There are two parts to the question, the first concerning the conjecture that there may have been significant changes, more particularly increases in Earth's 'gravity'--thus acceleration due to gravity g-- over geological time, the second some speculation about the implication of relatively acute changes in gravity in such mass extinction events as that arising at the KPg boundary (and not excluding the idea that such acute increases might indeed be periodic in geological history; as in the earlier instance of the 'great rainforest collapse' in which several factors may have been implicated militating against the capacity for huge vegetative organisms to sustain height under phototropic impetus).
With respect to the first part, and in answer to the response to it that no evidence of such increase exists, might I humbly suggest that demise of non-avian dinosaurs in particular, massive creatures on a boggy Earth, does in fact of itself constitute reasonable evidence of such increase regardless of suppositions about the cause of that change in gravity; more especially since dinosaur extinction cannot reasonably be ascribed entirely to the effects of the Chicxulub impact, even in association with the atmospheric effects of the Deccan traps.
These latter hypotheses require the scarcely credible conclusion that not one single solitary breeding pair of young dinosaurs of the billions extant at the time were able to endure a year or two of privation, subsisting on hay in some cosy valley somewhere; or have managed to sustain themselves through epigenetic adaptation in an atmosphere corrupted by volcanic ash. Any reasonable analysis of the evidence of this extinction clearly suggests the involvement of another factor; and some such increase in gravity, especially if it were able to be otherwise corroborated, should be far more seriously considered than is apparent from the almost hysterical indignation evinced at this site.
Regarding the cause or mechanism of such an abrupt (periodic) increase in g, this is indeed a difficult question; but its answer most certainly does not devolve upon speculation about the mass of the Earth whose estimation depends primarily on assumptions in gravitational theory contingent upon measures of g. The objection that gravity cannot have changed because the Earth's mass has not substantially varied is obviously circular and invalid. One is left to imagine various scenarios in which proximity to the Sun or to bodies such as the Moon may have changed.
In considering the composition of atmospheric gases as corroborative evidence for such an increase in gravity (and noting the nature of the course of such changes), the relative mass of the atmosphere as a whole is immaterial. The issue is whether an increase in g may have favoured the incorporation of heavier gases like CO2 and O2 into carboniferous biomass or mineral oxides as the function of their molecular weights, conversely allowing lighter gases and H2O to escape into the atmosphere through displacement. This is clearly a difficult and contentious point, but it warrants proper reasoned scientific consideration, rather than the puerile repudiation of the entire sense of the question by those who seem not to have understood it; and indeed to have responded rather dismally by viciously down-voting it under the cloak of privilege.
Possibly I might have framed the question differently, or even asked separate questions had I not been perhaps naively encouraged by the belief that those purporting to be scientists at this site would be capable of accommodating several related lines of inquiry simultaneously, and of responding to a well-considered question asked in good faith with proper diligence.