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[Music]
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what is life where did we come from
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water is h2o two atoms of hydrogen and
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one of oxygen pulled together by
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covalent bonds the air we breathe is a
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mix of countless particles along with
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dust and water vapor then what is it
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that makes up life what are the
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ingredients of our fundamental essence
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and what is it
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that separated us nearly four billion
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years ago and continues to separate us
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today from everything else
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oh no doubt many individuals in the
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ancient world concern themselves with
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these great questions it was the Greeks
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from around the seventh century BC
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onwards who turned it into a viable
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career path many philosophers of the
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Greek world the like of Epicurus
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Lucretius and Plato be occupied
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themselves with where life came from the
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overwhelming conclusion was that life
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baguettes life but what of the first
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life what began that in the fourth
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century BC Aristotle concluded that
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living things arise spontaneously from
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nonliving matter as long as that matter
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contained in nuuma or vital heat worms
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he surmised arose spontaneously from
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decaying manure insects sprang forth
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from the morning dew and eels
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Servet newborn from nothing more than a
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wet booze and rotting seaweed remarkable
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as this may seem to us now Aristotle's
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ideas of spontaneous generation
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dominated thinking on the origin of life
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for nearly 2,000 years the scientists
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that followed in his footsteps devising
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ever more complex recipes for higher
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forms of life like early 17th century
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Dutch scientist jean-baptiste van
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Helmont who reasoned that a dirty shirt
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left in a bin with wheat germ for 21
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days but spontaneously generate live
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mice
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over time though the recipes for
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spontaneous life lost favor science
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advanced and explanations were found for
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the seemingly miraculous appearance of
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animals in old abandoned heaps of dirt
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but for the smaller enigmatic creatures
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bacteria and weird single-celled amoebas
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spontaneous generation proved hard to
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disprove finally in the 19th century
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French biologist Louis Pasteur devised
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an experiment to exclude any outside
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influence from a flask full of inanimate
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matter a vacuum when the flask remains
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sterile the concept of spontaneous
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generation was proved to be false matter
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alone could not make life after all to
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this day no laboratory has been able to
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pull life from its absence Frankenstein
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remains a fiction life and only life has
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continued to beget life and yet we know
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today that the earth formed more than
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four billion years ago without life no
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living thing could have survived the
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convulsions of the Hadean Eon but here
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we are today on an earth brimming with
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overflowing with living beings of every
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imaginable form and function from
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rainforest to desert from the highest
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peaks to the deepest ocean depths life
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thrives
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so it is abundantly clear at some point
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between three to four billion years ago
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matter did make life the final act of
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spontaneous generation in history the
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origin of life on earth the questions
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that remain a how and from what
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[Music]
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the first life on earth must have been
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the simplest possible life form no mice
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could have sprouted spontaneously into
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being on a late Hadean Eon earth in
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order to decipher where life came from
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we must first consider what exactly life
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is at its most basic level a monumental
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task requiring all the efforts of modern
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scientific technique in most education
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systems humans learn to define living
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things by what they do animals plants
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and fungi taking steps to maintain
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themselves grow and reproduce but this
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isn't the full story living creatures
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might do these things but they're not
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the only ones by this definition we
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would class some crystals as being alive
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or computer viruses algorithms even
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today this is not the standard
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definition for the origin of organic
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life on Earth instead we need to zoom in
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to the microscopic level to see what
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living things are made of
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the simplest forms of life today
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bacteria have two basic ingredients a
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self-replicating molecule like DNA that
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contains the instructions for making
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another one of itself and a
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self-contained metabolism that provides
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the machinery to do the living and the
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replicating defined like this we capture
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the essence of every living thing on
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planet Earth everything is made up of
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cells like the bacterial cell which at
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their core have a self-replicating
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molecule and a self-sustaining
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metabolism this definition gives viruses
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a place on the road to life - even if
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they don't quite qualify these tiny
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structures have a self-replicating
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molecule within them just like every
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other living thing but they lack the
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machinery to do anything with that
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molecule instead they must hijack other
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organisms to borrow the organic
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factories that will allow them to
