Exploding star strafed Earth

A supernova is the death throes of a large star <br>© NASA <br>

A supernova may have caused mass extinction two million years ago.

The explosion of a dying star could have ended much of marine life on Earth two million years ago. The supernova could have strafed the Earth’s atmosphere with cosmic rays, severely damaging the ozone layer and exposing living organisms to high levels of the Sun’s hazardous ultraviolet rays, US researchers propose1.

This idea dates back to the 1950s, but now Narciso Benítez of Johns Hopkins University in Baltimore, Maryland, and colleagues have come up with the first plausible evidence. Their proposal remains tentative, but is consistent with what is known about the likelihood of nearby stellar explosions and the telltale signatures of these events on our planet.

Supernovae are the death throes of large stars. When such stars run out of fuel for nuclear fission, they collapse under their own gravity, heat up rapidly and explode, releasing huge amounts of matter and energy. Fortunately for us, such outbursts are rare: the most recent one in our own galaxy was spotted in 1604, and was too far away to pose any risk. Several supernovae have been observed more recently in other galaxies.

One-fifth of all supernovae occur in large groups of relatively young stars that are thought to have coalesced from the same gas cloud. One such cluster in our own galaxy is the Scorpius-Centaurus association, which comprises three subgroups of stars.

Each subgroup would have generated supernovae at different times: about 10, 7 and 2 million years ago, say Benítez’ group. The most recent episode could have included a supernova as little as 130 light years from Earth. This is not close enough to fry our planet. But it would have left a mark that the researchers think has already been found.

Three years ago, scientists in Germany reported high concentrations of iron-60 in two layers of ocean rock, dated at about 0-3 and 4-6 million years old2. Iron-60 is a rare form produced on Earth by nuclear reactions involving cosmic rays, such as those that supernovae generate.

Putting these arguments together, Benítez’ team proposes that the most recently formed iron-60 layer could be the result of a nearby supernova in the Scorpius-Centaurus association around two million years ago. The supernova could have left another signature – in the fossil record.

Two million years ago, many marine creatures, such as bivalve molluscs, died out suddenly all over the planet. As mass extinctions go, this was a mild one. But no one knows what caused it.

Benítez and his colleagues think that a nearby supernova at this time could have showered the Earth with cosmic rays. These charged subatomic particles collide with atoms in the air, initiating chemical reactions. Copious cosmic rays are thought to produce nitrogen monoxide, which can destroy ozone molecules.

The researchers calculate that a supernova 130 light years away could have thinned the ozone layer by up to 60 per cent, exposing marine organisms to ultraviolet rays from the Sun. This could have killed off plankton, and thence the molluscs that live off them.

To support this hypothesis, astronomers now need to find the smoking gun: remnants of ancient supernovae in nearby star clusters.

References

  1. Benítez, N., Maíz-Apellániz, J. & Canelles, M. Evidence for nearby supernova explosions. Physical Review Letters, 83, 081101, (2002).
  2. Knie, K. et al., Indication for supernova produced 60Fe activity on Earth. Physical Review Letters, 83, 18 – 21, (1999).

Media Contact

PHILIP BALL © Nature News Service

All latest news from the category: Physics and Astronomy

This area deals with the fundamental laws and building blocks of nature and how they interact, the properties and the behavior of matter, and research into space and time and their structures.

innovations-report provides in-depth reports and articles on subjects such as astrophysics, laser technologies, nuclear, quantum, particle and solid-state physics, nanotechnologies, planetary research and findings (Mars, Venus) and developments related to the Hubble Telescope.

Back to home

Comments (0)

Write a comment

Newest articles

Superradiant atoms could push the boundaries of how precisely time can be measured

Superradiant atoms can help us measure time more precisely than ever. In a new study, researchers from the University of Copenhagen present a new method for measuring the time interval,…

Ion thermoelectric conversion devices for near room temperature

The electrode sheet of the thermoelectric device consists of ionic hydrogel, which is sandwiched between the electrodes to form, and the Prussian blue on the electrode undergoes a redox reaction…

Zap Energy achieves 37-million-degree temperatures in a compact device

New publication reports record electron temperatures for a small-scale, sheared-flow-stabilized Z-pinch fusion device. In the nine decades since humans first produced fusion reactions, only a few fusion technologies have demonstrated…

Partners & Sponsors