Everything Everywhere Daily

Episode: Challenger Deep and the Mariana Trench
Host: Gary Arndt
Date: October 27, 2025

Overview

In this episode, Gary Arndt dives deep into the mysteries of the Mariana Trench and its lowest point, Challenger Deep. The episode explores the trench’s geography, geological origins, record-breaking descents, mind-boggling physical conditions, endemic lifeforms, and the sobering presence of human pollution even in the most remote places on Earth. Arndt contextualizes Challenger Deep’s extremity, comparing its exploration with space missions, and highlights both the resilience of life and the impact of human activity at the planet’s greatest depths.

Key Discussion Points & Insights

1. Location, Scale, and Depth

• Mariana Trench Overview: Located south and east of Guam, forming an arc over 2,500 km (1,200 miles) long on the Pacific Ocean’s floor.
  (03:05)
• Challenger Deep: Not a single hole but three adjacent sub-basins at the trench’s southern end.
  (03:10)
• Depth Measurement: The deepest recent measurement is 10,935 meters (+/- 6 meters), or 35,876 feet. For context, this is about 6,000 feet deeper below sea level than Everest is above it.
  • “It is further below the sea level than the top of Mount Everest is above sea level by about 6,000 feet or 2,000 meters.” (03:45 – Host)
• Finding the True Deepest Point: Due to the trench’s size and irregularity, pinpointing the absolute lowest spot is challenging.

2. Geological Formation

• Subduction Zones: The trench was formed by the subduction of the Pacific Plate beneath the smaller Mariana Plate (part of the Philippine Sea Plate), moving at 2-3 inches per year.
  (04:25)
• Formation began about 50–60 million years ago (Eocene Epoch).
• The same geological process forms the volcanic Mariana Islands.

3. History of Exploration and Measurement

• Naming: “Challenger Deep is named after the HMS Challenger, a British Royal Navy survey ship that conducted the first systematic study of the world's oceans from 1872 to 1876.” (05:20 – Host)
• First Survey (1875): HMS Challenger measured depths with weighted lines — approximately 8,184 meters (26,850 feet), far shallower than later, more accurate measurements.
• Next Measurements:
  • 1951: HMS Challenger 2 — echo sounding, 10,863 m (35,640 ft).
  • 1957: Soviet vessel Vityaz — 11,034 m (36,201 ft), but likely an overestimation.

4. Manned Misions to Challenger Deep

• Trieste Dive (1960): Jacques Piccard and Don Walsh descended in the Bathyscaphe Trieste.

  • Vessel Details: Seven-foot-wide steel sphere, five-inch-thick walls for protection against pressure, gasoline float for buoyancy, and iron pellet ballast.

• Duration: 4 hours 48 minutes to descend, 20 minutes at the bottom, 3 hours 15 minutes to ascend.

• Pressure: “It's approximately 1,100 atmospheres, or about 16,000 pounds of pressure per square inch. It would be the equivalent weight of the entire Empire State Building being put on an area the size of your foot.” (07:25 – Host)

• Subsequent Visits:

  • 2012: James Cameron in Deepsea Challenger, spent three hours at the bottom.
  • 2019: Victor Vescovo — third ever dive, now completed 15 descents.
  • Other notables: Astronaut Kathryn Sullivan (2020); game designer Richard Garriott (2021).
  • As of episode, 27 total people have visited Challenger Deep versus 24 who have landed on or orbited the moon.

  “More people have been to space than have visited the bottom of the sea… In many respects, going into space is actually easier.” (06:25 – Host)

5. Conditions at the Bottom

• Environment: The Hadal Zone (from the Greek 'Hades')
  • “There's a whole lot of nothing. People who have been there have described it as being like on an enormous salt flat. It's mostly sediment with few recognizable features.” (09:18 – Host)
  • No light penetrates beyond 300 meters — Challenger Deep is in perpetual darkness.
  • Temperatures hover just above freezing (34°F, 1°C).
  • Water at this depth is isolated, “the oldest in the world's oceans because it's the endpoint of the conveyor belt… water in Challenger Deep may be 2,000 years old or more before being replaced.”
• Seawater Density and Physics: Water compresses slightly (~4-5% denser than surface water).
  • Speed of sound is higher: 1500-1550 m/s at depth.

