The lifespans of the most massive stars are a symphony of the
fundamental forces, culminating in a spectacular and violent supernova
explosion. While these events are awesome to observe, they can take a
more sinister shade when they occur closer to home, because an
explosion inside a certain "minimum safe distance" would pose a grave
threat to life on Earth. We will discuss these cosmic insults to life,
and ways to determine whether a supernova occurred nearby over the
course of the Earth's existence. We will then present recent evidence
that a star exploded near the Earth about 3 million years
ago. Radioactive iron-60 atoms have been found in ancient samples of
deep-ocean material, and are likely to be debris from this
explosion. Recent data confirm this radioactive signal, and for the
first time allow sea sediments to be used as a telescope, probing the
nuclear reactions that power exploding stars. Furthermore, an
explosion so close to Earth was probably a "near-miss," which emitted
intense and possibly harmful radiation. The resulting environmental
damage may even have led to extinction of species which were the most
vulnerable to this radiation.