Physics, Earth & Space Icon Physics, Earth & Space

Much Ado About Martian Organics

Casey Luskin


The news from NASA today, undeniably of some mild interest, is being overblown. If extraordinary claims require extraordinary evidence, that bar has most certainly not been met here.

From USA Today:

NASA Curiosity Rover unearths building blocks in 3-billion-year-old organic matter on Mars

The “building blocks” for life have been discovered in 3-billion-year-old organic matter on Mars, NASA scientists announced Thursday.

Researchers cannot yet say whether their discovery stems from life or a more mundane geological process.  However, “we’re in a really good position to move forward looking for signs of life,” said Jennifer Eigenbrode, a NASA biogeochemist and lead author of a study published Thursday in the peer-reviewed journal Science.

The findings were also remarkable in that they showed that organic material can be preserved for billions of years on the harsh Martian surface.

First of all, life’s “building blocks” would imply something like amino acids or nucleotides. What they found are organic molecules but not something in a molecular form that is important for life. So that’s one problem.

An Ambiguous Term

What’s more, organic doesn’t necessarily mean biological. The term “organic” is ambiguous — we often take it to mean “life-related” but it doesn’t have to mean that. Organic entails “containing carbon,” as this NASA video says, but organic molecules can have biological or non-biological origins.

Inorganic carbon is carbon that is found in compounds that are completely unlike biological molecules. “Organic” carbon can mean biologically derived, but it can also have nonbiological sources. The Wikipedia article on “organic matter“ makes the point: “Organic molecules can also be made by chemical reactions that don’t involve life.”

Some geologists devote their careers to seeking organic inclusions in Earth rocks, hoping to find ancient fossils of terrestrial life. One of their most difficult tasks is to prove that the carbon they find is biogenic, and not produced through non-living, geological processes. It’s very tricky — and this is on Earth where there are vast quantities of biogenic carbon.

So now they want people to think that finding a few organic molecules on Mars is an advance toward finding evidence of past life? Oh, please — even on Earth what they found would not be enough to support the claim! On Mars, where we only have a few molecules from a remote probe, this stuff is light years away from being conclusive.

So What Did They Find?

Here’s what the news article at Science said:

The team picked up a welter of closely related organic signals reflecting dozens or hundreds of types of small carbon molecules, probably short rings and strands called aromatics and aliphatics, respectively. Only a few of the organic molecules, sulfur-bearing carbon rings called thiophenes, were abundant enough to be detected directly, Eigenbrode says.

That’s a long way from finding, say, amino acids or nucleotides. In fact, thiophenes are pretty simple molecules that are just a 5-sided carbon ring, but with a sulfur molecule replacing a carbon atom. See the Wikipedia article on thiophene.

These may be “organic” in that they include carbon, but we’re not aware of these being precursors to anything biological. Moreover, sulfur is a very common element in geological minerals, so it’s not at all surprising to find it in some non-biological carbon deposit.

Geological, or Biological?

In fact, Science admits that there are easy ways to explain this without appealing to biology:

It’s impossible to say whether ancient life explains the Martian organics, however. Carbon-rich meteorites contain kerogen-like compounds, and constantly rain down on Mars. Or reactions driven by Mars’s ancient volcanoes could have formed the compounds from primordial carbon dioxide.

That’s why one of the scientists they quote says, “I suspect it’s geological. I hope it’s biological.” “Hope,” it seems, rather than objectivity is what’s driving this story.

Photo: Curiosity Rover, by NASA/JPL-Caltech/MSSS.