Q: How did Earth get water, the necessary ingredient for life?
A: Experts believe asteroids or comets delivered water to Earth billions of years ago.
Q: How was the first-ever cell created?
A: Lightning struck water, its billions of volts of electricity causing chemical atoms to join up in a sequence to create a bundle of genetic material. On their own, the genes wouldn't have been able to survive in the hostile world of protean Earth, but a blob of oily material could have engulfed a single genetic chain, creating the first-ever cell.
Q: What was the first living thing?
A: The first cell copied itself, making a perfect clone: the first living thing.
Q: For how long were simple cells the only living things?
A: Simple cells were the only living things on Earth for two billion years.
Q: How did different species come to proliferate?
A: Two simple cells merged, combining their genes. When the merged cell cloned itself, its offspring had genes from both cells, both "parents." This simple "sex" gave rise to variation, because, as cells reproduce sometimes things go wrong and mutations pile up and differences arise. Finally the cells become so different that they are separate species.
Q: How were we first able to tell light from dark?
A: About 550 million years ago, our early lives as water worms began to change once a handful of skin cells mutated, allowing us, with new light-sensitive cells, to tell light from dark and find more prey while hiding from predators. Over untold generations, further mutations refined those cells to one day give our ancestors eyes.
Q: When did our ancestors first get a brain?
A: Some 521 million years ago, a tiny collection of nerve cells behind the eyes of a fish-like creature called Myllokunmingia clustered together. No bigger than the head of a pin, this tiny brain could make simple decisions and process basic information. This simple cluster of nerve cells evolved to become nature's most complex organ, the human brain.
Q: Of all species that have ever lived, how many are now extinct?
A: About 99 percent of all species that have ever lived are now extinct.
Q: Why did we first evolve jaws and teeth?
A: More than 400 million years ago fish-like Myllokunmingia -- early "us" -- faced predation from the bigger, stronger Anomalocaris, a kind of great white shark of its time. By 375 million years ago "we" were able to adapt into a foot-long armored fish with teeth and jaws.
Q: Why did we first leave the water for land?
A: Despite our ability to size up in the water, we were driven by larger predators into shallow, stagnant water, where we were too staved for oxygen. It took millions of years, but our ancestors were able to adapt to perform a first for fish: breathe air, which traveled into a new organ we call the lung. All because a monster fish called Anomalocaris chased us into shallow water.
Q: What species were we when we could first breathe air OR water?
A: We were Ichthyostega, able to close off our windpipe and switch between lungs and gills. (Today our gills are gone, but the mechanism remains - and sometimes spasms, giving us the hiccups.)
Q: How did we first adapt to life on land?
A: We evolved into a creature called Casineria, with thick skin to protect us from the sun and tough claws to help move across the rough terrain. Casineria was the first of our ancestors to live entirely on dry land.
Q: What happened to creatures when a giant plume of magma from a volcanic eruption surged up from deep inside the planet 250 million years ago?
A: The magma caused molten rock to ooze through cracks in the Earth's crust, covering an area the size of the United States under a layer 1,000 feet deep. This went on for half a million years! Trillions of tons of noxious carbon dioxide trapped the sun's heat inside the atmosphere. Temperatures soared to more than 100 degrees. Plants, the plant eaters, and eventually the meat eaters perished. Of all species, 95 percent died while a few were able to hang on; "we" were among those few.
Q: How did we change after the volcanic eruption?
A: At the time of the eruption, we looked like large lizards. But 30 million years after the event, we became a cat-sized creature covered in fur called Ecteninion.
Q: How did our "ancestors" adapt to the threat and presence of the dinosaurs?
A: Over millions of years, we got smaller and harder to catch, nocturnal and harder to see. We became Batodon, a two-inch-long shrew like creature. Inside our brain a new structure evolved: the neocortex, home of complex thought, allowing us to analyze a situation and respond. Today, the neocortex is what gives us the power to imagine, create and communicate.
Q: How did we protect our offspring from dinosaurs?
A: To protect our offspring from hungry dinosaurs, we evolved to give birth to live young. Instead of leaving them to fend for themselves; we nurtured them with milk. Sweat glands evolved to become mammary glands. The mammals had arrived.
Q: How did we survive the meteor strike 65 million years ago that killed the dinosaurs?
A: As a small rat-like mammal, we were able to dig to protect ourselves. Dinosaurs, meanwhile, were big creatures with enormous food needs. A world blotted out in ashen skies could not support them. Their dying carcasses fed bug populations, which, in turn, fed our rat-selves. Sixty-four million years ago, we became our bug-eating ancestor Purgatorius - standing just 6 inches long - the unlikely inheritors of the dinosaurs' crown. Mammals became the dominant animal species on land.
Q: When did we first become primates?
A: Sixty million years ago, we became Altiatlasius, one of the first members of a new group of mammals - the primates.
Q: How did changing temperatures encourage our evolution?
A: More than 10 million years ago, extreme temperatures ravaged the forests, which got smaller, making the food harder to reach. Our tail shrank back to the base of the spine, to what is now the coccyx. Instead of leaping, we began to stretch -- our arms growing longer and more flexible.
Q: When did we first take steps on two legs?
A: About 4.4 million years ago we, more precisely Ardipithecus, took our first-ever steps on two legs. We could walk to the food with our hands free to pick it. It caught on fast. Ardipithecus was smart enough to copy and learn: Walking was passed from parent to child. Over the next 1.2 million years, our body evolved so that we could walk farther and faster. Finding shelter, a mate, and food became easier.
Q: Why do we spend years caring for our offspring?
A: As we evolved, we took on a narrower pelvis, which made giving birth to a fully developed infant impossible. Babies therefore have to come out early, when their heads are smaller and they're barely developed. That's why we are one of the few species to spend years caring for our offspring -- protecting them, feeding them and keeping them out of trouble.
Q: Who was "Handy Man"?
A: "Handy Man" was Homo Habilis -- "us" 2.3 million years ago: Walking on two legs, with a big brain, Homo Habilis was the first of an entirely new type of creature - the first man. He was a solo scavenger, who ate whatever he could find. He was also the first species to make tools.
Q: How many bones become fossils?
A: Fewer than one bone in a billion becomes a fossil. Factor in the chances of finding those bones across millions of square miles of Earth and it's clear that most of what has lived has been lost. All the bones of our early human ancestors ever found would fit in the back of a pick-up truck.
Q: With what species did we move from scavengers to hunters?
A: Homo Erectus, some 1.8 million years ago, were hunters who also learned how to work with other members of our species. They also used fire for warmth and cooking. (Their cooked meat, easier to chew, caused their powerful rear-most molars to retreat back into their gums, where they remain as our wisdom teeth.)
Q: How did we evolve speech?
A: Our tongue changed shape and moved down our throat, carrying the larynx with it. This allowed us to form different shapes in our mouths, make different sounds and ultimately make words. Speech remains our greatest tool; it was the last piece of the puzzle that turned our ancestors into us.
Q: When did modern man, Homo Sapiens, arrive on the scene?
A: Homo Sapiens (meaning "wise man") appeared about 200,000 years ago, boasting pound-for-pound the largest brain of any creature on Earth, with superior intelligence and the tools to spread out across every continent of the planet.