There is currently no scientific consensus on the cause of the late Ordovician mass extinction–one of the five biggest in Earth’s history–approximately 440 million years ago. Several theories have been proposed, including volcanic activity, climatic changes, and asteroid impacts, but a gamma-ray burst (GRB) is not generally considered a leading hypothesis for this extinction event. {Nasa}
GRBs are incredibly powerful. In a few seconds they can emit as much energy as the sun will emit over its entire 12-billion-year life span. {SciAm} These cosmic blasts are the most powerful explosions in the Universe and short-lived bursts of gamma radiation that can, potentially, cause significant damage to life on Earth. One astronomer at the University of Kansas in the USA, Dr. Adrian Melott, told the BBC for an article published in 2005 that a GRB originating within 6,000 light years from Earth could devastate life on Earth. For example, a 10-second burst close enough to the Earth could deplete up to half of the planet’s ozone layer. {BBC}
However, as of 2023, there is no strong evidence linking a GRB to the Ordovician extinction. GRBs are typically associated with high-energy astrophysical events such as supernovae or the collision of neutron stars, which are not well correlated with the timing of the Ordovician extinction.
In 2017 an analysis at Washburn University by astrophysicist Brian Thomas showed that even if a GRB hit the Earth at a most vulnerable latitude, striking one of the poles, the maxium ozone formed on the ground would be 10 ppb, a third of the 30 ppb which would cause increased risk of death due to respiratory failure in humans. {SciThink}
Scientists are continually studying the Ordovician extinction and exploring various potential causes. Future research might uncover new evidence that could support or alter our understanding of the event’s cause, but as of now, a gamma-ray burst is not considered a primary suspect.
What is the Risk?
Scientists estimate that the Earth is relatively safe from GRBs since they originate from distant supernovae or black hole mergers. The probability of a significant GRB occurring nearby and posing a threat to Earth is considered extremely low.
Stars capable of causing a Gamma-Ray Burst (GRB) are typically extremely far away from Earth. GRBs are believed to be produced by the collapse of massive stars or the merging of binary neutron star systems, which occur in distant galaxies. At one point the closest known GRB to Earth occurred in 2008 and was located approximately 7.5 billion light-years away. Therefore, the stars that can cause GRBs are located at vast distances in the universe.
Early in October 2022, however, a wave of high-energy radiation swept over Earth from a gamma-ray burst. Astronomers quickly determined its distance, two billion light-years from Earth, the closest such burst ever seen of over 1700 observed at the time. However, “close” is in relative astronomical terms. This distance is immense in human terms and is even a decent fraction of the size of the observable universe.
An astrophysicist, Rami Mandow, pointed out that lightning detectors in both India and Germany showed that the way pulses of electromagnetic radiation from lightning propagated had changed suddenly at the same time the GRB energy hit our planet. The pulses indicate conditions in Earth’s upper atmosphere changed, as electrons were suddenly stripped from their host atoms. Gamma rays do ionize atoms in this way, so it seems very likely that energy from this GRB 2 billion light years away did physically affect our planet’s atmosphere, though only mildly and briefly. It was also an excellent opportunity for scientists to learn more about these phenomena.
