How did the building blocks of life first form on Earth?

Scientists investigate several lines of evidence. The Miller–Urey experiment showed amino acids can form from simple gases and an energy source like lightning. Communities around deep-sea black smokers show life’s chemistry could begin using chemical energy rather than sunlight. And organic molecules, including amino acids, have been found in meteorites, supporting the idea (panspermia) that building blocks could arrive from space. None is proven as the single answer, but together they show the building blocks can form in more than one way.

Where did the oxygen in Earth’s atmosphere come from?

From photosynthesis by cyanobacteria. These microbes released oxygen as a waste product; at first it was absorbed by dissolved iron (forming banded iron formations), but over hundreds of millions of years it built up in the air — the Great Oxidation Event around 2.4 billion years ago. Stromatolites, layered mounds built by microbial mats, are key evidence and still grow today at Shark Bay in Western Australia.

What were the Ediacaran and Cambrian, and why do they matter?

The Ediacaran fauna were the first large, soft-bodied, complex multicellular organisms, appearing a little over 540 million years ago and named after the Ediacara Hills in South Australia. The Cambrian explosion, around 541 million years ago, was a rapid burst in which most major animal body plans appeared — with shells, eyes and predators — transforming simple ecosystems into complex food webs.

How did life colonise the land?

Plants moved onto land first, more than 450 million years ago, evolving adaptations such as a waterproof cuticle, water-conducting vascular tissue and roots to avoid drying out and to stand against gravity. They built soil and changed the atmosphere. Animals followed — first invertebrates, then the vertebrate ancestors of land animals — having to solve drying out, supporting their weight in air, and breathing without gills.

The origin of the biosphere

Every living thing traces back to a moment when non-living chemistry first became life — and we can find evidence for each step, from a sparked jar of gas in the 1950s to 3-billion-year-old reefs still growing in Western Australia today. This powerbook follows that four-billion-year story: building blocks, the first cells, the air they made, complex life, and the conquest of land.

~4 bn

years of story

origin hypotheses

short sections

The origin of the biosphereSection 1 of 5

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This book has 5 short sections. Read each one, answer the check, then use Next to move on — the bar above tracks how far you've come.

From chemistry to the building blocks of life

Every living thing is built from organic molecules — carbon-based compounds like amino acids and sugars. So the first question about the origin of the biosphere is the hardest: on a young, lifeless Earth, how did these building blocks form at all, before there was any life to make them? Scientists cannot rerun four billion years, so they look for evidence of how it might have happened. Three lines stand out.

The first is a famous experiment. In the 1950s, Miller and Urey sealed water and a mix of simple gases thought to resemble the early atmosphere into glassware, and zapped it with electric sparks to mimic lightning. Within days, amino acids had formed — life’s building blocks, arising from nothing but simple chemicals and energy. (Later work suggests the early atmosphere may have differed from their mix, but organic molecules form under a range of plausible conditions, so the central lesson holds.)

The second line looks to the deep sea. Around black smokers — hot, mineral-rich hydrothermal vents — thrive communities that live by chemosynthesis, drawing energy from chemicals rather than sunlight. Such vents offer energy, minerals and shelter, making them a candidate cradle for life’s chemistry. The third looks to space: organic molecules, including amino acids, have been found inside meteorites — the idea that life’s ingredients, or even life itself, arrived from space is called panspermia. None of these is proven as the answer, but together they show that the building blocks of life can form in more than one way.

Simple gases plus a spark produced amino acids — life’s building blocks forming from non-living chemistry.

New words

organic molecules

Carbon-based molecules life is built from, like amino acids and sugars.

amino acids

The building blocks of proteins — shown to form without life in the Miller–Urey experiment.

panspermia/pan-SPUR-mee-uh/

The hypothesis that life or its building blocks arrived on Earth from space.

🔒 Lock it in

What did the Miller–Urey experiment demonstrate about the origin of life’s building blocks?

Answer the check to continue

Quick reference & sources

The interactive book above is the lesson. What follows is a plain recap you can revise from, plus the sources and how this maps to the syllabus.

Where the building blocks came from

Three lines of evidence for the origin of organic molecules: the Miller–Urey experiment (amino acids from sparked simple gases), communities around black smokers (life’s chemistry via chemosynthesis, without sunlight), and meteorites / panspermia (organic molecules from space). None is proven alone; together they show building blocks can form several ways.

Photosynthesis, oxygen and complex life

Cyanobacteria evolved oxygen-producing photosynthesis, slowly oxygenating the oceans (banded iron formations) then the air (the Great Oxidation Event, ~2.4 Ga); stromatolites record this and still grow at Shark Bay. Complex multicellular life came late: the soft-bodied Ediacaran fauna, then the Cambrian explosion (~541 Ma) of animal body plans.

The move onto land

Plants colonised land first (~470 Ma+), with adaptations like a waterproof cuticle, vascular tissue and roots to avoid drying out and stand up; they built soil and changed the air. Animals followed — invertebrates, then vertebrates — solving drying out, support and breathing air. The whole arc is read from experiments, living and fossil stromatolites, ancient rock chemistry and the fossil record.

For HSC students

This powerbook covers the Development of the Biosphere thread of Module 5 (Earth’s Processes), framed by the inquiry question how did today’s biosphere originate and develop? Working through it, you should be able to:

investigate evidence for the origin of organic molecules — the Miller–Urey experiments, communities around black smokers, and meteorites/panspermia;
investigate the evidence for photosynthetic life, including cyanobacteria and stromatolites;
evaluate the evidence for the origin of multicellular life and the resulting changes to ecosystems (Ediacaran and Cambrian fauna);
investigate the conquest of land by plants and animals.

The next chapter looks at how the developing biosphere reshaped the Earth’s geosphere, atmosphere and hydrosphere. Origin-of-life ideas are presented as scientific hypotheses with their evidence, including where that evidence remains uncertain. Explanations here are original and are a study aid, not a copy of the syllabus.

Sources

Miller & Urey (1953) and later origin-of-life research — abiotic formation of organic molecules.
Research on deep-sea hydrothermal vents (black smokers) and chemosynthetic communities; meteorite organics (e.g. the Murchison meteorite) and panspermia.
Geoscience Australia / published palaeobiology — cyanobacteria, stromatolites (including living examples at Shark Bay), and the Great Oxidation Event.
Palaeontological literature on the Ediacaran fauna (Ediacara Hills, South Australia), the Cambrian explosion, and the colonisation of land by plants and animals.
NSW NESA Earth and Environmental Science Stage 6 Syllabus (2017) — used only to scope the Module 5 content; explanations above are original.

Keep going

From a spark in a jar of gas to forests and animals: the biosphere is a four-billion-year chain of steps, each one written into rock we can still read — and each one setting up the next.