Pre-midterm throwback
This scientist’s swan-neck flask experiment showed that microbes in the air, not “vital forces,” contaminate broth.
Who is Louis Pasteur?
These layered structures form when microbial mats trap sediment and slowly migrate upward toward the light.
What are stromatolites?
This potential complication to habitability is especially relevant for short-period planets in the habitable zones around M-dwarfs, where close-in orbits cause the same side of the planet to permanently face the star.
What is tidal locking?
Titan’s thick organic haze is produced when ultraviolet light drives photochemistry between these two major atmospheric gases, creating complex hydrocarbons that eventually settle onto the surface.
What are methane (CH4) and nitrogen (N2)?
Direct imaging of exoplanets requires this instrument to block out starlight and reveal the faint reflected light from orbiting planets.
What is a coronagraph?
In models of early Earth chemistry, this atmospheric molecule—produced efficiently by ultraviolet radiation—played a central role as a feedstock for prebiotic synthesis, generating nucleobases and amino acids in many laboratory simulations.
What is hydrogen cyanide (HCN)?
These tiny, extremely resistant crystals are used to infer Hadean conditions because they survive geological recycling and preserve ancient isotopic and trace-element information.
What are zircons?
On billion-year timescales, Earth’s climate is stabilized by this CO₂-removing process where carbonic acid reacts with silicate rocks and eventually stores carbon as carbonates.
What is the carbonate-silicate cycle?
This Viking experiment injected radiolabeled nutrients into Martian soil and measured the release of ¹⁴CO₂, giving a famously ambiguous “positive” result.
What is the Labeled Release Experiment?
This molecule is often used as an indirect biosignature or biosignature proxy, as it is easier to detect in the infrared than its biosignature counterpart.
What is o-zone (O3)?
In the Central Dogma of Molecular Biology, this process is the step where an RNA copy is made from a DNA template.
What is transcription?
A rock dominated by plagioclase feldspar and pyroxene is most likely this common volcanic rock found at Earth’s seafloor.
What is basalt?
This narrower subset of the habitable zone is defined as the range of distances where a planet can keep surface liquid water for most of the star’s lifetime, despite the star brightening over time.
What is the continuously habitable zone?
Mars’ classic river-valley networks date mostly to this earliest geological era, when surface conditions were warm and wet enough for sustained flow.
What is the Noachian?
In radio SETI, this nickname refers to the quiet frequency band between the hydrogen (H) and hydroxyl (OH) spectral lines — a symbolic “meeting place” where an intelligent civilization might choose to broadcast.
What is the water hole?
Because lipids have hydrophilic heads and hydrophobic tails, they spontaneously assemble into these structures that form the basis of cell boundaries.
What are membranes / lipid bilayers / vesicles?
A key requirement for microfossils to be accepted as biogenic is the presence of this in the fossil walls.
What is kerogen (organic carbon)?
This positive climate feedback involves melting ice reducing planetary reflectivity, leading to more warming and further melting.
What is the ice-albedo feedback?
Curiosity’s detection of seasonal methane at Gale Crater could come from modern methanogens, water-rock reactions, or release from these icy host structures — or all of the above.
What are methane clathrates?
False-positive biosignatures can arise when retrieval models are over-constrained. A major pitfall is allowing only a handful of gases in the model, which causes the inversion to misattribute spectral features to the wrong molecule. This mistake became particularly infamous in the debate over the detection of this compound on a nearby exoplanet.
What is DMS / DMDS?
Halophiles survive in extremely salty environments using one of two strategies: the “salt-in” strategy, which relies on specialized proteins that function at high ionic strength, and the “salt-out” strategy, which relies on accumulating these organic molecules that balance osmotic pressure without disrupting cellular function.
What are compatible solutes / amino acids and sugars?
Photosynthetic microbial mats promote CaCO₃ precipitation mainly by doing this to CO₂ in the water, shifting the carbonate equilibrium.
What is removing CO2 (via photosynthesis)?
This newer concept goes beyond habitability by asking whether an environment can actually support the origin of life — including feedstock molecules and processes like wet–dry cycles.
What is urability?
Enceladus’ global ocean was detected by measurements of this small but diagnostic “wobble.”
What is libration?
Many UAP videos of “insanely fast” objects are now explained by this geometric effect that makes slow, distant objects appear to streak by when viewed from a fast-moving aircraft.
What is motion parallax?