6. Life at Challenger Deep

• Despite the darkness and crushing pressure, life persists.
• Microbes: Pressure-loving 'piezophiles' that metabolize sulfur, methane, nitrogen, and form the deep food chain’s base.
• Multicellular life: Amphipods (shrimp-like), nematodes, and sea cucumbers found. No vertebrates have been observed here.

  “One thing that has never been observed at Challenger Deep are fish or other vertebrates… It's likely because cellular membranes and enzymes can't function properly beyond about 8,400 or 8,600 meters.” (11:30 – Host)

7. Human Impact: Pollution at the Deepest Point

• Early explorations found only sediments and a few creatures (1960).

• Recent dives (2019–2021):

  • Plastic bags, food wrappers, and microplastics found at nearly 10,900 meters.
  • Amphipods carried persistent organic pollutants.

  “In 2019… Victor Vescovo filmed what appeared to be a plastic bag… Later, dives found other fragments of plastic and fabric mixed into the sediment.” (12:30 – Host)

  • “Even from the most remote part of the trench… laboratory analysis… revealed that their bodies contained traces of persistent organic pollutants, some of which had been banned decades ago.” (13:00 – Host)

• Because water movement is minimal, pollution can remain at Challenger Deep for thousands of years.

Notable Quotes & Memorable Moments

On Depth Comparison

• “It is further below the sea level than the top of Mount Everest is above sea level by about 6,000ft or 2,000 meters.”
  — Gary Arndt (03:45)

On the Difficulty of Deep-Sea vs. Space Travel

• “In many respects, going into space is actually easier. … From a pressure standpoint, being in space is actually much easier. Once pressure gets down to zero, that's it. However, pressure can theoretically keep increasing until you reach a black hole.”
  — Gary Arndt (06:26)

On the Experience at the Bottom

• “People who have been there have described it as being like on an enormous salt flat. It's mostly sediment with few recognizable features... It's also totally dark.”
  — Gary Arndt (09:18)

On Life's Limits

• “The deepest known fish, the Haddle snailfish, lives on the trench slopes up to about 8,200 meters, but no deeper. It's likely because cellular membranes and enzymes can't function properly beyond about 8,400 or 8,600 meters.”
  — Gary Arndt (11:30)

On Pollution Reaching the Deepest Point

• “In 2019… Victor Vescovo filmed what appeared to be a plastic bag and several candy or food wrappers lying on the seafloor at nearly 10,900 meters… laboratory analysis of amphipods collected from Challenger Deep revealed that their bodies contained traces of persistent organic pollutants, some of which had been banned decades ago.”
  — Gary Arndt (12:30–13:10)

Timestamps for Key Segments

• 03:03 — Defining the Mariana Trench and Challenger Deep; measurements of depth
• 04:25 — Geological origins and ongoing subduction
• 05:20 — Naming and HMS Challenger’s early soundings
• 06:00 — Technological advances in measuring depth; the challenge in finding the lowest point
• 06:26 — Comparison of deep-sea vs. space exploration
• 07:15 — Details of the 1960 Trieste descent
• 09:00 — Environmental conditions in Challenger Deep (light, temperature, pressure)
• 10:15 — Physical behavior of water at these depths
• 11:00 — Life forms in the Hadal Zone
• 12:30 — Discovery of human pollution at Challenger Deep

Conclusion

This enlightening episode highlights the astonishing natural wonder that is the Mariana Trench, the intense effort required to study and reach Challenger Deep, and the unfortunate reality that even the most inaccessible environments on Earth are not immune to human impact. Gary Arndt's approachable, fact-rich storytelling makes complex oceanography and exploration history easy to grasp—reminding us of both the resilience of Earth's life forms and the persistence of our footprint on the planet.

Final notable quote:
“Challenger Deep is the most extreme environment on planet Earth. It's extremely difficult to get to, and once you're there, you can't stay very long. Yet, despite being so inhospitable, life manages to find a way. Life and Garbage.”
— Gary Arndt (13:30)