THE MYSTERIOUS ORIGINS OF LIFE ON EARTH

 Billions of year ago on the young planet Earth simple organic compounds assembled into more complex coalitions that could grow and reproduce. They were the very first life on Earth, and they gave rise to everyone one of the billions of species that have inhabited our planet since. At the time, Earth was almost completely devoid of what we'd recognize as a suitable environment for living things. The young planet had widespread volcanic activity and an atmosphere that created hostile conditions. So where on Earth could life begin?

To begin the search for the cradle of life, It's important to first understand the basic necessities for any life form. Elements and compounds essential to life include hydrogen, methane, nitrogen, carbon dioxide, phosphates, and ammonia. In order for these ingredients to comingle and react with each other, they need a liquid solvent:water. and in order to grow and reproduce, all life needs a source of energy. Life forms are divided into two camps : autotrophy, like plants, that generate their own energy, and heterotrophs, like animals, that consume other organism for energy. The first life form wouldn't have had other organisms to consume, of course, so it must have been an autotroph, generating energy either from the sun or from chemical gradients. So what locations meet these criteria? Places on land or close to the surface of the ocean have the advantage of access to sunlight. But at the time when life began, the UV radiation on earth's surface was likely too harsh for life to survive there. One setting offers protection from this radiation and an alternative energy source: the hydrothermal vents that wind across the ocean floor, covered by kilometers of seawater and bathed in complete darkness. a hydrothermal vent is a fissure in the Earth's crust where seawater seeps into magma chambers and is ejected back out at high temperatures, along with a rich slurry of minerals and simple chemical compounds. energy is particularly concentrated at the steep chemical gradients of hydrothermal vents. There's another line of evidence that points to hydrothermal vents: the last universal common ancestor of life, or LUCA for short.

LUCA wasn't the first life form, but it's as far back as we can trace. Even so, we don't actually know what LUCA looked like-there's no LUCA fossil, no modern-day LUCA still around-instead, scientists identified genes that are commonly found in species across all three domains of life that exist today. since these genes are shared across species and domains, they must have been inherited from a common ancestor. These shared genes tell us that LUCA lived in a hot, oxygen-free place and harvested energy from a chemical gradient-like the ones at hydrothermal vents. there are two kinds of hydrothermal vent: black smokers and white smokers. Black smokers release acidic, carbon-dioxide-rich water, heated to hundreds of degree celsius and packed with sulphur, iron, copper, and other metals essential to life. But scientists now believe that black smokers were too hot for LUCA- so now the top candidates for the cradle of life are white smokers. Among the white smokers, a field of hydrothermal vents on the Mid-Atlantic ridge called Lost City has become the most favoured candidates for the cradle of life. the seawater expelled here is highly alkaline and lacks carbon dioxide, but is rich in methane and offers more hospitable temperatures. adjacent black smokers may have contributed the carbon dioxide necessary for life to evolve at Lost City, giving it all the components to support the first organisms that radiated into the incredible diversity of life on earth today.

IS THERE LIFE BEYOND EARTH?

Astronomers reckon there might be tens of billions of planets out there that are at least a little bit like this one, but we've only found life on one of them. Here on earth, life popped up pretty much as soon as it could. Around three and a half billion years ago, after comets had bombarded Earth with water, and volcanes had belched out an atmosphere, it was POOF, life!

Maybe, out there in the universe, wherever the ingredients for life are right, it might just happen. Eventually, and I'm fast forwarding through just a little bit of Earth's history here, some of that life became intelligent. As intelligent species go, humans are the only one s capable of having an existential crisis. We capable of having an existential crisis. we just very badly don't want to be alone in the universe. Now we're looking for other intelligent life out there. But what exactly are we looking for? What would intelligent life look like? well, no. Yeah,but no. Let's pretend we launch a spacecraft to fly by a rocky planet that sits habitable zone of its star. The first thing we'd see is that it's covered in water, on the surface and in the air. And there's way too much oxygen and methane in the atmosphere. Its gets weirder. there's something covering the land that's absorbing a ton of red light. And this planet is screaming with radio signals. We've discovered a planet with life! This space mission actually happened. Back in 1990, when the galileo spacecraft flew by earth on its way to Jupiter, Carl Sagan had an idea. To give us an idea of what we'd see if we found a planet that holds life, we should start by looking at our own. But life out there might not look like life on Earth. Assuming that everything  out there is just like us, would be like an alien landing on earth and finding a platypus, and deciding that everything down here looked like the result of a beaver's late-night encounter with a duck.

The nearest Earth-like planet might be twelve light year away, that's a 200,000 year one-way trip for a spacecraft like Voyager. the key to finding life on other planets, might be zipping through the air all around you.Now, civilization could probably live happily ever  after without radio. It worked for the aztecs. But no matter intelligent a life form is, without radio signals they might as well be invisible to the galaxy. Luckily, we are not invisible. we've been beaming out signals to the universe for over a century.