Increasingly Earlier Life

Every creature inhabiting Earth, including newcomers like humans, represents an unbroken line to primitive carbon-based life present on Earth nearer and nearer to the planet's probable inception some 4.54 billion years ago.

Gnat encased in amber

"What we normally think of as 'life' is based on chains of carbon atoms, with a few other atoms, such as nitrogen or phosphorus."
— Stephen Hawking, from a 2008 lecture

Chains of carbon atoms are common to all living things.

Biogenic Substances

Biogenic substances contain carbon which is a recognized marker for living organisms. Such substances, in the form of constituents, or as secretions from plants or animals, embody biomolecules which are the building blocks of life.

coal & oil	geologic-age constituents that have undergone changes
chalk & limestone	geologic-age secretions (e.g., marine animal shells)
grass & wood	contemporary constituents
pearls, silk & ambergris	contemporary secretions

Improbable Life

That life-forming elements came from dying stars in the far reaches of the universe make life on Earth nearly incomprehensible, if not improbable.

I tell my students, with a feeling of pride that I hope they will share, that the carbon, nitrogen, and oxygen that make up ninety-nine per cent of our living substance were cooked in the deep interiors of earlier generations of dying stars. Gathered up from the ends of the universe, over billions of years, eventually they came to form, in part, the substance of our sun, its planets, and ourselves. Three billion years ago, life arose upon the earth. It is the only life in the solar system.
— George Wald, Harvard Biochemist ⁽¹⁾

olive-green zircon crystal
by Rob Lavinsky

Earliest Biogenic Substances

The earliest recorded biogenic substances on Earth gets incrementally pushed back as scientists find and analyze new artifacts.

Until recently, graphite detected in rock dated 3.8 billion years ago was the earliest known biogenic residue of life.

UCLA geochemists recently identified specks of biogenic carbon encased in undisturbed, crack-free zircon crystals from Western Australia.

This discovery pushes back the earliest biogenic residue some 300 millions years to 4.1 billion years ago. Thus it places the probable earliest life closer to the time when Earth was formed 4.54 billion years ago.

"Life on Earth may have started almost instantaneously. With the right ingredients, life seems to form very quickly."
— Mark Harrison, UCLA geochemist

REFERENCES

• 4.1 Billion Year Old Australian Zircon Contains Graphite of Biological Origin, Sci-News.com 20 October 2015.
• Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon, Elizabeth A. Bella, Patrick Boehnkea, T. Mark Harrison, and Wendy L. Maob, PNAS, 10.1073/pnas.1517557112, 14 October 2015.

⁽¹⁾ From speech given at an anti-war teach-in at the Massachusetts Institute of Technology, (4 Mar 1969) 'A Generation in Search of a Future', as edited by Ron Dorfman for Chicago Journalism Review, (May 1969)