Did Earth Always have water ? A cosmic H2origin story.....

The Earth's is covered in water. That’s every last drop in the oceans, inclouds, in icecaps, in your body. And even less of that is fresh water. All that water together would fill a sphereonly 860 miles (about 1,385 kilometers) in diameter. Water is one of the things that makes Earthso special and without it, life as we know it couldn’t exist. Was our home always a waterpark? If not, how did it all get here? What do we really know about Earth’s H-two-Origins? [INTRO] The solar system formed when a cloud of gasand dust collapsed into a swirling disk. And at least some of that cloud was water. In the orbit where Earth would one day be,the young sun’s intense heat prevented water vapor from condensing on its own. But tiny grains of dust acted as ‘condensationnuclei’ to let droplets form. These tiny debris particles coalesced intoour young planet along with the water they carried. As Earth cooled, rocks in the crust reactedwith chemicals in the early atmosphere to create more water molecules. Water existed inside Earth's mantle, but notas independent H-two-O molecules, rather it separated into H’s and OH’s in the rock. We don’t know exactly how much water isstill locked inside Earth today, but there may be several oceans' worth of primordialH2O embedded within minerals, or even as ice inside diamonds deep underground. This explains some of Earth’s water, butmuch—if not most—of the water on the surface today was imported from farther out in thesolar system. One type of asteroid called a ‘carbonaceouschondrite’ contains water molecules, and also their raw ingredients, oxygen and hydrogen. During the early years of the solar system,we think Jupiter may have orbited closer to the Sun than it does today. Its gravity would’ve flung thousands ofthese watery asteroids toward the young Earth. But comets also hold a lot of water ice, andthere are billions of them zipping around the solar system. If they crashed into early Earth they couldhave brought water too. So how can we tell if most of our water camefrom asteroids or comets? Every water molecule contains two hydrogenatoms and one oxygen. But a tiny fraction of the hydrogen atomsin water have an extra neutron in their nucleus. Comet water and asteroid water have differentratios of these heavy hydrogens to normal hydrogens. The atomic fingerprint of the water we findon Earth doesn’t quite match what we see in comets, but the water in asteroids is acloser match. Like many things in science, we can’t be100% sure yet, but so far it seems that most of our water came from asteroids. So Earth probably got its water in multipleways. Some was built into the planet. Earth made a bit on its own. And the rest—was delivered by space rocks. But where did all this water come from…before the solar system? Astronomers have detected water all over thecosmos. They've seen it in clouds of gas between starsand in other planet-forming disks. Around one supermassive black hole, they'veeven detected a reservoir of water 140 trillion times heavier than Earth's oceans. This space fog is far enough away that it,and its water, must have existed at least 12 billion years ago, and maybe earlier. So how old is the universe’s oldest water? All of the universe's hydrogen was made duringthe Big Bang, but oxygen is only produced inside the nuclear furnace of stars. So water could have formed as soon as thevery first stars in the universe ignited, about 12.7 billion years ago at the earliest. A tiny fraction of the air we breathe–andthe water we drink today–contains some of these very first oxygen atoms. Why do we care so much about the history ofsomething as seemingly boring as a glass of water? The earlier there was water in the universe,the earlier there could've been watery planets. And the earlier there were watery planets,the more time there could be for life to evolve. That’s a refreshing thought. Stay curious. Thank you to brilliant dot org for supportingPBS Digital Studios. Water has been essential to the developmentof life on Earth, but knowing the age of water, and where water might exist in our galaxyis one of the best clues astronomers have for figuring the odds of extraterrestriallife. How do astronomers actually LOOK for otherworlds though? If you’re *thirsty* for answers to thatand other astronomy questions, Brilliant has a course all about astronomy. It includes a breadth of knowledge about thecosmos, and lessons like “Worlds Beyond Earth” teach you the tools that astronomersuse to search for and study planets outside our own solar system. Brilliant’s lessons are broken up into bite-sizepieces, with instruction designed to guide you through problems. Learning about astronomy is about more thanfacts and memorizing. Staying curious is about learning how to learnanything. Brilliant – Math and Science Done Right,proud to support It’s Okay to Be Smart. To learn more about Brilliant, go to brilliantdot org slash BESMART.