Free HSC Earth and Environmental Science Flashcard Review

Methane, ammonia, hydrogen and water vapour, a reducing mixture with no free oxygen. Electric sparks modelled lightning as the energy source.

Amino acids and other simple organic molecules formed from inorganic gases without life. It showed that the building blocks of life could form abiotically on the early Earth.

The early atmosphere is now thought to have been less reducing (mainly CO₂, N₂ and water vapour), which gives much lower yields; it also made only small molecules, not self-replicating systems.

A hydrothermal vent on a mid-ocean ridge where superheated, mineral-rich water (above 350 °C) gushes out and precipitates black metal sulfides, building chimneys.

The production of organic compounds by microbes using energy from oxidising inorganic chemicals such as hydrogen sulfide, instead of sunlight.

They support complex food webs without sunlight, based on chemosynthetic microbes, and vents supply energy, reduced chemicals and mineral surfaces, so life could have begun in similar settings.

The hypothesis that life or its organic building blocks arrived on Earth from space, for example on meteorites or comets.

Dozens of amino acids and other organic compounds of extraterrestrial origin, showing that organic molecules form in space and could have been delivered to the early Earth.

It moves the origin of life somewhere else rather than explaining it, and organic molecules in meteorites are not living organisms.

Prokaryotic microorganisms that carry out oxygenic photosynthesis, releasing O₂. They were the first organisms to oxygenate Earth's atmosphere and oceans.

A layered sedimentary structure built by microbial mats (mainly cyanobacteria) that trap and bind sediment and precipitate carbonate, growing upward towards light.

In the Pilbara region of Western Australia, about 3.5 billion years old (e.g. the Dresser and Strelley Pool formations).

Modern stromatolites are built by photosynthetic cyanobacteria, so ancient stromatolites with the same structure are inferred to have formed the same way.

The first sustained rise of free oxygen in the atmosphere, about 2.4–2.3 billion years ago, after oxygen from cyanobacteria exceeded what iron and other sinks could absorb.

A sedimentary rock of alternating iron-oxide-rich bands (haematite, magnetite) and silica-rich chert bands, mostly deposited 2.5–1.8 billion years ago.

Oxygen from photosynthesis oxidised dissolved ferrous iron in seawater to insoluble ferric oxides, which precipitated on the sea floor in layers.

They are the source of most of Australia's iron ore exports from the Pilbara, WA.

Terrestrial sedimentary rocks coloured red by iron oxides. They appear after about 2 billion years ago and indicate oxygen in the atmosphere.

It produced BIFs and red beds, built stromatolite carbonates and stopped the accumulation of easily oxidised minerals such as detrital pyrite and uraninite in sediments.

The oldest widely accepted large multicellular organisms (about 575–541 Ma), mostly soft-bodied, named after the Ediacara Hills in the Flinders Ranges, South Australia.