Threshold 4 · Earth and the solar system
The Early Earth
A disc of gas and dust around a young Sun becomes planets; one of them sorts itself into core, mantle and crust and grows oceans.
Nine billion years into the story, in an unremarkable arm of an unremarkable galaxy, a cloud enriched by generations of dead stars collapses into a new one. The leftovers form a disc, and the disc forms planets. One of them is ours.
This chapter is about how a planet is built and how it becomes a place where things can happen: the violent early years, the impact that made the Moon, the sorting of the Earth into layers, the arrival of oceans and air, and the slow machine of plate tectonics that still shapes the surface, including the collision that is raising the Himalaya.
It is also where we learn to read deep time, because rocks keep clocks, and the clocks tell us how old all of this is.
Lessons
- 4.1 From nebula to planetsDraft
How the solar system assembled from a disc of gas and dust.
- 4.2 Earth's violent birthPlanned
The Moon-forming impact and the magma ocean.
- 4.3 Core, mantle, crustDraft
Differentiation: how the Earth sorted itself into layers.
- 4.4 Plate tectonics and the HimalayaPlanned
The engine of a living planet, told through the Indian plate and the rise of the Himalaya.
- 4.5 Oceans and airPlanned
Where the water and the atmosphere came from.
- 4.6 Deep timePlanned
Radiometric dating: how we know the age of a rock.
- 4.7 Earth as a systemPlanned
Rock, water, air and life as one connected machine.