1. How Researchers Discovered Lost City on the Atlantic Seafloor in 2000
Lost City was discovered in December 2000. It was found during a research voyage in the central Atlantic, supported by the U.S. National Science Foundation. The researchers were not looking for this specific site; it was a chance discovery. [2] The name "Lost City" means "the lost town."
The largest tower is named Poseidon. It is about 60 meters high, though some sources say it is more than 60 meters. Researchers compared it to an 18-story building. [2] [4] The entire area covers about 90 by 300 meters (300 by 1,000 feet). It contains about 30 large towers that range from 9 to 55 meters (30 to 180 feet) tall. [2]
The site is located on the Atlantis Massif, a seamount at 30 degrees North latitude, near the Mid-Atlantic Ridge. Here, rocks from deep inside the Earth (the mantle) are exposed on the seafloor. [5] However, there are no volcanoes nearby. So, where does the heat that warms the water come from?
2. How Seawater Reacting with Mantle Rock Produces Heat
The source of the heat is a chemical reaction called serpentinization. This happens when seawater reacts with mantle rocks, specifically peridotite. [1] When seawater soaks into the exposed peridotite on the seafloor, the rock changes properties, and heat is released in the process. [5]
This is different from black smokers, which are heated by volcanic magma. A helpful comparison is to the heat of rusting iron, like in a disposable hand warmer. However, the rocks and reactions involved are completely different. [1]
In addition to heat, this reaction produces gases like hydrogen and methane. As we will see later, these gases become food for microbes. [1] How does the water from this process differ from the water at black smokers?
3. How Lost City Differs from Black Smokers in Temperature and Chemistry
At black smokers, the water that shoots out can reach about 400°C. The water is acidic and contains iron and sulfur, creating chimneys made of sulfides. [1]
In contrast, the water at Lost City is about 40 to 90°C. It is strongly alkaline, with a pH of 9 to 11. [3] pH measures acidity or alkalinity; 7 is neutral, and higher numbers mean more alkaline. If you compare the highest temperatures, the 400°C at black smokers is about 310°C hotter than the 90°C at Lost City. The towers at Lost City are made of nearly pure carbonate, similar to cave limestone, not sulfide chimneys. [1] [2]
The activity also lasts longer. Radiocarbon dating suggests the towers have been active for at least about 30,000 years. This is much longer than the lifespan of black smoker chimneys. [9] The age estimates vary depending on the study. It is relatively cool, alkaline, and white—opposite to black smokers. What lives here?
4. How Lost City Microbes Get Energy from Hydrogen and Methane
The microbes at Lost City seem to use abundant methane and hydrogen as their energy source. [2] At black smokers, carbon dioxide becomes an important carbon source, but the fluid at Lost City has very little of it. [2]
Hydrogen and methane are created by the serpentinization reaction. Compared to typical black smoker systems, Lost City produces 10 to 100 times more hydrogen and methane. It also creates more complex hydrocarbons. [1]
Famous creatures from black smokers, like tube worms and shrimp, have not been found here. The diversity of microbial types is also not very high. [2] In hot, active chimneys, archaea thought to be close to methane-producing bacteria (Methanosarcinales) are common. In cooled chimneys, archaea called ANME-1, which break down methane, are found. [3] Whether these bacteria produce or break down methane is not yet settled. The reaction between rock and seawater provides both heat and food. Does this relate to the beginning of life?
Safety Note: The supply of hydrogen and methane is supported by scientific evidence.
5. Whether Lost City Could Show How Life Began
Because hydrogen, methane, and hydrocarbons are created just by the reaction of rock and seawater, hydrothermal fields like Lost City are written about as a "leading candidate for the place where life began." [1] It is a candidate, not a confirmed fact that life started here.
There is another reason for this hypothesis. It is estimated that the ancient ocean was weakly acidic. When this acidic water met alkaline hydrothermal water, the difference in pH might have created energy. This is similar to how a difference in water height in a dam turns a water wheel. [1]
However, in 2016, Jackson argued that there is no evidence yet that thin mineral membranes at Lost City maintain a sharp pH difference. He suggested that natural pH gradients likely did not play a role in the origin of life. [7] The pH of the ancient ocean is an estimate, not a measurement. There are points supporting the hypothesis and points criticizing it. No conclusion has been reached. What are researchers doing to find out?
6. How Scientists Drilled the Seafloor in 2023 to Study Rocks
In 2023, during Expedition 399 of the International Ocean Discovery Program (IODP), researchers used the research vessel JOIDES Resolution to drill into the Atlantis Massif. The goal was to investigate where and how hydrogen and methane are made, and how they reach the hydrothermal fluid. [5]
They recovered 1,268 meters of serpentinized mantle rock. The pattern of changes in the rock matched the composition of the hydrothermal fluid at nearby Lost City. [6] The drilling site was about 800 meters north of Lost City, and there are no volcanoes nearby. [8]
Also, an existing borehole (U1309D) is 1,415 meters below the seafloor, with a bottom temperature of 140°C. This temperature exceeds the limit for microbial life. Therefore, it is expected that any hydrogen, methane, or organic matter made deeper down is created by reactions alone, not by living things. [5]
However, the results only "support" the idea. The possibility of seawater mixing in has not been ruled out. It has not been definitively shown that the underground hole and the towers at Lost City are connected by a single path. [8]
7. How to Test Carbonate, the Tower Material, at Home
The material of the towers at Lost City is carbonate. Shells and eggshells are also members of the carbonate family, so you can check their properties at home. [1]
Try this: Place a washed and dried eggshell or shell on a small dish and add a little vinegar. If small bubbles appear, it shows the property of carbonate. Do this with an adult to keep vinegar out of your eyes, and do not eat the shells after using them. Note that the towers and shells may not have the exact same composition, but this is an entry point to understanding carbonate properties.
Another activity: Use an atlas to trace the line of 30 degrees North latitude and look for the middle of the Atlantic Ocean. Near the ridge is where Lost City is located. [5]
The next question extends beyond Earth. The commentary on IODP Expedition 399 states that similar systems using serpentine reactions might exist on icy moons like Saturn’s moon Enceladus. [5] This is a suggestion of possibility, not a confirmed fact that they exist there.