Origins of Life on Earth
Introduced| English |
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| organic molecules/ɔːˈɡænɪk ˈmɒlɪkjuːlz/ |
Where did the first life come from?
- Natural selection explains how life changed — but not how it first began.
- The earliest cells appeared on Earth billions of years ago.
- Before them, there was only chemistry, no biology.
- How that chemistry became the first living cell is one of science's great questions.
A very different young Earth
- Early Earth was hot, with volcanoes, lightning, and no free oxygen.
- Its air held simple gases, and its surface held water.
- These provided the ingredients and the energy for reactions.
- The stage was set for chemistry to become complex.
What did early Earth provide that could drive chemical reactions?
Early Earth had energy from lightning, volcanoes, and sunlight — but little free oxygen and no life yet.
Building organic molecules
- Given energy, simple gases can react to form small organic molecules 有机分子.
- The famous Miller-Urey experiment showed this in the lab, making amino acids.
- Over time, these small molecules could join into larger polymers, including RNA.
- Step by step, the chemistry grew more life-like.
From chemistry to the first cell
Step through how simple chemicals on early Earth may have built up into the first living cells.
The Miller-Urey experiment showed that early-Earth conditions could form…
Miller and Urey made organic molecules (amino acids) from simple gases and energy — a key first step.
The first cells
- Molecules that could copy themselves had a huge advantage.
- Wrapped inside simple membranes, they formed the first cell-like structures.
- Once such a structure could copy itself, life — and natural selection — could begin.
- From that first cell, all of today's diversity slowly branched out.
Life is thought to have built up gradually: small molecules, then polymers, then cells.
The steps build up: simple molecules, then larger polymers, then membrane-enclosed self-copying cells.
Once the first cells existed, the diversity of life arose through natural ____.
The origin of the first cell is separate from natural selection, which then produced all later diversity.
Select all true statements about the origin of life.
Life is thought to have built up gradually, not appeared instantly. The other three are correct.
This lesson is about the origin of the first life — a chemistry question. It is separate from natural selection, which explains the diversity of life after the first cell existed. Do not use "evolution" to mean the origin of life itself.
The Miller-Urey experiment:
- In 1953, scientists sealed simple gases and water in a flask and added sparks (like lightning).
- After days, the flask contained amino acids — the building blocks of proteins.
- It showed that life's ingredients can form from non-living chemistry, given energy.
The origin of life asks how the first cell arose from chemistry. On early Earth, energy drove simple gases to form organic molecules (shown by Miller-Urey), which built up into polymers and eventually membrane-enclosed, self-copying cells. This is a separate question from natural selection, which then produced all later diversity.