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Recent results have strongly confirmed that multiple supernovae happened atdistances ~100 pc consisting of two main events: one at 1.7 to 3.2 millionyears ago, and the other at 6.5 to 8.7 million years ago. These events are saidto be responsible for excavating the Local Bubble in the interstellar mediumand depositing 60Fe on Earth and the Moon. Other events are indicated byeffects in the local cosmic ray (CR) spectrum. Given this updated and refinedpicture, we ask whether such supernovae are expected to have had substantialeffects on the terrestrial atmosphere and biota. In a first cut at the mostprobable cases, combining photon and cosmic ray effects, we find that asupernova at 100 pc can have only a small effect on terrestrial organisms fromvisible light and that chemical changes such as ozone depletion are weak.However, tropospheric ionization right down to the ground due to thepenetration of $\geq$TeV cosmic rays will increase by nearly an order ofmagnitude for thousands of years, and irradiation by muons on the ground and inthe upper ocean will increase 20-fold, which will approximately triple theoverall radiation load on terrestrial organisms. Such irradiation has beenlinked to possible changes in climate and increased cancer and mutation rates.This may be related to a minor mass extinction around the Pliocene-Pleistoceneboundary, and further research on the effects is needed.

Terrestrial Effects Of Nearby Supernovae In The Early Pleistocene