Question 1

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 sheets to form at all.

**The terminology first.** We are currently **in** an ice age — defined as a period with permanent ice sheets, which Greenland and Antarctica provide. Within an ice age, **glacial** periods are colder intervals with expanded ice, and **interglacials** are warmer ones. We are in an interglacial, the **Holocene**.

**The pacemaker: Milankovitch cycles.** Variations in Earth's orbit and orientation change how sunlight is distributed by latitude and season:

**Eccentricity** — how elliptical the orbit is, varying on roughly 100,000-year cycles.

**Obliquity** — the tilt of the axis, varying between about 22.1 and 24.5 degrees over roughly 41,000 years. Greater tilt means stronger seasons.

**Precession** — the wobble of the axis, on roughly 19,000 to 23,000-year cycles, determining which season occurs at closest approach to the Sun.

**Why summer matters more than winter.** The critical factor is whether **northern hemisphere summers are cool enough for winter snow to survive**. Ice sheets grow not because winters are snowier but because summers fail to melt what fell — which is why the northern hemisphere, with its large landmasses at high latitude, controls the rhythm.

**Why orbital changes alone are insufficient.** The change in total solar energy is small — far too small to produce the observed temperature swings. **Feedbacks amplify it:**

**Ice-albedo feedback.** Ice reflects sunlight; more ice means more reflection, more cooling, more ice.

**Carbon dioxide.** Ice core records show CO₂ falling during glacials and rising during interglacials, amplifying the orbital signal substantially. The ocean's capacity to hold carbon changes with temperature and circulation.

**Dust, vegetation and ocean circulation changes.**

**The longer-term precondition:** continental positions allowing polar ice, ocean gateways opening and closing, and long-term decline in atmospheric CO₂ through weathering of uplifted mountains.

**The 100,000-year problem** — why glacial cycles follow the weakest orbital cycle — remains incompletely resolved.

Question 2

What actually causes the seasons?

Accepted Answer

The seasons are caused by the tilt of Earth's rotational axis, about twenty-three and a half degrees relative to its orbital plane. They are not caused by distance from the sun, which is the most

Question 3

Why do we have leap years?

Accepted Answer

A year is the time Earth takes to orbit the sun, and that is not a whole number of days. It is approximately 365.2422 days. A calendar of exactly 365 days therefore drifts by nearly a quarter of a

Question 4

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 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 is the Earth's core still hot after billions of years?

Accepted Answer

Two reasons: heat left over from the planet's formation, and heat still being generated now by radioactive decay. Together they account for the roughly 5,000–6,000°C at the inner core — comparable to

Question 7

What is the difference between weather and climate?

Accepted Answer

Weather is the state of the atmosphere at a particular time and place. Climate is the statistical description of weather over a long period, conventionally thirty years, for a given region. The

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