Search This Blog

Saturday, 14 July 2012

The ocean from the sky....

How's my blogging? Leave some feedback, I get better at this, you get a better read!

It's post 100! What am I doing to celebrate.... ? Writing post 101. Because, frankly, just being alive at a time the human race knows about these places is privilige enough!

Water water everywhere. Anyone in Manchester city centre yesterday would have agreed with that. But why is that so? Earth started out as a blob of molten rock – so why would there be so much water here?

Video above: The beginnings of the Earth - a ball of magma, with a core as hot as the Sun. Any water it had was chemically bound in hydrated minerals. The raindrops, falling on your head? They're miraculous. Video courtesy of the BBC. 

Water has two chemical ingredients, hydrogen and oxygen, and they would have been abundant. So some of the gas erupted through the newly formed crust would have been water vapour. As the temperature dropped still further the vapour would have condensed, and eventually fallen as rain. Lots and lots of rain. Non-stop, worldwide, rain. For thousands of years at least.

Enough rain to make a British summer look Mediterranean.

There's a problem with that though: Do the maths on how much water you get this way, and it's hard to get all water we see on Earth today* what about the rest of it?
The leading theory is that the extra water, a lot of the other volatiles [1] and some of the organic (carbon bearing, life related, but not living) materials were delivered by either comets [2], or volatile rich asteroids [3]. When I say ‘delivered’…. you've seen asteroid disaster movies, right? So when I say delivered.... Post van crashing into your front room, on fire, delivered…… but the volatiles arrived with either asteroids or comets, that’s the point.

Video above: A quick run down on where scientist think the oceans of Earth came from - their best guess at the moment, based on all the evidence we can find. Never trust someone who claims to know the answer to such a huge mystery with total certainty. Or a man offering you sweets to get into his car. Not even if you're thirty five. Video courtesy of National Geographic.

Our current ideas [4] on how the solar system formed predict that volatile rich asteroids, and comets, formed waaaaay out, in the deep freeze of the outer solar system. That would make the realm of Pluto and Sedna [5] the ultimate source of the oceans of Earth.

Video above: The discovery of the first Kuiper belt object bigger than Pluto - the first of many, which gives you an idea of just how much ice there is out there... Video courtesy of the BBC.

Which is an idea that needed testing - so researchers, from the Carnegie Institute for Science, did [6]. They used a method that's down to an isotope of hydrogen - deuterium [7].

We're pretty sure that the carbonaceous chondrite meteorites [8] are chunks from volatile rich asteroids -  they contain traces of water and organic compounds. The ratio of deuterium to ordinary hydrogen, in their water, should be higher the closer to the Sun they formed. The same trick works on comets.

The Carnegie team carefully measured the deuterium content of water, found inside eighty six carbonaceous chondrites, and compared that to space craft data from comets. They saw how well the ratios matched to each other, and to the deuterium ratios in water on Earth....... And the universe surprised them! The asteroids and comets have different ratios. To explain this the Carnagie team suggest that the water rich asteroids formed in the outer edge of the asteroid belt, whereas the comets formed far further into space.
What's more, the asteroid ratios were a far better fit to terrestrial water. The team were able to confirm their findings with a similar trick, using nitrogen and its isotopes this time. So the asteroids are the most likely source for our oceans - and our models of the solar systems formation need adjusting.

This is not the first time that asteroids have been suggested as a source of our oceans. In 2010 a two hundred kilometre wide asteroid, twenty four Themis, was examined in infra red light. Its spectrum showed it was coated in a layer of water ice frost [9], and had organic material on its surface [10]

Image above: A computer simulation showing the main belt asteroids in white, and the Trojan asteroids that follow Jupiter around in green. The orbit of the asteroid Themis is highlighted in red, on the outer edge of the main belt. Image courtesy of Josh Emery/University of Tennessee, Knoxville.

The finding was a huge surprise: Themis is near the outer edge of the asteroid belt, but it still receives enough sunlight that water ice on the surface should sublimate away into space. The only plausible explanation, for how the huge space rack keeps its frosty coat, is a massive internal reserve of water -  perhaps as much as twenty or thirty percent by weight. That's a staggering amount  [11] - millions of cubic kilometres. Bombardment [12] by asteroids of a similar composition to Themis could have supplied early Earth with every thing needed to get simple life going, even if the blasts threw much of the water back into space.

Video above: A run down on the discovery that Themis has organic molecules and water ice frost on it's surface - which probably means a huge reservoir of ice and organics inside.Video courtesy of the American Museum of Natural history.

Discoveries like these have made carbon and water rich asteroids high on the list of priorities for astrobiologists, and space exploration agencies in general. The Japanese JAXA agency is launching the Hayabusa two [13] mission in 2014, with the goal of returning a sample of such an asteroid to Earth. And carbonaceous chondrites continue to surprise us [14], with a bewildering variety of molecules [15] related to the origins of life. 

So go and take a look in the mirror: The human body is seventy five percent water, and based around organic (carbon) chemistry. 

Which means that parts of you have come a very, very, long way to be here......

*And there's a lot more [16] than you can see...

List of links:

No comments:

Post a Comment