Mystery of the Giant ExoPlanets --An Update
Holiday 'Galaxy' Insight --"Why the Cosmos, Why the Quantum, Why Existence"

The 30-Million-Year Mass Extinction Cycle --"A Coincidence, or a Dark-Matter Event?" (Holiday Feature)





In 1980, Walter Alvarez and his group at the University of California, Berkeley, discovered a thin layer of clay in the geologic record, which contained an anomalous amount of the rare element iridium. They proposed that the iridium-rich layer was evidence of a massive comet hitting the Earth 66 million years ago, at the time of the extinction of the dinosaurs. The Alvarez group suggested that the global iridium-rich layer formed as fallout from an intense dust cloud raised by the impact event. The cloud of dust covered the Earth, producing darkness and cold, and lead to the extinction of 75% of life on the planet. At first, there was much resistance in the geological community to this idea, but in 1990, the large 100-mile diameter crater produced by the impact was found in Mexico’s Yucatan Peninsula.

The timing of this impact, together with the fossil record, has led most researchers to conclude that this collision caused the mass extinction of the dinosaurs and many other forms of life. Subsequent studies, determined from the record of more than 150 impact craters on the Earth, found evidence for other mass extinctions in the geologic past, which seem to have happened at the same time as pulses of impacts. These coincidences occurred about once every 30 million years. Why do these extinctions and impacts happen with an underlying cycle? The answer may lie in our position in the Milky Way Galaxy.

Our Galaxy is best understood as an enormous disc. Our Solar System revolves around the circumference of the disc every 250 million years. But the path is not smooth; it’s “wavy”. The Earth passes up or down through the mid-plane of the disc once every 30 million years. The cycle of extinctions and impacts is related to times when the Sun and planets plunge through the crowded disc of our Galaxy. Normally, comets orbit the Sun at the edge of the Solar System, very far from the Earth. But when the Solar System passes through the crowded disc, the combined gravitational pull of visible stars, interstellar clouds, and invisible dark matter, disturbs the comets and sends some of them on alternate paths, sometimes crossing the Earth’s orbit where they can collide with the planet.

Recognition of this 30 million year Galactic cycle is the key to understanding why extinctions happen on a regular schedule, but it may also explain other geologic phenomena as well. In further studies, it was found that a number of geological events, including pulses of volcanic eruptions, mountain building, magnetic field reversals, climate and major changes in sea level, show a similar 30 million year cycle. Could this also be related to the way our Solar System travels through the Galaxy?

A possible cause of the geological activity may be interactions of the Earth with dark matter in the Galaxy. Dark matter, which has never been seen, is most likely composed of tiny sub-atomic particles (Weakly Interacting Massive Particles or WIMPS) that reveal their presence solely by their gravitational pull. As the Earth passes through the Galaxy’s disc, it will encounter dense clumps of dark matter. Physicists have argued that the dark matter particles can be captured by the Earth, and will build up in the Earth’s core. If the dark matter density is great enough, the dark matter particles eventually annihilate one another, adding a large amount of internal heat to the Earth that can drive global pulses of geologic activity.

Dark matter is concentrated in the narrow disc of the Galaxy, so geologic activity should show the same 30 million year cycle. Thus, the evidence from the Earth’s geological history supports a picture in which astrophysical phenomena govern the Earth’s geological and biological evolution.

The Daily Galaxy via Michael Rampino/Oxford University Press 


This reminds me of an article in Nature in March 2005 by Richard Muller and Robert Rhode entitle “Cycles in fossil diversity”.

Muller and his grad student used a database created by the late University of Chicago paleontologist Jack Sepkoski. Entitled "Compendium of Fossil Marine Animal Genera", Sepkoski’s database is the most complete reference available for the study of biodiversity and extinctions.

They found that an analysis of the fossil records of marine animals over the past 542 million years suggested that biodiversity appears to rise and fall in mysterious cycles of 62 million years for which, at the time or their paper, science had no satisfactory explanation.

The 62 million year fossil diversity cycle was most evident in the historical records of genera that survived less than 45 million years. Some organisms seem to be immune to the cycle, while others are exceptionally sensitive. For example, corals, sponges, arthropods and trilobites follow the cycle, but fish, squid and snails do not. In general, longer-lived genera that are more diverse and widespread stand a better chance of resisting the 62 million year cycle.

