All around us both inside and outside there are many life forms. These life forms live in forests, caves, under rocks, in ponds and puddles, deserts, oceans, glaciers, in our cities and in many other places. All of us share a larger home. This home is the planet Earth. But, how did we all get here? How and when the story of life began?
The origin of life might seem like the ultimate cold case, no one was there to observe it and much of the relevant evidence has been lost in the intervening billion years. Earth is estimated to be 4.5 billion years old, and for much of that history it has been home to life in one weird form or another. Indeed, some scientists think life appeared the moment our planet’s environment was stable enough to support it.
Birth of the Earth
Most astronomers believe the universe began in a Big Bang about 14 billion years ago. At that time, the entire universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine. Everything in the Universe, all the galaxies, stars, planets, and even the matter making up your body, was squished up tightly in this tiny space. Eventually, after a very long time, this speck exploded. All of a sudden, in a giant flash of unimaginable heat and power, the universe was born. Over a period of billions and billions of years, the universe became what we see today. Slowly stars began to form, and around these stars planets formed.
In a quiet galaxy known as the Milky Way, there formed a medium sized yellow star which would come to be known as Sun. Around that sun formed eight planets. One of those planets, the third in distance from the sun, was our home, a small planet called Earth.
Studies of ancient rocks have shown that life began on the Earth 3,800 million years ago. At that time, the Earth was a very unfriendly place. The air was dense and poisonous. Comets and meteorites were raining down on the planet. For the first 500 million years, the Earth would remain as a giant lifeless ball of fiery lava. For another 300 million years after that, it would be too hot for liquid water to form.
Finally, after 800 million years, an unimaginably long period of time, our home planet cooled enough for liquid water to begin to form. Everywhere rains began to fall, filling the lower portions of the Earth with water, forming lakes, oceans and rivers.
The young Earth was a water world with small areas of dry land. Many scientists think that life began in the lakes and oceans. Many of the ingredients from which life started may have been brought by comets and meteorites. Many theories suggest that life began in the oceans.
Earth’s ancient oceans while lifeless, were filled with the chemicals needed for life. Lightning and ultraviolet light from the Sun may have split the hydrogen-rich gases in the atmosphere. Energy may also have come from hot springs on the sea bed, known as ‘black smokers’ (hydrothermal vents).
Over time, the simple chemicals joined to become larger, more complex chemicals. These chemicals were not alive, but they were there sloshing around. They call these chemicals “primordial soup.” Instead of alphabet letters, this soup was filled with amino acids, proteins, lipids, and other basic components that are commonly found in life forms today.
It is believed that life began on the shores of these ancient oceans in pools of water called tidal pools. These shallow pools would have been full of this “life soup”. Over many millions of years, as the ingredients of life splashed around in these pools, possibly helped by lightning strikes, they formed the first cells.