The orbital spacecrafts, landers, and rovers sent to Mars under NASA's Mars Exploration Program (MEP) have provided invaluable insights into the red planet's topography, climate, and natural resources. However, finding any evidence of life has proved elusive. Now, the discovery of microbial growth found inside ancient, cold oceanic crust in the middle of the South Pacific is giving scientists hope that the proof may already be with us — we just need to know where to look!
The chain of events leading to the unexpected discovery began in 2010, when Yohey Suzuki, an associate professor at the University of Tokyo, joined a team of researchers on the Integrated Ocean Drilling Program (IODP). The research ship, which took the scientists from the tropical island of Tahiti in the middle of the South Pacific Ocean to Auckland, New Zealand, anchored at three locations to collect mud and rock samples from the Earth's core — about 410 feet (125 meters) below the seafloor. Depending on the location, the specimens were estimated to be 13.5 million, 33.5 million, and 104 million years old.
To prevent surface contamination, the samples were first sterilized using an artificial seawater wash and a quick burn. Then began the tedious search for microbes. At that time, the usual process to discover bacteria in rock samples was to strip the rock's outer layer, grind its center into a powder, and count cells from the crushed stone. "I was making loud noises with my hammer and chisel, breaking open rocks while everyone else was working quietly with their mud," Suzuki recalls. Unfortunately, the researcher found no evidence of bacteria.
Convinced the ancient rocks harbored life, Suzuki has since been seeking a better way to find evidence. He recently came up with the idea of slicing the rock samples, similar to how pathologists prepare ultra-thin slices of body tissue samples to diagnose illnesses. To ensure the specimens would not crumble when sliced, Suzuki first coated them with a special epoxy. The thin rock layers were then washed with DNA staining dye and placed under a microscope. Sure enough, a large number of bacteria, which appeared as glowing green spheres, were clustered inside tunnels of clay mineral deposits that glowed orange. The excited researcher says, "I thought it was a dream, seeing such rich microbial life in rocks."
DNA analysis revealed that while the species of bacteria from each location were similar, they were not identical. Suzuki and his colleagues estimate that the cracks, measuring about one millimeter in width, housed as many as 10 billion bacterial cells per cubic centimeter. In comparison, the clay samples extracted from the ocean floor have only about 100 bacterial cells per cubic centimeter. The team speculates the clay mineral-filled cracks contain a large concentration of nutrients upon which the bacteria sustain themselves.
The discovery of organisms in the ancient iron-and-clay-rich rocks is particularly exciting since the environment is similar to that found on Mars. Like Earth's, the red planet's crust was formed nearly four billion years ago from lava that erupted and rapidly cooled and hardened. Though the lakes and other bodies of water that once existed have dried up, they left behind craters of mineral-rich clay, similar to the clay found underneath the Earth's seafloor.
Suzuki says, "Minerals are like a fingerprint for what conditions were present when the clay formed. Neutral to slightly alkaline levels, low temperature, moderate salinity, iron-rich environment, basalt rock — all of these conditions are shared between the deep ocean and the surface of Mars."
The team, who published the findings in the journal Communications Biology on April 2, 2020, is now collaborating with NASA's Johnson Space Center to devise a plan to examine the Martian surface rocks collected by the rovers. A thrilled Suzuki asserts, "This discovery of life where no one expected it in solid rock below the seafloor may be changing the game for the search for life in space."
Will we finally find evidence of aliens on Mars? Stay tuned!
Resources: www.u-tokyo.ac.jp, CNN.com