Did exploding stars help life on Earth to thrive?

April 24, 2012, Royal Astronomical Society

An image of the Pleiades (M45), a famous star cluster about 135 million years old. This age means that any massive stars in the cluster would have exploded as supernovae when ammonites were prominent in the sea. According to Henrik Svensmark, the rate of nearby supernovae strongly influenced the diversity of such marine invertebrates. Credit: NASA, ESA and AURA/Caltech
(Phys.org) -- Research by a Danish physicist suggests that the explosion of massive stars – supernovae – near the Solar System has strongly influenced the development of life. Prof. Henrik Svensmark of the Technical University of Denmark (DTU) sets out his novel work in a paper in the journal Monthly Notices of the Royal Astronomical Society.

When the most exhaust their available fuel and reach the end of their lives, they explode as supernovae, tremendously powerful explosions that are briefly brighter than an entire galaxy of normal stars. The remnants of these dramatic events also release vast numbers of high-energy charged particles known as galactic (GCR). If a supernova is close enough to the Solar System, the enhanced GCR levels can have a direct impact on the atmosphere of the Earth.

Prof. Svensmark looked back through 500 million years of geological and astronomical data and considered the proximity of the Sun to supernovae as it moves around our Galaxy, the Milky Way. In particular, when the Sun is passing through the spiral arms of the Milky Way, it encounters newly forming clusters of stars. These so-called open clusters, which disperse over time, have a range of ages and sizes and will have started with a small proportion of stars massive enough to explode as supernovae. From the data on open clusters, Prof. Svensmark was able to deduce how the rate at which supernovae exploded near the Solar System varied over time.

Comparing this with the geological record, he found that the changing frequency of nearby supernovae seems to have strongly shaped the conditions for life on Earth. Whenever the Sun and its planets have visited regions of enhanced star formation in the Milky Way Galaxy, where exploding stars are most common, life has prospered. Prof. Svensmark remarks in the paper, "The biosphere seems to contain a reflection of the sky, in that the evolution of life mirrors the evolution of the Galaxy."

A figure showing the correlation between the rate of nearby supernovae and the diversity of life on Earth. The black curve is the changing rate of supernova explosions in the vicinity of the Solar System over the past 440 million years. The blue curve is the diversity of marine invertebrate animals (number of genera) after subtracting the influence of changing sea-levels. The grey area is an estimate of errors. The scale at the top shows the geological periods (abbreviations for each period are given). Credit: H. Svensmark / DTU Space

In the new work, the diversity of life over the last 500 million years seems remarkably well explained by tectonics affecting the sea-level together with variations in the supernova rate, and virtually nothing else. To obtain this result on the variety of life, or biodiversity, he followed the changing fortunes of the best-recorded fossils. These are from invertebrate animals in the sea, such as shrimps and octopuses, or the extinct trilobites and ammonites.

They tended to be richest in their variety when continents were drifting apart and sea levels were high and less varied when the land masses gathered 250 million years ago into the supercontinent called Pangaea and the sea-level was lower. But this geophysical effect was not the whole story. When it is removed from the record of biodiversity, what remains corresponds closely to the changing rate of nearby stellar explosions, with the variety of life being greatest when supernovae are plentiful. A likely reason, according to Prof. Svensmark, is that the cold climate associated with high supernova rates brings a greater variety of habitats between polar and equatorial regions, while the associated stresses of life prevent the ecosystems becoming too set in their ways.

He also notices that most geological periods seem to begin and end with either an upturn or a downturn in the supernova rate. The changes in typical species that define a period, in the transition from one to the next, could then be the result of a major change in the astrophysical environment.

Life's prosperity, or global bioproductivity, can be tracked by the amount of carbon dioxide in the air at various times in the past as set out in the geological record. When supernova rates were high, carbon dioxide was scarce, suggesting that flourishing microbial and plant life in the oceans consumed it greedily to grow. Support for this idea comes from the fact that microbes and plants dislike carbon dioxide molecules that contain a heavy form of carbon atom, carbon-13. As a result, the ocean water is left enriched by carbon-13. The geological evidence shows high carbon-13 when supernovae were commonest – again pointing to high productivity. As to why this should be, Prof. Svensmark notes that growth is limited by available nutrients, especially phosphorus and nitrogen, and that cold conditions favour the recycling of the nutrients by vigorously mixing the oceans.

