Gamma Ray Bursts as a Possible Cause of Extinctions

Quick explanation

In the 90's astronomers discovered intense beams of gamma rays (more powerful than x-rays) coming from the north and south poles of certain kinds of supernovas. These laser like beams of radiation could deliver a large dose of radiation over a much greater distance than the explosion of the supernova itself. There is much debate over the frequency of these types of explosions, and how close they would have to be in order to penetrate our protective atmosphere. My research looks for radiation effects in the fossil record. This is considered fringe science by professional paleontologists but is a serious study in astronomy. Since I am the only person that is a member of both the American Astronomical Society and the Society of Vertebrate Paleontologists, I am in a unique position to study this problem.


Recent discovery of huge bursts of radiation

While TV shows endlessly portray asteroids slamming into the Earth and wiping out all living things, most professional paleontologists remain "uncomfortable" with the theory. This is based on the fact that the asteroid didn't kill off everything it should have. This is known as "the pattern of extinction problem" for which there is presently no clear answer. Everything on land over 50 lbs died but small animals survived. In the oceans it was different with the surface dwelling organisms like plankton getting harder hit than the deep ocean creatures.

In the mid 90's a major discovery in the field of supernova astronomy called the Gamma Ray Burst, opened up the possibility of a brand new extinction mechanism. It was discovered that there were special types of supernovas that put out huge amounts of gamma radiation. Gamma rays are much more powerful than x-rays and for 30 years gamma ray flashes were detected by various satellites in orbit. These GRB's (Gamma Ray Bursts) were thought to be weak and close by in our galaxy. This new discovery proved that these radiation flashes were EXTREEMELY powerful and coming from the other side of the universe! These explosions were so big it was equivalent to transforming our entire Sun into pure energy in 10 seconds.

Astronomers puzzled over this as more data came in. Eventually they came to understand that the flash of gamma rays is beamed out the poles of certain types of supernova explosions forming a laser like beam of radiation. If this beam is pointed at us we can see it like a laser, very far away and this accounts for its apparent intensity. On average we detect one of these gamma ray beams from somewhere in the universe every day.


Could it hits us?

So the next question is, what would happen if a Gamma Ray Burst exploded in our galaxy and was pointed at us? This is discussed openly in professional astronomy circles but is relatively unknown in paleontology. Paleontology subscribes to the "gradualist" theory of evolution and catastrophic ideas are usually discounted off hand because in the past so many have been rejected on closer inspection.

Our atmosphere and particularly the ozone layer protect us from space radiation. Exactly how much protection this affords us seems to be a difficult question to answer. If the Gamma Ray Burst was close enough we would be cooked but the closer it is, the more the odds are against it happening.


Odds of a supernova

Regular supernovas (no gamma rays) were originally considered as a extinction candidate before we knew about Gamma Ray Bursts but were dismissed because they would have to be too close in order to do any real damage. We can calculate the number of stars in our galactic neighborhood and how often they would come close to our solar system. On average a supernova goes off in our galaxy every 150 years or so. Calculating our proximity to other stars, and how often they blow up, the odds of a generic supernova going off close enough to hurt us is low.

For reference it is estimated that a supernova goes off in the universe at a rate of one a second while a GRB supernova happens much less frequently at 500 times a day. The Gamma Ray Burst can deliver much higher radiation levels over a longer distance because of its beaming characteristics but they happen less frequently and have to be pointed right at us. This is one of the areas of contention in these debates. I am not knowledgeable enough to determine these parameters so my work involves looking for artifacts in the fossil record that could be caused by radiation overdose.


Thoughts on causes of extinctions

Exactly what causes major extinctions remains unclear and there are over 5000 papers published on the subject. Since so much time and effort has been spent researching this area, the answer is certainly not simple. My personal speculation is that either extinctions are caused my multiple overlapping events that after the fact can not be sorted out or from some yet unknown process. Since the GRB is the only new extinction mechanism to come along in a while, I believe its worth investigating.


Interesting facts that could be associated with a radiation event.

Ionizing radiation has three effects on organisms death, sterilization and mutation. As far as paleontology is concerned, death and sterilization are the same since the organism can't propagate. Gamma rays are high energy photons and shining them around the environment is equivalent to trying to detect a flashlight shined around the room last week. The characteristics I am looking for are groups of organisms that exhibit high or low radiation resistance, strange variations in mutation rates and secondary reactions from radiation.


Interesting fossil record observations in context with radiation overdose.

PATTERN OF EXTINCTION: All animals over 50 lbs died at the KT boundary while smaller ones survived. Pro, large animals are more sensitive to radiation exposure and die at lower exposure doses than smaller ones. Cold bloods exhibit higher resistance than warm bloods giving crocks and turtles the edge despite their larger size. Con, no explanation is currently popular in the paleo community to explain this observation.

REVERSE EFFECTS IN THE OCEAN: 30 feet of water offers as much radiation protection as the atmosphere above. Surface organisms would be more affected than bottom dwellers. Con, no good current explanation for this observation.

POLLEN MISSING IN IRIDIUM LAYER: Close examination of the fallout layer at the KT boundary shows that all pollen is missing except for fern pollen. If the asteroid hit a pristine environment the fallout layer should have included all the pollen. If a GRB wiped out life first and was closely followed by the asteroid impact, the result would be multiple overlapping scenarios as postulated above. Con, the iridium may have stayed suspended in the atmosphere longer and settled to the ground long after the event.

IMPACTS ASSOCIATED WITH SOME BUT NOT ALL EXTINCTIONS: An interesting talk given at the 191st AAS meeting described the effect a GRB would have on the Ort Cloud which holds our supply of comets. The GRB would heat one side of the comets perturbing their orbits. This disturbance would send a swarm of comets into the inner solar system. If this were true, then you would expect to see impacts immediately following extinction in some but not all events. This is interesting because it would allow the impact scenario to remain intact inside the larger GRB event. Pro, comet swarms have been detected using Helium3 at the Eocene/Oligocene boundary. Con, Helium3 measurements at the KT boundary show no swarm.

CAMBRIAN EXPLOSION EXTINCTION EVENT?: The Cambrian Explosion saw a sudden explosive diversity of small multicellular species into organisms that formed the basis for most of today's evolutionary families. Pro, a GRB during this period in time would not have had any large animals to kill off. The radiation event would have induced mutations in the whole gene pool. Under these circumstances you would only see sudden widespread mutations that would fill the available niches. Con, as life developed on the planet at some point it would be expected that life forms would invade a new unoccupied niche and rapidly diversify. An example being the transition from water to land.

MOLLECULAR CLOCKS: There is a current ongoing controversy between molecular biologists and paleontologist over the divergence times of major species. The biologists can read the gradual accumulation of mutations in DNA that happen at a steady pace over time. This allows them to extrapolate backwards to when the two species had a common ancestor. Paleontologists do the same thing by finding direct fossil evidence. The argument stems from the fact most of the divergence times calculated by the DNA clocks are much older than the fossil evidence. Pro, a large percentage of mutations in DNA are caused by background radiation in our environment. A Gamma Ray Burst would induce extra mutations into the entire existing gene pool at a moment in time. This would make it look like the molecular clocks had extra ticks leading to the conclusion that the divergence was farther back. Con, not all of the divergence times are older. The fossil record is poor in most cases and may not show the proper divergence from fossils alone. The molecular clock dating method is relatively new and may get more accurate over time.