While the history of life on Earth appears to be shaped by a 62 million year cycle, nothing in present evolutionary theory accounts for it. The declines in the 62-million-year cycle correspond with some of the best known mass extinctions on Earth. Muller believes the pattern is too regular to occur by chance.

They examined 14 possible geophysical and astronomical causes of the 62 million year cycles, but no clear explanation emerged. This included asteroid and comet impacts, global climate shifts, volcanic eruptions, fluctuating sea levels, changes in the total amount of plant and animal life, and the reshuffling of the continents. Muller believes the pattern is too regular to occur by chance.

In 2010 Adrian Melott and Richard Bambach confirmed that extinctions occur every 27 million year with a confidence level of 99%. ("Nemesis Reconsidered", Monthly Notices of the Royal Astronomical Society Letters 407, L99-L102 (2010))

in April 2007, Mikhail Medvedev and Adrian Melott presented a theory that a 26 million year cycle was caused by cosmic rays. ("Do extragalactic cosmic rays induce cycles if fossil diversity?", The Astrophysical Journal, August 2007) They observed the Sun regularly moves up and down through the thin portion of the galactic disk. It reaches its farthest distance from the central plane every 62 million years (230 million light years above the disc, which means it is moving through the center of the disc every 30 million years or so.

The important question to answer it seems is where is the Sun now and how long until the next cataclysmic event

(230 million light years above the disc, which means it is moving through the center of the disc every 30 million years or so.

Anybody proof read these articles???????

Dam that means we are due or should I say doomed

Hmm, I try and think that I can at least be a little logical, at times. So, if we can define the period that the sun is making through its path above and below the disc that they speak of, how can the important question be where is the sun now? I would think that be known as part of the process of determining the cycle. I guess I can excuse the 230 million light years above the disc as some type of typo that needs to be corrected. If that were true, then I think the greatest piece of information would be the fact that we are traveling over 5 times the speed of light, lol.

Knowing the cycle, from historic data, of the 'effects' would not necessarily pinpoint where in the cycle of movement Sol is. Are we moving into the disk, out, right in the middle, etc? That is the determination to which the article is referring. Then knowing the sun's current status in the cycle would highlight what conditions might cause the extinction and geologic cycles. My question is similar though from a different angle. I was under the impression that the position of Sol in its galactic oscillation cycle was known. I could find no reference material to that fact, though. So, where is Sol in the cycle?

I suspect the next mass extinction event will not be triggered by any of the above factors but caused by one of its casualties and that is us.

Here's a link to a NewScientist article about this cycle (

The author claims:
1. Solar System bobs up and down through central disc every 60 million years
2. The apogee (top of the bob both up and down) is 200 light years
3. The Solar System is now out of the central disc and is increasing it's distance in the "Northern (above?) the Milky Way.

The 6th great mass extinction, since the beginning of the Cambrian, is ongoing right now. It is called the Anthropogenic Mass Extinction and it will be a doozy!

Many errors. There are two components:
1. 62 Myr period in biodiversity
2. 27 Myr period in extinction rate.
Note that these are not in phase. So they are probably unrelated.
Medvedev and Melott commented on #1. Not "26".
The distance is not 230 million light years above the disk!
This article is so confused and full of errors that I would not try to straighten it out.

Correct me if i am wrong, but the Yucatan impact that killed the dinosaurs was approximately 65 million yrs ago... so unless there was one of these catastrophic events approximately 3 million yrs ago, then we are a few millions of years of over due.

if there was a mass extinction 65 m yrs ago and the period is 30 m yrs, what the the mass extinction event 35 m yrs ago?

Verify your Comment

Previewing your Comment

This is only a preview. Your comment has not yet been posted.

Your comment could not be posted. Error type:
Your comment has been posted. Post another comment

The letters and numbers you entered did not match the image. Please try again.

As a final step before posting your comment, enter the letters and numbers you see in the image below. This prevents automated programs from posting comments.

Having trouble reading this image? View an alternate.


Post a comment

Your Information

(Name is required. Email address will not be displayed with the comment.)