Today’s journey marks Wade’s ninth visit to Clearwater Cave, the longest underground passage in all of Southeast Asia and one of only four Mula caves open to the public. The geologist leans back from his seat in the longboat, shining his carbide light at the alabaster ceiling of the cavern. The beacon cuts through the darkness to reveal a myriad of stalactites dripping with moisture. Wade stares at the ancient formations of rock, marveling at Nature’s design.

Four billion years ago, the Earth was a very young, hostile, and lifeless world. As the planet cooled, water vapor and other gases were sent skyward in violent volcanic eruptions, creating an atmosphere high in carbon dioxide, nitrogen, and hydrogen compounds, conditions similar to those found on Venus.

Life on our planet began in the sea as a soup of chemicals, organized into complex structures—four basic amino acid chain molecules—animated by an outside catalyst, perhaps a bolt of lightning. The animated amino acid double helixes began to replicate themselves, leading to a single-celled life. These organisms quickly rose in abundance and began depleting the oceans of its fast-food carbon compounds. Then a unique family of bacteria evolved to produce a new organic molecule called chlorophyll. This green-tinted substance was able to store the energy in sunlight, allowing the single-celled organisms to create high-quality carbohydrates from carbon dioxide and hydrogen, releasing oxygen as its by-product.

Photosynthesis was born.

As planetary oxygen levels rose, calcium carbonate was withdrawn from the sea and locked up in rock formations by marine organisms, drastically reducing the planet’s atmospheric levels of carbon dioxide. This rock-limestone became Earth’s storehouse for carbon dioxide. As a result, the level of carbon dioxide stored in sedimentary rock is now more than six hundred times the total carbon content of the planet’s air, water, and living cells combined.

Wade Tokumine aims the beam of light along the dark surface waters of the cavern. The subterranean stream is laden with ten times the concentration of carbon dioxide. This part of the carbon cycle occurs as a result of the dissolved CO2 reaching its saturation point within the limestone. When this happens, the carbon dioxide precipitates out as pure calcium carbonate, creating the stalactites and stalagmites that now proliferate in the Sarawak caves.

Wade turns around in the longboat to face his guide, Andrew Chan. The Malaysian native and professional spelunker has been leading tours through Sarawak’s caves for seventeen years.

“Andrew, how much farther to this virgin passage of yours?”

The light of the carbide lamp catches Andrew’s smile, which is missing two front teeth. “Not far. This section of the cavern craps out ahead, then we go on by foot.”