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reproduce some scientists would class
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them as alive others would not some even
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think that they may be a piece in the
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puzzle of life's origins a kind of
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halfway point between living and dead so
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a self-replicating molecule and a
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metabolism were the two inventions
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needed for the very first life-forms but
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they're not simple inventions
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our DNA is a giant complex macromolecule
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a long double strand made up of millions
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of smaller simpler molecules they
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themselves built from atoms of carbon
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oxygen hydrogen nitrogen and many more
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the modern metabolism built around this
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monster molecule is a complex organic
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factory to each part finely tuned to a
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particular function and interdependent
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on everything else
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to keep running of course life couldn't
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start out with something so elaborate
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its beginnings were necessarily much
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simpler using basic building blocks that
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already existed on the early earth or
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that were made for the first time inside
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its young oceans so to find the true
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beginning we have to go back and examine
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the chemical composition of this young
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world of all the possible elements in
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the universe 94 occur naturally on our
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planet
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every element is characterized by its
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behavior its affinity for other elements
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and the energy needed to make or break
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connections some don't react at all
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others like silicon react slowly needing
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huge amounts of energy to restructure
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its molecules silicon is abundant on the
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earth but not a good candidate for
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shifting reactive biological life carbon
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is a stronger choice the fourth most
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common element in the solar system it
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can easily form strong bonds with other
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carbon atoms as well as with other
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abundant elements oxygen hydrogen
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nitrogen all life on Earth is based on
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this cosmopolitan
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element combined with oxygen and
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hydrogen in what are now called organic
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molecules
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in fact the Hadean earth was a melting
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pot of organic opportunity
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sugars which were destined to become the
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backbone to our genetic molecules and
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the fuel for our cellular factories were
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made with cosmic chemistry and formed in
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the star forming regions of the Milky
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Way they floated freely in the early
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ocean nuclear bases to simple nitrogen
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containing compounds that when combined
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form the basis for information storage
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in our self-replicating molecules the
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molecular language of life's instruction
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manual a repeating pattern of four
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different nuclear bases encodes all the
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instructions for how to stay alive grow
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and reproduce on the early earth they
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could have been a spontaneous product of
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primordial chemistry finally amino acids
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also ubiquitous to all life on Earth
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they are the building blocks of proteins
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from which almost all cellular machinery
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is shaped
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[Music]
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to prove this back in the 1950s to
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American scientists Stanley Miller and
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Harold Urey designed a now famous
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experiment to try and create these amino
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acids from what they believed the
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composition of the early atmosphere to
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be they started with a mixture of water
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methane ammonia and hydrogen and ran an
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electric spark through that mixture on
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the early earth the same conditions
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could have been created by a lightning
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bolt
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spearing down from the thunder clouds
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that capped the first mountains the
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result was the creation of entirely new
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chemicals including several of the amino
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acid building blocks that all life on
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Earth uses they proved that organic
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molecules could in fact be made from
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inorganic matter so the building blocks
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existed as a kind of organic soup in
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Earth's early oceans but this alone is
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not life the molecules must come
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together in a very specific way to form
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self-replicating molecules and protein
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machinery the key to life and therein
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lies the paradox today almost all living
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things use DNA as their self-replicating
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molecule the patterns of nuclear bases
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in the molecule encode all the
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instructions for growing and reproducing
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and making proteins but of course 20v do
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these things it needs protein machinery
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to read the instructions interpret them
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and make new components it needs the
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hands to do the work
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so proteins are needed to read and
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reproduce the DNA but the DNA
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instructions are needed to make the
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proteins in the first place
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it's the ultimate conundrum the original
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chicken and egg what came first the
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proteins or DNA we are back at the
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beginning our primary problem the loop
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continues life baguettes life yet again
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yet the true answer is probably neither
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the DNA or the proteins scientists today
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think that another molecule bridge the
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gap the true prototype for the complex
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machinery that powers our existence the
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true beginning of life on earth beneath
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the churning chaos of Hadean Earth's
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deep oceans potentially for the first
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time a molecule successfully replicates
