Privileged Planet: bacteria break down bedrock (Introduction)

by David Turell , Tuesday, December 17, 2019, 19:41 (1590 days ago) @ David Turell

The Earth started as a rocky planet, but to have life soil is needed. Bacteria were there first to start the job, and are still doing it:

https://www.sciencedaily.com/releases/2019/12/191216151447.htm

"Research published this week by University of Wisconsin-Madison scientists shows how bacteria can degrade solid bedrock, jump-starting a long process of alteration that creates the mineral portion of soil.

"Soil, which the aphorism describes as "that thin layer on the planet that stands between us and starvation," is a complex mishmash of minerals and organics.

"The problem is this, says senior author Eric Roden, a professor of geoscience at UW-Madison: "The general picture of soil shows solid bedrock a few meters below the surface, then a fractured, crumbly layer popularly called 'subsoil.' At the top is the rich, biologically active layer called soil. Chemical analysis links the minerals in soil to bedrock, but how does this extreme transformation take place?"

***

"Scientists have wondered for decades whether and how microorganisms could engage in the initial breakdown, but only now have they explained the essential trick that bacteria use to "eat" the upper surface of bedrock, says Roden.

"The process revolves around oxidation, familiar as the cause of rust in iron. Oxidation moves electrons, which supply energy to the bacteria, says Roden. "What we've developed is a picture of how bacteria slowly 'munch' rocks to extract energy without taking the minerals into their cells."

"In general, microbes ingest their "food" into their cells before they "eat" it, but they cannot ingest intact rock. So the diverse group of bacteria that Roden's group identified in the lab use proteins on their outer surface to move the electrons.

***

"...she inoculated the samples with material from the drill hole, which carried a natural stew of bacteria. She used a sterile fluid for her comparison samples.

After about two-and-a-half years in the dark, at room temperature, electron micrographs showed a radical change in surface texture -- but only if bacteria were present. "The rate of oxidation, weathering, was slow, but without the bacteria, it was zero," says Napieralski. "Although there is some chemical weathering in the critical zone, it was so slow that we did not see it during the experiment."

"'In my opinion, this type of metabolism has been going on basically forever, but unknown to us," says Roden. "This discovery opens up a whole other way of thinking about the oxidative weathering of ferrous silicate rock. We have danced around this for years. Rocks were dissolving, and microbes were involved. I kept saying, 'What about the microbial oxidation of rock?' and my colleagues said, 'Show me.'"

***

"Although the study focused on the dark, stable temperatures found at the top of bedrock, iron-oxidizing bacteria may also play a role in weathering higher up in the soil, Napieralski says. "External electron transfer is a way to cope with the difficulty of eating iron. One big thing in the paper is demonstrating that the organisms grew and coupled the oxidation of iron to the generation of ATP, the 'energy molecule' in all known types of life."

"A full understanding of life requires an accounting of energy, Roden says. "What we have found is that the cells make direct contact with an otherwise insoluble mineral, and they pull electrons from the mineral. They are getting energy from eating rock and along the way supplying nutrients for plants -- for life on Earth."

Comment: No wonder bacteria came first and are still here. They are the workhorses in evolution of a livable Earth as God's agents. Lichens do the job on the surface.