(12) How did life begin?

How did living organisms evolve on Earth from simple molecules and ions?

To me, personally, this is the greatest of scientific mysteries yet to be solved.

Despite all the fossil and genetic evidence of evolution, there is no clear answer as to how it all began!

Current evidence suggests that life on Earth began about ~3.7 billion years ago (~3.7x 10⁹ years).

One of the earliest forms of life we have evidence for is a relative simpler cyanobacteria.

It is even possible one of these simple forms of life evolved into photosynthesising blue-green algae from as far back as ~3 billion years ago  (~3 x 10⁹ years) - amazing the power of sunlight could be harnessed so early in plant Earth's story !!!

There are various hypotheses to suggest how some simple form of self-replicating life evolved, but that is what they are - just hypotheses!

Did life evolve in some kind of pool of simple/complex organic molecules and mineral salts?

Did the molecules of life arrive on a comet?

Did the water, the medium in which life is considered tom have evolved, arrive in massive icy comets?

Could life have evolved by hot volcanic springs under the sea where simple extremophile organism still exist?

The first problem is lack of evidence of the structure and function of early forms of life.

There are two principal reasons for this.

(i) The earliest fossil records are not clear, especially as early forms of life would have tiny soft bodies that would readily decay leaving little if any trace of the organism's existence.

(ii) Many fossils formed millions of years ago have been destroyed by the Earth's geological activity e.g. tectonic plate movements crushing and disrupting layers of sedimentary rock, volcanic activity, and the weathering and erosion of the earliest rocks - the latter means that much of the earliest layers of sedimentary rock containing many of the earliest fossils has disappeared.

I've written a wider discussion from more of a pure chemistry point of view on my webpage

Evolution and the Earth's atmosphere

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Key points Based on the syllabus-specifications for students taking the AQA, Edexcel and OCR GCSE level biology examinations (~US grades 9-10).

Summary of current key ideas on the origin of life

The Origin of Life on Earth

Scientists believe life on Earth originated around 3.5 to 4 billion years ago through a combination of chemical processes and environmental factors.

Although the exact details remain unknown, multiple scientific theories provide insights into how life may have begun, but no theory has proved satisfactory, it is a great mystery!.

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1. Early Conditions on Earth

• The early Earth was hot, volcanic, and rich in gases like methane, ammonia, water vapor, and carbon dioxide.

• There was no oxygen in the atmosphere, and conditions favoured complex chemical reactions.

• The presence of oceans, energy sources (lightning, volcanic activity, UV radiation) helped form simple organic molecules.

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2. Theories of the Origin of Life

A. The Primordial Soup Hypothesis

• Suggested by Oparin and Haldane in the 1920s.

• The early oceans contained simple organic molecules, forming a "chemical soup."

• Energy from lightning or radiation triggered chemical reactions, leading to the formation of amino acids (building blocks of proteins).

• Supported by the Miller-Urey experiment (1953), which recreated early Earth conditions and produced amino acids.

B. Deep-Sea Hydrothermal Vent Hypothesis

• Life may have originated near hydrothermal vents on the ocean floor.

• These vents release hot, mineral-rich water, creating a suitable environment for chemical reactions.

• Some bacteria today still thrive in extreme conditions, supporting this theory.

C. Panspermia (Extraterrestrial Origin Hypothesis)

• Suggests life’s building blocks came from space, carried by comets or meteorites.

• Some meteorites contain organic molecules like amino acids, hinting at extraterrestrial contribution.

• While not widely accepted as the sole cause of life, it suggests life’s components could have originated beyond Earth.

D. RNA World Hypothesis

• Proposes that RNA was the first self-replicating molecule before DNA.

• RNA can both store genetic information and act as a catalyst for reactions.

• Over time, RNA evolved into more complex molecules, leading to cellular life.

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3. The First Living Cells

• The first life forms were simple prokaryotic cells (similar to bacteria).

• These cells absorbed nutrients from the environment and possibly performed simple chemical reactions.

• Some early life forms evolved photosynthesis, producing oxygen and changing Earth’s atmosphere.

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4. Importance of Understanding the Origin of Life

1. Explains Life’s Beginnings – Helps scientists understand how biological processes started.

2. Supports Evolutionary Theory – Shows how simple molecules evolved into complex organisms.

3. Guides Astrobiology Research – Helps scientists search for life on other planets (e.g., Mars, Europa).

4. Advances Medicine and Biotechnology – Understanding early biochemistry influences modern genetics and medicine.

5. AND we have a deep curiosity about the origin of us!

While the exact details remain uncertain, research continues to provide fascinating insights into how life emerged on Earth and potentially on other planets.

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Summary of learning objectives and key words or phrases

Appreciate some ideas of how life on Earth began.

Posing the question about the origin of life on Earth, I'm afraid there is no simple answer.

How did living organisms evolve from simple molecules and ions? How did life begin?

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