Astronomy

WWW.ASTRONOMY.COM 45

Anyone who could reason and keep records would notice that the
rate of lightning has increased a lot.
The lightning ignites fires. In the Great Rift Valley in East
Africa, where humans’ ancestors are living, forests are converted
to grassland, forcing inhabitants to walk from tree to tree. There
may be long pauses between periods of increased lightning activ-
ity, so the area transitions from grassland to scrub and back again,
challenging these early humans to adapt.

What happened?

I’ve written about the generalized threat from astrophysical radia-

tion events. Nearly all the work in this field has been a “what if ”

game. Scientists know there must have been radiation events,

just based on the odds. From astronomical observations, we can

infer the average rate of supernovae, gamma-ray bursts, and solar

outbursts. From this rate, we can infer the likelihood of such an

event close enough and powerful enough to affect life on Earth.

A bright supernova

in our sky would do

much more than cast

shadows at night.

It would rain down

devastating radiation

that could alter

life on our planet.

RON MILLER FOR ASTRONOMY