Stop 1. The whole span

Look at the top strip of Chart 1. One even scale runs from the beginning of the universe on the left to billions of years from now on the right. The red line is now.

The universe began 13.787 billion years ago, give or take 20 million. That figure comes from the Planck satellite's map of the oldest light in the sky. The earth formed about 4.54 billion years ago. Rocks from space and the decay of lead give that date. By about 4.4 billion years ago there was liquid water. Tiny crystals from western Australia show it.

The earliest life that scientists broadly accept is about 3.48 to 3.43 billion years old. Older claims go back past 3.7 billion, but they are disputed. Oxygen filled the air between about 2.46 and 2.06 billion years ago. Animals burst onto the scene about 538.8 million years ago.

Now look right of the red line. That purple zone is the future, as science models it. In about a billion years the Sun will be bright enough to start boiling the oceans away. About 5.4 billion years from now it will leave its main life and swell into a red giant. One careful study puts the end for the earth at about 7.59 billion years from now: the Sun will swallow it. Some older studies thought the earth would escape.

That is the longest horizon on either chart. We will come back to it at the end.

Picture: Chart 1, strip 1.