If you won't look, how about I shove it into your face because you won't look for yourself.

Abstract

The Solar System during its life has travelled more than 10 times through dense interstellar clouds with particle concentrations of 102-103 and more, compressing the heliosphere to heliopause dimensions smaller than 1 AU and thus bringing the Earth in immediate contact with the interstellar matter. For cloud concentrations greater than of 102 , the flowing interstellar material even at the Earth`s orbit remains completely shielded from solar wind protons and would only be subject to solar photoionization processes. We have developed a 2D-two-fluid gas-dynamical numerical code to describe the hydrodynamical behavior of the incoming interstellar gas near the Earth, taking into account both the photoionization and the gravity of the Sun.

As we show, the resulting strongly increased neutral hydrogen fluxes ranging from 109 to 1011 cause substantial changes in the terrestrial atmosphere. During the phase of the immersion into the cloud the resulting flux of neutral hydrogen incident on the terrestrial atmosphere in the steady state would be balanced by the upward escape flux of H-atoms and the downward flux of water molecules, which is the product of the atmospheric hydrogen-oxygen chemistry via even-odd reaction schemes. In that case hydrogen acts as a chemical agent to remove oxygen atoms and to cause ozone concentration reductions above 50 km by a factor of 1.5 at the stratopause to about a factor of 1000 and more at the mesopause. Thus, depending on the specific encounter parameters the high mixing ratio of hydrogen in the Earth's atmosphere may substantially decrease the ozone concentration in the mesosphere and may trigger an ice age of relatively long duration.
[link to astro.uchicago.edu]

Plenty more there. Many different models showing the effects of different clouds.

Eons ago, giant clouds in space may have led to global extinctions, according to two recent technical papers supported by NASA's Astrobiology Institute.

One paper outlines a rare scenario in which Earth iced over during snowball glaciations, after the solar system passed through dense space clouds. In a more likely scenario, less dense giant molecular clouds may have enabled charged particles to enter Earth's atmosphere, leading to destruction of much of the planet's protective ozone layer. This resulted in global extinctions, according to the second paper. Both recently appeared in the Geophysical Research Letters.

"Computer models show dramatic climate change can be caused by interstellar dust accumulating in Earth's atmosphere during the solar system's immersion into a dense space cloud," said Alex Pavlov, principal author of the two papers. He is a scientist at the University of Colorado, Boulder. The resulting dust layer hovering over the Earth would absorb and scatter solar radiation, yet allow heat to escape from the planet into space, causing runaway ice buildup and snowball glaciations.

Moderately dense space clouds are huge, and the solar system could take as long as 500,000 years to cross one of them. Once in such a cloud, the Earth would be expected to undergo at least one magnetic reversal. During a reversal, electrically charged cosmic rays can enter Earth's atmosphere instead of being deflected by the planet's magnetic field.
[link to www.nasa.gov]

Now maybe they didn't teach you such complicated things in your geology major or these discoveries were made after you finished learning. But there is plenty of geological evidence for this from the ice core samples which shows the atmospheric density and composition, as well as cosmic ray flux to tree rings and geological features.