Question 1

What is half-life and how does carbon dating work?

Accepted Answer

**Half-life** is the time taken for half the atoms in a sample of a radioactive isotope to decay. It is a fixed property of each isotope, unaffected by temperature, pressure or chemical state.

**Why it is a half rather than a fixed amount.** Radioactive decay is **random** for any individual atom — there is no way to predict when a particular nucleus will decay. But with vast numbers of atoms, the statistics are extremely reliable: a constant **proportion** decays per unit time. This produces exponential decay, so after one half-life 50% remains, after two 25%, after three 12.5%, and so on.

**Carbon dating** applies this to organic material.

**Carbon-14 is continuously created** in the upper atmosphere when cosmic rays convert nitrogen into carbon-14. It mixes into atmospheric CO₂ and enters the food chain through photosynthesis. While an organism is alive, it exchanges carbon with the environment, so its carbon-14 proportion matches the atmosphere.

**At death, exchange stops.** No new carbon-14 enters, and the existing carbon-14 decays with a half-life of about **5,730 years**. Measuring the remaining proportion gives the time since death.

**Its limits, which matter:**

**The range is roughly 50,000 years.** After about nine half-lives so little remains that measurement becomes unreliable. Carbon dating cannot date dinosaurs, and it cannot date rocks.

**Only organic material** works — bone, wood, charcoal, textiles, shell.

**Calibration is required.** Atmospheric carbon-14 has varied over time, so raw results are corrected against calibration curves built from tree rings, corals and ice cores. Fossil fuel burning has also diluted atmospheric carbon-14 while nuclear testing spiked it.

**Other isotopes cover longer timescales** — uranium-lead and potassium-argon dating handle rocks and are how the Earth's age is established.

Question 2

What is an isotope, and why do isotopes matter?

Accepted Answer

Atoms of the same element with different numbers of neutrons — so they share chemical behaviour but differ in mass and, crucially, in nuclear stability. The distinction that defines it. An element is

Question 3

How do we know how old the Earth is?

Accepted Answer

Principally from radiometric dating of meteorites, which give an age of approximately 4.54 billion years — and the reason meteorites are used rather than Earth rocks is itself the interesting part.

Question 4

How does fossilisation actually happen?

Accepted Answer

Rarely, and through several different processes — the important point being that fossilisation requires an unusual sequence of events, which is why the fossil record is a biased sample of past life

Question 5

How does the geological time scale work?

Accepted Answer

A hierarchy of named intervals dividing Earth's history, defined by changes in the rock and fossil record rather than by round numbers — which is why the boundaries fall at irregular dates. The

Question 6

Why do we age?

Accepted Answer

There is no single answer, and the honest position is that ageing is multi-causal — a set of interacting processes rather than one clock running down. Researchers have converged on a list of

Question 7

What causes ice ages?

Accepted Answer

A combination of orbital variations setting the rhythm and feedbacks within the climate system amplifying them — with the underlying precondition being a continental arrangement that permits ice

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