Although the new analysis suggests, perhaps surprisingly, that supernovae are on the whole good for life, high supernova rates can bring the cold and changeable climate of prolonged glacial episodes. And they can have nasty shocks in store. Geoscientists have long been puzzled by many relatively brief falls in sea-level by 25 metres or more that show up in seismic soundings as eroded beaches. Prof. Svensmark finds that they are what can be expected when chilling due to very close supernovae causes short-lived glacial episodes. With frozen water temporarily bottled up on land, the sea-level drops.

The data also support the idea of a long-term link between cosmic rays and climate, with these climatic changes underlying the biological effects. And compared with the temperature variations seen on short timescales as a consequence of the Sun's influence on the influx of cosmic rays, the heating and cooling of the Earth due to cosmic rays varying with the prevailing supernova rate have been far larger.

The director of DTU Space, Prof. Eigil Friis-Christensen, comments: "When this enquiry into effects of cosmic rays from supernova remnants began 16 years ago, we never imagined that it would lead us so deep into time, or into so many aspects of the Earth's history. The connection to evolution is a culmination of this work."

Explore further: Fear no supernova

More information: The new work appears in "Evidence of nearby supernovae affecting life on Earth", H. Svensmark, Monthly Notices of the Royal Astronomical Society, in press. The paper can be seen at onlinelibrary.wiley.com/doi/10 … 012.20953.x/abstract and ftp://ftp2.space.dtu.dk/pub/Svensmark/MNRAS_Svensmark2012.pdf

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2.4 / 5 (11) Apr 24, 2012
This is interesting addition to the known modifiers of climate. Unfortunately it does not help with the CO2 disaster we have created.
5 / 5 (6) Apr 24, 2012
"high supernova rates can bring the cold and changeable climate of prolonged glacial episodes"

How? This is not explained in the article.
4.3 / 5 (6) Apr 24, 2012
One of the most intriguing articles I've read on here in a while.

If the data in the supplied graph is accurate it's an amazingly strong correlation.
3.7 / 5 (3) Apr 24, 2012
"high supernova rates can bring the cold and changeable climate of prolonged glacial episodes"

How? This is not explained in the article.

THere is a theory that cosmic rays can trigger cloud formation and that the increased cloud cover would reflect enough sunlight back into space to cause the earth to cool to the point where an ice age is triggered.

Same guy- Henrik Svensmark.
3.7 / 5 (12) Apr 24, 2012
This is interesting addition to the known modifiers of climate. Unfortunately it does not help with the CO2 disaster we have created.

OK, I'll bite. What CO2 disaster?

Measure the CO2 released from Mt St. Helens during its recent large eruption. Now compare this to the yearly human output. A difference of several orders of magnitude, from one eruption. Now look at the yearly geo-chemical contribution compared to mankind's alone. Many orders of magnitude difference to the point where mankind's contribution is lost in the Standard Error of Measurement.

Again I ask, what CO2 disaster?
2.7 / 5 (7) Apr 24, 2012
Undoubtedly this fishing expedition for climate and paleontological effects by a physicist will get ripped to pieces as all other stuff climate denialist Svensmark dreams up.

Pity, because it would have been interesting for astrobiology if true.
2 / 5 (4) Apr 24, 2012
HTML fail: link to Svensmark http://en.wikiped...vensmark .
3 / 5 (10) Apr 24, 2012
@ Shootist:

You are probably trolling, and a climate denialist shouldn't comment on science nor merit a response.

But just in case you are an honest person:

PPhikala is referring to the reigning climate mechanism of AGW, which main driver is anthropogenically produced CO2. This is the current fact and theory found by climate scientists. You can go read more here: http://www.ipcc.ch/ , an intergovernmental non-political panel reviewing the grave process.

