• 
  Ezra Knight

  (17 episodes, 2013-2014)
• 
  Trevor Valle

  Self - Wildlife Biologist
• 
  David Aguilar

  Self - Astrophysicist, Harvard Smithsonian
• 
  Brandon Browne

  Self - Volcanologist, CSU Fullerton
• 
  Jim Cantore

  Self - Meteorologist
• 
  Brent Christner

  Self - Microbiologist, LSU
• 
  Simon Donner

  Self - Climate Scientist, University of BC
• 
  Dalvin Etsitty

  Self - Guide, Antelope Canyon Navajo Tours

• 
  Jim Faulds

  Self - Geologist, Univ. of Nevada, Reno
• 
  Victor Ferrell

  Self - O.X. Excursions Guatemala
• 
  Dean Gallagher

  Self - Hawaii Volcanoes National Park Ranger
• 
  Tim Garrett

  Self - Atmospheric Scientist, Univ. of Utah
• 
  Chris Goldfinger

  Self - Oceanographer, Oregon State University
• 
  Gannet Hallar

  Self - Director, Storm Peak Laboratory
• 
  Joseph Henton

  Self - Geophysicist, Natural Resources Canada

• 
  Brian Killett

  Self - Geophysicist, NASA-JPL
• 
  Michio Kaku

  Self - Theoretical Physicist
• 
  Alex Filippenko

  Self - Astrophysicist, UC Berkeley
• 
  Chris McKay

  Self - NASA Astrobiologist
• 
  Reynolds Wolf

  Self - Meteorologist
• 
  Peter Ward

  Self - Paleontologist, Univ. of Washington
• 
  Daniel Lathrop

  Self - Geophysicist, Univ. of Maryland
• 
  Costas Emmanuel Synolakis

  Self - Coastal Engineer, University of Southern California
• 
  Rosaly Lopes

  Self - Volcanologist, NASA-JPL
• 
  James Stephenson

  Self - NASA Astrobiologist, Univ. of Hawaii
• 
  Bill Sawyer

  Self - Speleologist, Caverns of Sonora