We finally start the tale of Earth’s history from the beginning, in the cold depths of outer space. The Sun is born and the first asteroids assemble. When these asteroids crash into Earth today, they provide time capsules from the beginning of the solar system.

Extra credit: look for the Orion Nebula in the night sky, or go meteorite hunting with a friend.

How did Earth grow from ant-size to, well… Earth-size? What perils did it face along the way? And how was the early Earth like a fine vinaigrette?

Extra credit: try to freeze a mixture of oil and vinegar before they separate.

How has the Sun changed over the past 4 billion years?

While the Sun may seem unalterable, it has brightened dramatically over Earth's history, with major implications for our world. Today, we'll meet a team of women who catalogued thousands of stars in the 1800s, play in a galactic ball pit, and puzzle over a cosmic paradox alongside Carl Sagan.

Extra Credit: Watch Cosmos (1980)

If the sun was dimmer 4 billion years ago, how did the Earth stay warm?

Today, we learn how just a small percent of Earth's atmosphere goes a long way in controlling global climate, both today and in the ancient past. Along the way, we'll visit an imaginary frozen Earth without any sun, a hazy giant moon of Saturn, and learn exactly what the greenhouse effect is.

Extra credit: Visit a greenhouse, or find a cleaning product with ammonia.