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  • We've all seen movies

  • about terrible insects from outer space

  • or stories of abduction by little green men,

  • but the study of life in the universe,

  • including the possibility of extraterrestrial life,

  • is also a serious, scientific pursuit.

  • Astrobiology draws on diverse fields,

  • such as physics,

  • biology,

  • astronomy,

  • and geology,

  • to study how life was formed on Earth,

  • how it could form elsewhere,

  • and how we might detect it.

  • Many ancient religions described

  • other worlds inhabited by known human beings,

  • but these are more like mythical realms

  • or parallel universes

  • than other planets existing

  • in the same physical world.

  • It is only within the last century

  • that scientists have been able

  • to seriously undertake the search

  • for extraterrestrial life.

  • We know that at the most basic level

  • organisms on Earth need three things:

  • liquid water,

  • a source of energy,

  • and organic, carbon-based material.

  • We also know that the Earth

  • is just the right distance from the Sun,

  • so as not to be either frozen or molten.

  • So, planets within such a habitable range

  • from their own stars

  • may be able to support life.

  • But while we used to think

  • that life could only exist

  • in such Earth-like environments,

  • one of the most amazing discoveries of astrobiology

  • has been just how versatile life is.

  • We now know that life can thrive

  • in some of the most extreme environments

  • that'd be fatal for most known organisms.

  • Life is found everywhere,

  • from black smoke of hydrothermal vents

  • in the dark depths of Earth's oceans,

  • to bubbling, hot, acidic springs

  • on the flanks of volcanoes,

  • to high up in the atmosphere.

  • Organisms that live in these challenging environments

  • are called extremophiles,

  • and they can survive at extremes

  • of temperature,

  • pressure,

  • and radiation,

  • as well as salinity,

  • acidity,

  • and limited availability of sunlight,

  • water,

  • or oxygen.

  • What is most remarkable about these extremophiles

  • is that they are found thriving in environments

  • that mimic those on alien worlds.

  • One of the most important of these worlds

  • is our red and dusty neighbor, Mars.

  • Today, astrobiologists are exploring places

  • where life might once have existed on Mars

  • using NASA's Curiosity rover.

  • One of these is Gale Crater,

  • an impact crater created

  • when a meteor hit the surface of Mars

  • nearly 3.8 billions years ago.

  • Evidence from orbit suggest past traces of water,

  • which means the crater

  • might once have supported life.

  • Planets are not the only places

  • astrobiologists are looking at.

  • For example, Europa, one of the moons of Jupiter,

  • and Enceladus and Titan,

  • two of Saturn's moons,

  • are all exciting possibilities.

  • Although these moons are extremely cold

  • and two are covered in thick ice,

  • there is evidence of liquid oceans beneath the shell.

  • Could life be floating around in these oceans,

  • or could it be living around black smoker

  • vents at the bottom?

  • Titan is particularly promising

  • as it has an atmosphere

  • and Earth-like lakes, seas, and rivers

  • flowing across the surface.

  • It is very cold, however,

  • too cold for liquid water,

  • so these rivers may instead be flowing

  • with liquid hydrocarbons

  • such as methane and ethane.

  • These are composed of hydrogen,

  • and, more importantly, carbon,

  • which is the basic building block

  • of all life as we know it.

  • So, could life be found in these lakes?

  • Although instruments are being designed

  • to study these distant worlds,

  • it takes many years to build them

  • and even longer to get them

  • where they need to be.

  • In the meantime, astrobiologists work

  • in our own natural laboratory, the Earth,

  • to learn about all the weird

  • and wonderful forms of life that can exist

  • and to help us one day answer

  • one of humanity's oldest questions:

  • Are we alone?

We've all seen movies

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B1 US TED-Ed life earth crater liquid liquid water

【TED-Ed】Why extremophiles bode well for life beyond Earth - Louisa Preston

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    Kevin Tan posted on 2014/08/12
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