Nova

In April 1775, war breaks out in Britain's most troublesome territory.

In April 1775, war breaks out in Britain's most troublesome territory.

In April 1775, war breaks out in Britain's most troublesome territory.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

The rocky planets - Mercury, Venus, Earth and Mars - were born of similar material around the same time, yet only one supports life.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

The rocky planets - Mercury, Venus, Earth and Mars - were born of similar material around the same time, yet only one supports life.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

The rocky planets - Mercury, Venus, Earth and Mars - were born of similar material around the same time, yet only one supports life.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Thousands of prehistoric footprints in New Mexico's White Sands National Park capture moments when Ice Age humans crossed paths with enormous ground sloths and mammoths.

For decades, scientists have tried to unlock the secrets of ancient DNA.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Mars was once a blue water world studded with active volcanoes.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Thousands of engineers, technicians and workers race to build Europe's biggest construction project-London's new railroad, the Elizabeth Line.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Mars was once a blue water world studded with active volcanoes.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Mars was once a blue water world studded with active volcanoes.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Dogs have long been dependable companions by our sides.

Worshiped as a goddess, condemned as satanic and spun into a stunning array of breeds, cats have long fascinated humans.

Jupiter's massive gravitational force made it a wrecking ball when it barreled through the early solar system.

Dogs have long been dependable companions by our sides.

Worshiped as a goddess, condemned as satanic and spun into a stunning array of breeds, cats have long fascinated humans.

Dogs have long been dependable companions by our sides.

Worshiped as a goddess, condemned as satanic and spun into a stunning array of breeds, cats have long fascinated humans.

Dogs have long been dependable companions by our sides.

Following a trail of fossils found in all the wrong places -- beech trees in Antarctica, redwoods and hippo-like mammals in the Arctic -- uncover the bizarre history of the poles, from miles-thick ice sheets to warm polar forests teeming with life.

Worshiped as a goddess, condemned as satanic and spun into a stunning array of breeds, cats have long fascinated humans.

A visionary astronomer in West Africa attempts a high-stakes observation of a distant asteroid vital to a NASA mission.

Dogs have long been dependable companions by our sides.

Worshiped as a goddess, condemned as satanic and spun into a stunning array of breeds, cats have long fascinated humans.

Jupiter's massive gravitational force made it a wrecking ball when it barreled through the early solar system.

Dogs have long been dependable companions by our sides.

Worshiped as a goddess, condemned as satanic and spun into a stunning array of breeds, cats have long fascinated humans.

Jupiter's massive gravitational force made it a wrecking ball when it barreled through the early solar system.

Scientists investigate colossal explosions in Siberia and other evidence that rapidly melting soil in the Arctic is releasing vast amounts of methane, a potent greenhouse gas.