Yes, man-made CO2 is a small driver among many, but it is persistent and it is now known to high certainty that it completely predicts the observed temperature increase and no other driver does. And we have been at it for a long time, the current baseline for when it started is pushed back all the time because scientists can observe a larger signal, make better observations and better predictions. Now there are results potentially pointing back to centuries ago.

One off driver or drivers that doesn't go that far? Forget it.
2 / 5 (4) Apr 24, 2012
Yes, man-made CO2 is a small driver among many, but it is persistent and it is now known to high certainty that it completely predicts the observed temperature increase and no other driver does.

Maybe you could graph H2O versus temperature for us?


How about Bright Sunshine? http://i40.tinypi...fyok.jpg

Who thinks increasing sunshine never affects climate?

3 / 5 (6) Apr 25, 2012
@Torbjorn A fact and a theory are 2 different things. The IPCC is a political organization posing as a scientific organization and is heavily influenced by environmental activists running an agenda. It's reports should be treated with contempt. There is no difference between the forcings created by natural and by anthropogenic CO2. CO2 is CO2.
. If you have evidence otherwise please cite it. Now feel free to call me names too
1 / 5 (3) Apr 25, 2012
You are probably trolling, and a climate denialist shouldn't comment on science nor merit a response.

You can't deny climate, lol.

What you can deny, however, is human-caused climate change. The sun is the only reason for the increasing temperatures. The sun has and will always burn in the skies during the day, and will continuously bombard us with more energy every second than humanity will ever need.

If we removed the sun, by climate change believers logic, the earth will still continue to heat up.

I messaged the Aus government and told them that planting trees would be the best way to capture carbon and improve air quality, but their idea of combating it is to simply force people to use less, through means of a "carbon tax". In the process they forget they can use the wood in place of steel and concrete in many homes, they can sell it, or they can turn it into wood chips to be buried in old coal mines which would then be backfilled and restored to original conditions.
3 / 5 (2) Apr 25, 2012
for a more extensive review of this work
not rated yet Apr 26, 2012
Strange idea indeed.

Its a good idea to plant trees to reduce the CO2 amount in the atmoshper... however, dig the wood into the mines is a bit crazy to me ;).... Anyway, there is nothing that man can do to fight with all the other rootcauses of CO2 increase.. and I dont even think, that we should do it.. its simply not worth... every 12k years the climate changes from warm to cold... and I dont think, that 10 or 12k years ago, the human was able to produce so much CO2 to effect the climate....

Anyway.. a nice article.
1.8 / 5 (5) Apr 26, 2012
How ever the amount is certainly higher due to our input...

Unproven assumption. Oceans are the largest store of CO2. The amount in oceans swamps atmospheric CO2.

When natural warming occurs, oceans eventually warm and warm water holds less CO2.

We only have Wild Ass Guesses for carbon transfer from oceans to atmosphere.
5 / 5 (1) Apr 29, 2012

When natural warming occurs, oceans eventually warm and warm water holds less CO2.

Natural Warming. That would also hold true for unnatural or even anthropogenic warming ,Don't you think ? .Noting the care with which you chose your word
5 / 5 (2) Apr 29, 2012
@shootist - Mt St. Helens is estimated to have released ~0.01 gigatons of CO2. That is 3.5 orders of magnitude LESS (~3000 times less) than humans release per year.

@NotParker - we can tell the difference between oceanic CO2 releases and those from fossil fuels - oceanic CO2 still has significant C14, whereas fossil fuel carbon has essentially no C14. (Note that he C14 spike from nuclear weapons testing needs to be taken into account.) And the oceans are still absorbing, rather than releasing, CO2, although that process is slowing down as the oceans warm.

@cc5Delta32- Exactly. This is one of the feedbacks that amplify the modest direct warming effect of CO2 into significant overall warming. NotParker has had this pointed out to him before; that he continues to ignore it shows that he is less interested in truth than in repeating himself.
not rated yet Apr 30, 2012
And what may appear as some interesting scientific research derailed into a "who's to blame" climate discussion. Great!

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