A companion to Chapter Two
Look a little longer.
There was only so much I could put into a poem. Here, you can see some of it for yourself. Start wherever you like. You might find yourself staying longer than you meant to.
NASA / NOAA / GSFC · Composite image
01 Sunlight
What it takes to light your room.
While you read this sentence, the Sun is converting millions of tonnes of its own mass into energy. Every second, about four million tonnes. A tiny share of that energy reaches Earth, after travelling for roughly eight minutes.
The patch of light on your floor has come a long way.
A closer look
Deep inside the Sun, hydrogen nuclei fuse to form helium. The resulting helium has slightly less mass than the particles that went into making it. That difference is released as energy.
The eight-minute journey begins when light leaves the Sun's surface. Getting energy out from the core is a much longer process. The film below compresses ten years of observations into just over an hour. You can watch the Sun change rather than think of it as a still yellow circle.
A Decade of Sun
NASA Goddard · 61 minutes02 A place to live
The Moon gets sunlight too.
The Moon is practically our neighbour. It travels around the Sun with us, at almost the same distance. Yet its surface can reach about 127°C in full sunlight and fall to about −173°C in darkness.
Being the right distance from a star is only the beginning. An atmosphere can hold warmth and move it around. Take Venus: it is farther from the Sun than Mercury, but hotter. Its thick atmosphere traps so much heat that its surface could melt lead.
A closer look
The habitable zone is the range of distances where a planet could have liquid water on its surface, given a suitable atmosphere. It is sometimes called the Goldilocks zone. It doesn't tell us that a planet has water, an atmosphere or life.
Earth's air helps keep the surface warm enough for liquid water across much of the planet. The Moon has only a very thin exosphere, so it cannot redistribute heat as our atmosphere does. And water alone doesn't settle the question of life: scientists think Europa, a moon of Jupiter, has an ocean beneath its ice. We have yet to find life there.
There is no single agreed checklist that guarantees life. Each discovery gives us more to investigate.
What Is the Habitable Zone?
NASA · A short introduction03 The ocean
So much of it is too small to see.
Ask where oxygen comes from and most of us picture trees. Roughly half the oxygen produced on Earth each year comes from the ocean. Much of that work is done by drifting organisms so small you need a microscope to see them.
They take in sunlight near the surface. Whole marine food webs begin with them. You could look out over the sea for an hour and never notice what was doing so much of the work.
A closer look
These organisms include phytoplankton: microscopic algae and photosynthetic bacteria. Like plants on land, they release oxygen through photosynthesis.
The ocean also uses roughly as much oxygen as it produces, through respiration and decay. So this figure doesn't mean half of your next breath was made in the sea today. The oxygen in our atmosphere has accumulated over hundreds of millions of years. The story is larger, and older, than a single breath.
The Sun's Cycle Transforms the Sea
David Attenborough · BBC · 2 minutes04 Look nearby
Then there is the world at your feet.
A seed has to get somewhere it can grow. Some travel on the wind. Some float. Some hitch a lift on an animal. We step over them, brush them off our clothes, sweep them from the path.
Watch David Attenborough hold a few in his hands. Something you might have walked past becomes worth stopping for.
A closer look
Seeds carry a plant embryo and usually a supply of food, protected by a coat. Dispersal helps new plants reach places where they may find enough light, water and space. The shapes you see in the film help different seeds travel in different ways.
You don't have to wait for a trip somewhere spectacular to notice this. Look at what is growing beside the pavement on your way home.
A Lesson on Seeds
David Attenborough · BBC EarthThis is what I wanted you to have time for after the poem. To look at something you usually pass by, and stay with it long enough to notice what you had missed.
For me, learning how these things work gives me more reason to be grateful to Allah. The explanation itself is something worth understanding.
“And how many a sign within the heavens and earth do they pass over while they, therefrom, are turning away.”
Surah Yusuf, 12:105 · Saheeh International