrestrial and lunar cratering rates
indicating that the impact flux of kilometer sized objects increased by at
least a factor of 2 over that last 100 Myrs compared to the long term average.
This increase may also be connected with the Chicxulub impactor event that
produced the Cretaceous-Tertiary (K-T) extinction of 75% of life on Earth
(including dinosaurs) about 66 Myrs ago. We use Monte-Carlo simulations to show
that for isotropic Oort cloud comet distribution with initially circular
orbits, random velocity perturbations (induced eg by passing stars and/or
galactic tidal effects), lead to a deformation of the orbits that increases
significantly when $G_{\rm eff}$ increases. A 10% increase of $G_{\rm eff}$
leads to an increase in the probability of the comets to enter the loss cone
and reach the planetary region (pericenter of less than 10AU) by a factor that
ranges from 5% (for velocity perturbation much smaller than the comet initial
velocity) to more than 300% (for total velocity perturbations comparable with
the initial comet velocity).
