The ancient Martian meteorite ALH84001 (pictured) was discovered in Antarctica in 1984. It contains organic molecules that researchers now think were formed by geologic processes, not by alien life.
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February 9, 2022 at 6:30 am
A chunk of Mars that had landed in Antarctica caused quite a stir in 1996. Scientists reported that this meteorite contained organic compounds. Such carbon-based molecules are the building blocks for life. Some researchers thought these organics were evidence of life on Mars. Others were not convinced. Now, a closer look at the meteorite lends more support to those skeptics.
Some had argued that earthly life could have contaminated the rock. Others suggested some process on Mars not involving life might also have created the organics. The new study suggests this rock’s organics formed through water and minerals mingling at or under Mars’ surface.
Researchers shared that finding in the January 14 Science.
But it’s not all bad news for alien enthusiasts. The meteorite, known as ALH84001, could still aid in the search for life. How? Organic molecules produced by non-living things are thought to be necessary to spark life. “These organic chemicals could have become the primordial soup that might have helped form life on [Mars],” says Andrew Steele. Whether life ever existed there, though, remains unknown.
Steele is a biochemist. He works at the Carnegie Institution for Science. It’s in Washington, D.C. Steele was part of a team that set out to study how Martian water may have triggered a morphing of minerals in ALH84001. The team used microscopes and other tools to view tiny slivers of the meteorite. They focused on parts that appeared to have reacted with water.
These samples contained by-products of two chemical reactions. One is called serpentinization (Sur-pen-tin-ih-ZY-shun). The other is carbonation. Both can occur as fluids interact with minerals, changing them. Amid by-products of these reactions the researchers found complex organic molecules. That led the team to conclude the organics probably formed during such reactions on Mars. The same thing happens on Earth.
The types of hydrogen in ALH84001’s organic matter also offered clues to its origins. The hydrogen helped confirm that the organic compounds formed on Mars. The molecules did not emerge later from microbes on Earth. They also were not created by materials in the researchers’ lab.
It seems that at least two geologic processes on Mars made the organic matter in ALH84001, says Mukul Sharma. He’s a geochemist who did not take part in the new study. He works at Dartmouth College in Hanover, N.H.
ALH84001 is about 4 billion years old. That makes it one of the oldest Martian meteorites ever found. Other, younger bits of the Red Planet also contain complex organics. These molecules, too, are thought to have come from interactions between water and rock. So geology may have been making organic material across Mars for much of its history. “Nature has had a huge amount of time on its hands to produce this stuff,” Sharma says.
This study doesn’t prove or disprove the existence of life on Mars. But finding non-living sources of organics there is crucial for the search, Steele says. Scientists must first figure out how Martian organic chemistry works without life. After that, he says, “you can then look to see if it’s been tweaked.” Such tweaks would offer real evidence of Red Planet life.
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alien: A non-native organism. (in astronomy) Life on or from a distant world.
Antarctica: A continent mostly covered in ice, which sits in the southernmost part of the world.
carbonation: The process of pumping carbon dioxide into a liquid, to imbue that liquid with bubbles. It gives the now- carbonated liquid a fizzy taste.
chemical: A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.
chemical reaction: A process that involves the rearrangement of the molecules or structure of a substance, as opposed to a change in physical form (as from a solid to a gas).
chemistry: The field of science that deals with the composition, structure and properties of substances and how they interact. Scientists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances.
compound: (often used as a synonym for chemical) A compound is a substance formed when two or more chemical elements unite (bond) in fixed proportions. For example, water is a compound made of two hydrogen atoms bonded to one oxygen atom. Its chemical symbol is H2O.
geologic: An adjective that refers to things that are related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.
geology: The study of Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists. Planetary geology is the science of studying the same things about other planets.
hydrogen: The lightest element in the universe. As a gas, it is colorless, odorless and highly flammable. It’s an integral part of many fuels, fats and chemicals that make up living tissues. It’s made of a single proton (which serves as its nucleus) orbited by a single electron.
Mars: The fourth planet from the sun, just one planet out from Earth. Like Earth, it has seasons and moisture. But its diameter is only about half as big as Earth’s.
meteorite: A lump of rock or metal from space that passes through Earth’s atmosphere and collides with the ground.
microbe: Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.
microscope: An instrument used to view objects, like bacteria, or the single cells of plants or animals, that are too small to be visible to the unaided eye.
mineral: Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns).
molecule: An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).
organic: (in chemistry) An adjective that indicates something is carbon-containing; also a term that relates to the basic chemicals that make up living organisms. (in agriculture) Farm products grown without the use of non-natural and potentially toxic chemicals, such as pesticides.
planet: A large celestial object that orbits a star but unlike a star does not generate any visible light.
primordial: An adjective that refers to something that goes back to the beginning of time or to the earliest existence of something.
Red Planet: A nickname for Mars.
skeptical: (n. skeptic) Not easily convinced; having doubts or reservations.
tool: An object that a person or other animal makes or obtains and then uses to carry out some purpose such as reaching food, defending itself or grooming.
Journal: A. Steele et al. Organic synthesis associated with serpentinization and carbonation on early Mars. Science. Vol. 375, January 14, 2022, p. 172. doi: 10.1126/science.abg7905.
Nikk Ogasa is a staff writer who focuses on the physical sciences for Science News. He has a master’s degree in geology from McGill University, and a master’s degree in science communication from the University of California, Santa Cruz.
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No, organic molecules alone don't point to life on Mars – Science News for Students