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itself
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[Music]
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our n a as it is known is a
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self-replicating single stranded
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molecule similar to but simpler than DNA
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it can replicate but it can also not
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itself up into 3d structures very
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similar to the protein machinery used in
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living things today scientists believe
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RNA could have been a catch-all molecule
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that performed all the functions of
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early metabolism and replication the
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result would have been what scientists
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call the RNA world where all of biology
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is made up of this single-stranded
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nuclear base pattern
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in the prebiotic soup random
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combinations of sugars and nuclear bases
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come together and are joined
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spontaneously by chemical reactions some
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break apart again but some stay stuck
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and continue to grow into long strands
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one nuclear base after another
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sometimes the Strand effects its own
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structure coiling or folding back in on
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itself in this way a kind of pre life
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natural selection takes hold to select
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the kinds of molecules that are
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structurally stable and mechanically
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useful the stable strands can act as
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templates for replication for making
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another identical to itself that the
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bunched up strands acting as rudimentary
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machines to help that replication along
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a whole ecosystem of different RNA
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molecules emerges proliferating and
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diversifying more stable strands
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replicating more successfully floating
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freely within the primordial soup
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[Music]
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but this too is not yet life
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the RNA ecosystem alone is a fluke of
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chemistry not a self-sustaining organism
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any chemical imbalances in the
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primordial oceans could have collapsed
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and destroyed the entire RNA world even
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the smallest puddle on the primordial
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earth is a big place for a fragile
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strand of RNA the chemicals needed for
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metabolic chemical reactions being
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impossibly diluted the chances of them
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running into each other are vanishingly
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small promising reactions all the while
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being disrupted by other chemicals
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floating around in the water so for
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metabolism to really get going
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the reactions needed a box to happen in
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separated from the outside environment
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where chemicals were concentrated and
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where the RNA could help direct the
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composition within all living things
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rely on these compartments these boxes
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some make do with just one others have
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trillions
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[Music]
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just like the machinery within the
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earliest cells probably looked very
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different to today modern cells have
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infinite variety and complexity but the
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earliest cells would have been much
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simpler but there's a good chance they
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were made of similar material called
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fatty acids these two would have formed
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spontaneously from chemical reactions in
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the prebiotic soup but it's their
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interaction with the surrounding water
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that makes them special fatty acids and
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the molecular relatives have a two part
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structure part is attracted to water
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while the other part is repelled by it
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so what does a fatty acid do when it
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finds itself immersed in water it cannot
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tear itself apart to satisfy both halves
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of its bi-polar nature instead it seeks
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solace in groups spontaneously
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self-organizing into spherical
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structures that shield the water heating
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portions while allowing the water loving
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parts to bathe in the soothing Wash
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fatty acids may not have been the most
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abundant molecule on the early Earth but
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their spontaneous self-organization
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makes them promising candidates for the
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earliest protocells larger spheres could
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easily have contained strands of
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replicating RNA the environment inside
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isolated and protected
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chemical reactions can happen in this
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new concentrated internal environment
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they can be influenced and directed by
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the RNA strands and the changes inside
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influence the strands themselves the
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first tentative metabolisms arise
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natural selection of chemical stability
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meaning that only those concoctions that
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favor self-preservation
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and perpetuation can stick around from
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starborn atoms and molecules
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concentrated on the young Earth's
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volatile surface giant macromolecules
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formed found ways to reproduce and pass
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their success on to new generations with
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survival the sole purpose in proving and
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warping along the way just this one time
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life arose spontaneously matter begat
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life allowing life to beget life for
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another three and a half billion years
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and counting
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next time we follow life back to its
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last Universal common ancestor and find
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out where on earth these first tentative
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steps into biology took place we'll
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explore the controversy around the very
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first fossils and consider the
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possibility that life itself may have
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been delivered from space
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you've been watching the entire history
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of the earth don't forget to Like
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the comments what you'd like to see
00:21:22
covered in the future thanks for
00:21:25
watching and we'll see you next time
