Where did this well known symbol come from?

In order to further explore a cave in San Antonio, Rob Nelson crawls through incredible tight caverns. Don’t worry though, he’s only a little claustrophobic.

There’s a mysterious underwater rock circle that supposedly has carvings in it.

Rob's gear malfunctioned underwater.

Go with Rob behind the scenes to see where parts of the show are shot!

Gungywamp was one of Rob’s favorite spots during this season of Secrets of the Underground!

The Great Serpent Mound is a 1,348-foot-long prehistoric effigy mound in Ohio. Scientists are sure what it’s purpose was.

A collection of dinosaur marks can be found near Denver. Some of these markings are believed to be part of a mating ritual that can still be seen in modern bird species.

Enormous dinosaurs and teeny birds have a lot more in common than you might think!

First, scientists like to date the rock in which the fossil is on. Radiometric dating is a technique used to date materials such as rocks or carbon.

What is Pi and where did its symbol come from?

The cave in central Texas is home to more than 10,000 prehistoric fossils.

A single bill contains dozes of symbols.

The official reports claim that all 57 workers died from Cholera, but something more sinister may have occurred.

Funny enough, these symbols were used to classify plants before classifying humans and animals.

In this digital exclusive, Rob Nelson shares extra details about his time spent in this cave full of prehistoric fossils.

They’re very, very tiny simulations that allow scientists to learn more about the physics of earthquakes.

On the Oregon coast there is a natural hole that appears to drain the sea.

Rob loved exploring Thor's Well despite how dangerous and difficult it was.

In order to see fine details underwater, scientists use special tech.

Over the past five thousand years, shorelines have been completely reworked.

Supervolcanoes occur when magma in the mantle rises into the crust but is unable to break through it and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure.

Near Fresno, California, there are alarming signs of possible volcanic activity.

Out of all the places that Rob visited during the filming of Secrets of the Underground, which one does he think people should definitely visit?

Rob Nelson and the Secrets of the Underground crew stayed after hours to capture footage at this infamous prison.

Gungywamp was one of Rob’s favorite spots during this season of Secrets of the Underground!

Secrets of the underground premieres on Valentine's Day!

Get ready for the new Science Channel series, Hacking the Wild!

Using just a simple hand drill and a large stick, Andy was able to make a clothes dryer!

You get start a fire using the acidity from a pineapple!

Andy needs fresh water, so he looks to a laptop screen and old snail shells to help him fight dehydration.

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