The Descent

The  cartographer  pointed  his  pencil  high.  'Up  there  is  another  landmark  invented out   of   Mercator's   imagination.   They   named   it   Polus   Arcticus.   Again,   explorers discovered  the  Arctic  by  relying  on  the  fiction  of  it.  A  hundred  and  fifty  years  later, the  French  cartographer  Philippe  Buache  drew  a  gigantic  –  and  equally  imaginary  – Antarctic   Pole   to   counterweight   Mercator's   imaginary   Arctic.   And   once   again, explorers  discovered it  by  using  a  map  made  of  myth.  So  it  is  with  hell  and  what  you are  about  to  see.  You  might  say  my  mapping  department  has  invented  a  reality  for you to explore.'

Ali  looked  around.  The  one  figure  in  the  audience  that  struck  her  was  Ike.  Her fascination with him was becoming something of an  enigma.  At  the  moment  he  looked singularly odd, wearing sunglasses in a darkened room.

The  old map became a  large  globe  slowly  revolving  behind  the  cartographer.  It  was a  satellite  view,  real-time.  Clouds  flocked  against  mountain  ranges  or  moved  across the blue oceans. On the night side, city lights flared like forest fires.

'We call this Level  1,' said the cartographer. The  globe froze still with the  vast  Pacific facing them. 'Until World War II,  we were  sure the ocean floor was a huge  flat  surface, covered  with a uniform thickness of sea mud. Then radar was invented, and there  was quite a shock in store.'

The  video image flickered.

'Lo and behold, it wasn't smooth.'

A  trillion  gallons  of  water  vanished  in  an  instant.  They  were  left  staring  at  the seafloor,  drained  of  all  water,  its  trenches  and  faults  and  seamounts  like  so  many wrinkles and warts.

'At  great  cost,  Helios  has  peeled  the  onion  even  deeper.  We've  consolidated  an aerial-seismic mosaic of overlapping earth  images. We took every  piece  of  information from  earthquake  stations  and  sonic  sleds  towed  behind  ships  and  from  oil  drillers' seismographs  and  from  earth  tomographies  collected  over  a  ninety-five-year  period. Then  we  combined  it  with  satellite  data  measuring  the  heights  of  the  ocean  surface, reverse-albedo,  gravity  fields,  geo-magnetics,  and  atmospheric  gases.  The  methods have  all  been  used  before,  but  never  all  in  combination.  Here's  the  result,  a  series  of delaminated views  of the Pacific region, layer  by  layer.'

'Now we're  getting somewhere,' one  of  the  scientists  grunted.  Ali  felt  it  herself.  This was big.

'You've  seen seafloor topographies before,' the cartographer  said.  'But  the  scale  was, at best, one to twenty-nine  million.  What  our  department  has  produced  for  Level  2  is almost equivalent to walking on the ocean bottom. One to sixteen.'

He  tapped  a  button  on  his  palm  mouse,  and  the  image  magnified.  Ali  felt  herself shrinking  like  Alice  in  Wonderland.  A  colored  dot  in  the   mid-Pacific  soared   and became a towering volcano.

'This is the Isakov  Seamount, east  of  Japan.  Depth  1,698  fathoms.  A  fathom,  as  you know, equals six feet. We use fathoms for depth readings, feet  for  elevations.  You'll  be using  both.  Fathoms  for  your  position  relative  to  sea  level,  and  feet  to  measure  the heights of cave  ceilings and other subterranean  features.  Just remember  to  convert  to fathoms when you're down there.'

Down there?  thought Ali. Aren't we  already?

The  cartographer  moved  his  mouse.  Ali  felt  flung  between  canyon  walls.  Then  the image threw  them onto  a  plain  of  flattened  sediment.  They  sped  across  it.  'Ahead  lies the Challenger Deep, part  of the Mariana Trench.'

Suddenly  they  were  plunging  off  the  plain  into  a  vertical  chasm.  They  fell.  'Five thousand    nine   hundred    seventy-one    fathoms,'    he    said.    'That's    35,827    feet. Six-point-eight  miles deep. The  deepest  known point on earth. Until now.'

The  image  flickered  again.  A  simple  drawing  showed  a  cross-section  of  the  earth's crust.  'Beneath  the  continents,  the  abyssal  cavities  are  not  exceptionally  deep.  They mostly   exploit   surficial   limestone,   which   is   readily   eroded   by   water   into   such traditional  features  as  sinkholes  and  caves.  These  have  been   the   focus  of  public attention lately  because  they're  close  to  home,  underneath  cities  and  suburbs.  At  last count,  the  combined  military  estimate  of  continental  tunnels  ran  to  463,000  linear miles, with an average  depth of only three  hundred fathoms.