econintersect.com
       
  

FREE NEWSLETTER: Econintersect sends a nightly newsletter highlighting news events of the day, and providing a summary of new articles posted on the website. Econintersect will not sell or pass your email address to others per our privacy policy. You can cancel this subscription at any time by selecting the unsubscribing link in the footer of each email.



posted on 18 July 2017

We Worked Out What It Would Take To Wipe Out All Life On A Planet - And It's Good News For Alien Hunters

from The Conversation

-- this post authored by Rafael Alves Batista and David Sloan, University of Oxford

The first exoplanet was spotted in 1988. Since then more than 3,000 planets have been found outside our solar system, and it’s thought that around 20% of Sun-like stars have an Earth-like planet in their habitable zones. We don’t yet know if any of these host life - and we don’t know how life begins. But even if life does begin, would it survive?


Please share this article - Go to very top of page, right hand side, for social media buttons.


Earth has undergone at least five mass extinctions in its history. It’s long been thought that an asteroid impact ended the dinosaurs. As a species, we are rightly concerned about events that could lead to our own elimination - climate change, nuclear war or disease could wipe us out. So it’s natural to wonder what it would take to eliminate all life on a planet.

To establish a benchmark for this, we’ve been studying what is arguably the world’s hardiest species, the tardigrade, also known as the “water bear" for its appearance. Our latest research suggests these microscopic eight-legged creatures or their equivalents on other planets would be very hard to kill off on any planet that was like Earth. The only astrophysical catastrophes that could destroy them are so unlikely there’s an insignificant chance of them happening. This extreme survival ability adds weight to the idea that life is hardy enough to be found on other planets less hospitable than our own.

Last survivors

Tardigrades are known to survive incredible conditions. Drop the temperature briefly to -272℃ or raise it to 150℃ and they go on. Increase atmospheric pressure to more than 1,000 times that at the Earth’s surface, or drop it to the vacuum of space and they continue. They can survive for up to 30 years without food or water. They can even withstand thousands of grays (standard doses) of radiation. (Ten grays would be a lethal dose for most humans.)

They live all over the planet but can survive far below the ocean’s surface, around volcanic vents at the bottom of the Mariana Trench happily oblivious to the life and death of surface-dwelling mammals. Stripping the ozone layer or upper atmosphere would expose humans to lethal radiation but, at the bottom of the ocean, the water overhead would provide shielding.

Tardigrades: the last survivors? Shutterstock

We wanted to consider what cataclysmic events might be able to finally kill off the hardy tardigrade. What would need to happen to destroy every living thing on the planet? The simplest answer is that the planet’s entire oceans would have to boil. On Earth, this would require an incredible amount of energy - - 5.6 x 1026 joules (around a million years’ of total human energy production at current rates). We therefore have to consider the astrophysical events that could provide such an enormous amount of energy.

There are three primary candidates that could do this: asteroid impacts, supernovae and gamma-ray bursts. Of these, asteroids are the most familiar. We’ve been hit by several over the course of Earth’s history. But, in our solar system there are just 17 candidate objects (including dwarf planets like Pluto and Eris) large enough to provide this energy - and none with orbits coinciding with that of Earth.

By looking at the rate of asteroid impacts on Earth, we can extrapolate the rate at which doomsday events like this would likely occur. This turns out to be approximately once every 1017 years - far longer than the life of the universe. So it’s very, very unlikely to ever happen.

Supernovae (massive explosions of stars) release huge amounts of energy - - 1044 joules, which is more than enough to boil our oceans. Fortunately, the energy delivered to a planet rapidly drops off the further away it is from a supernova. So for the Earth, sterilisation would require a supernova to occur within around 0.013 light-years. The nearest star apart from the Sun, Proxima Centauri, is 4.25 parsecs away(and is the wrong type to go supernova).

For Earth-like planets in our galaxy, the distance between stars depends on their distance from the galactic centre. The central bulge is more densely populated than our neighbourhood. But even closer in, given the rates at which supernovae occur, sterilisation is unlikely to happen more than once in 1015 years, again far beyond the age of the universe.

Finally there are gamma-ray bursts, mysterious explosions producing enormous amounts of energy focused into jets of radiation as narrow as a couple of degrees. Analysing these bursts as we did supernovae, we found that they could only kill off life on an Earth-like planet if their origin was within about 42 light-years and the planet lay within the beam. Again, the rate at which this would occur is sufficiently low that very few planets would ever be sterilised by a gamma-ray burst.

Apocalypse never

Given how tiny the chances are of any of these apocalyptic events actually happening, we’re left with the conclusion that tardigrades will survive until the Sun expands about 1 billion years from now. One final, incredibly unlikely possibility is that a passing star could kick a planet out of its orbit. But, even then, volcanic vents that host some tardigrades could potentially provide heat for long enough for the planet to be captured by another star.

The ConversationThere are many events, both astrophysical and local, that could lead to the end of the human race. Life as a whole, however, is incredibly hardy. As we begin our search for life away from Earth, we should expect that if life had ever begun on a planet, some survivors might still be there.

Rafael Alves Batista, Postdoctoral research associate, University of Oxford and David Sloan, Postdoctoral research associate, University of Oxford

This article was originally published on The Conversation. Read the original article.

>>>>> Scroll down to view and make comments <<<<<<

Click here for Historical Opinion Post Listing










Make a Comment

Econintersect wants your comments, data and opinion on the articles posted. You can also comment using Facebook directly using he comment block below.




Econintersect Opinion








search_box
Print this page or create a PDF file of this page
Print Friendly and PDF


The growing use of ad blocking software is creating a shortfall in covering our fixed expenses. Please consider a donation to Econintersect to allow continuing output of quality and balanced financial and economic news and analysis.







Keep up with economic news using our dynamic economic newspapers with the largest international coverage on the internet
Asia / Pacific
Europe
Middle East / Africa
Americas
USA Government





























 navigate econintersect.com

Blogs

Analysis Blog
News Blog
Investing Blog
Opinion Blog
Precious Metals Blog
Markets Blog
Video of the Day
Weather

Newspapers

Asia / Pacific
Europe
Middle East / Africa
Americas
USA Government
     

RSS Feeds / Social Media

Combined Econintersect Feed
Google+
Facebook
Twitter
Digg

Free Newsletter

Marketplace - Books & More

Economic Forecast

Content Contribution

Contact

About

  Top Economics Site

Investing.com Contributor TalkMarkets Contributor Finance Blogs Free PageRank Checker Active Search Results Google+

This Web Page by Steven Hansen ---- Copyright 2010 - 2017 Econintersect LLC - all rights reserved