NEWS

F

or our Australopithecus ancestors

who roamed Africa 2.5 million

years ago, the bright new star in

the sky surely would have aroused

curiosity. As luminous as the full

Moon, it would have cast shadows

at night and been visible during the

day. As the supernova faded over

the following months, it probably

also faded from memory. But it left other

traces, now coming to light.

Over the past 2 decades, researchers

have found hundreds of radioactive atoms,

trapped in seafloor minerals, that came

from an ancient explosion marking the

death of a nearby star. Its fusion fuel ex-

hausted, the star had collapsed, generating

a shock wave that blasted away its outer

layers in an expanding ball of gas and dust

so hot that it briefly glowed as bright as

a galaxy—and ultimately showered Earth

with those telltale atoms.

Erupting from hundreds of light-years

away, the flash of x-rays and gamma rays

probably did no harm on Earth. But the

By Daniel Clery

FEATURES

STARSTRUCK

SCIENCE sciencemag.org 16 JULY 2021 • VOL 373 ISSUE 6552 269

Atomic traces left by nearby supernovae point to ancient assaults on Earth

The Crab nebula

is the remains of a

supernova more than

6000 light-years

away—too far to

harm Earth.

PHOTO: NASA; ESA; J. HESTER AND A. LOLL/ARIZONA STATE UNIVERSITY

0716NewsFeatures.indd 269 7/12/21 5:30 PM