The Consequences of a Microbe-Free Earth: Biological, Ecological, and Societal Collapse

Which categories of organisms are eliminated in Professor Jack Gilbert's total microbial eradication thought experiment?

All bacteria, viruses, unicellular fungi, protozoa, and any biological entity existing solely as a single cell or particle.

Why would surgical procedures in non-sterile environments theoretically become safe if all microbes vanished?

Pathogenic bacteria, viruses, and infectious organisms would cease to exist, eliminating postoperative infections and the clinical need for antibiotics.

Why would humans suffer from severe malnutrition following microbial eradication despite consuming ample food?

The gut microbiome is essential for breaking down food matter and synthesizing vital metabolic compounds, chemicals, and vitamins.

How does the gut microbiome influence psychological conditions like depression and anxiety?

By maintaining endocrine hormone balance and regulating neurotransmitters synthesized in the brain.

Why is there no direct experimental data demonstrating how a completely germ-free human would behave?

Rearing a germ-free human in a laboratory setting is fundamentally unethical.

Why would terrestrial vegetation and agricultural crops turn brown and die without microbial life?

Plants depend directly on soil nutrients that are fixed, synthesized, and cycled by soil microbial communities.

Why do herbivorous livestock such as cattle and sheep starve when deprived of their resident gut bacteria?

They depend on symbiotic bacteria to digest cellulose in plant forage and extract metabolic energy.

What immediate impact does the halt of microbial nutrient cycling have on aquatic ecosystems?

Aquatic biomes collapse, leading to mass mortality events where dead fish cover the surfaces of lakes, rivers, and oceans.

How does the eradication of single-celled marine organisms impact planetary respiration?

Photosynthetic marine microbes produce a major portion of atmospheric $O_2$, causing atmospheric oxygen levels to plummet and inducing suffocation.

What planetary condition emerges within a few years of biological decomposition halting?

Organic decay ceases entirely, leaving the surface accumulated knee-deep in non-rotting animal carcasses and leaf litter.

Why would unpreserved carcasses remain non-poisonous to consume during famine in a microbe-free scenario?

The absence of putrefying and pathogenic bacteria keeps the non-decaying biological tissue sterile.

What are the two primary biological mechanisms that cause the extinction of all $7 \times 10^9$ humans in this scenario?

Starvation resulting from digestive and agricultural failure, and suffocation caused by atmospheric oxygen depletion.