![\"Goddard's](\"https:\/\/wp-media.patheos.com\/blogs\/sites\/186\/2017\/03\/BENNU%E2%80%99S_JOURNEY_-_Early_Earth.jpg\")
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Current estimates of the age of the Earth put it at about 4.543 billion years.<\/p>\n
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That makes this find potentially\u00a0stunning:<\/p>\n
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https:\/\/arstechnica.com\/science\/2017\/03\/3-7-billion-year-old-fossils-evidence-of-ancient-bacteria-in-ancient-rocks\/<\/a><\/p>\n \u00a0<\/p>\n If the discovery isn\u2019t overturned \u2014 has anybody seen anything to overturn it? \u2014 the biology\u00a0on our planet is at least\u00a03.77 billion years old, and it\u00a0could<\/em>\u00a0even be as old as 4.28 billion years.<\/p>\n \u00a0<\/p>\n That means that organic life was underway on Earth within no more than 773 million years of Earth\u2019s earliest existence \u2014 and perhaps within as little as 263 million years. \u00a0In other words, it appeared just about as soon as it possibly could. \u00a0And there\u2019s no reason to believe that scientists have found the absolutely earliest organisms ever to have lived here. \u00a0The odds are extraordinarily low that, by sheer dumb luck, out of all the geological materials that have been submerged beneath the seas or have\u00a0been folded underneath tectonic plates or now happen to rest upon Earth\u2019s surface \u2014 \u00a0scientists happen to have found\u00a0the very first living things.<\/p>\n \u00a0<\/p>\n But what, exactly, does it mean to say that the Earth is about 4.543 billion years old? \u00a0Did it simply suddenly appear as a solid ball at that point, ready for the advent of giant Sequoias, lemurs, and Bernie Sanders?<\/p>\n \u00a0<\/p>\n Not even close.<\/p>\n \u00a0<\/p>\n Remember that, according to current scientific consensus, the Earth came into being in the same fashion that most if not all other objects in our solar system did, as a solidified cloud of dust particles and gases remaining as \u201cleft overs\u201d from the same process that formed the Sun. \u00a0Probably the remnants of an exploded supernova, or of more than one, these gases and particles coalesced into planets, asteroids, and comets because of mutual and ever increasing gravitational attraction. \u00a0For maybe half a billion years, the interior of the planetesimal or protoplanet that would become Earth remained\u00a0solid and (relatively) cool, perhaps at a balmy temperature of approximately 2,000\u00b0F.<\/p>\n \u00a0<\/p>\n I say \u201crelatively cool\u201d because, by contrast, when the Sun shrank in upon itself by a process of gravitational compaction it began the steady nuclear fusion that continues today, radiating heat and light and (ultimately) making our lives possible. \u00a0But our future home would have been hot, even molten, because the solar system wasn\u2019t yet the rather orderly place with distinct planets and clear orbits that it would eventually become. \u00a0For a long time, large and ever growing planetesimals were colliding and merging with each other, and such collisions \u2014 creating friction on an inconceivably massive scale \u2014 generated enormous heat.<\/p>\n \u00a0<\/p>\n This is what is called the \u201cHadean\u201d period of Earth\u2019s history \u2014 running from roughly 4.6 billion to 4 billion years before the present. \u00a0(The term Hadean<\/em> comes, as you might have guessed, from the Greek noun Hades<\/em>, which, in this case, signifies Hell<\/em>. \u00a0Not a bad description, as you will see.) \u00a0In a sense, the Hadean period wasn\u2019t really a geological period at all, because, with the exception of meteorites (which are, by definition, extraterrestrial), no rocks ever found on our planet are so old. \u00a0In fact, some scientists use an altogether different term to refer to the earliest stages of Earth\u2019s history, calling our protoplanet \u201cGaia\u201d in order to distinguish from the solid planet that it eventually became.<\/p>\n \u00a0<\/p>\n The oldest meteoric rocks that have been discovered are currently dated \u2014 apart from the fascinating \u201cHypatia\u201d stone, which deserves its own discussion \u2014 to between 4.5 and 4.6 billion years ago. \u00a0The oldest lunar rock thus far dated has been placed at about 4.44 billion years of age. \u00a0(Although the Moon is derivative of the Earth and thus offers some clues to our planet\u2019s formation, it doesn\u2019t experience plate tectonics and, with neither water nor an atmosphere, it doesn\u2019t experience erosion, either.\u00a0 So ancient lunar rocks don\u2019t disappear. \u00a0Unless astronauts take them.)<\/p>\n \u00a0<\/p>\n But these conditions couldn\u2019t (and didn\u2019t) last forever. \u00a0The main components of the Earth\u2019s interior in that epoch, according to currently available evidence and theory, were iron and various silicates \u2014 that is, salts combining silicon and oxygen. \u00a0But there were also small amounts of other elements, including some (notably uranium, thorium, and potassium) that were radioactive. \u00a0It is the\u00a0relative abundance of these heavier elements in the early Earth and in our solar system more generally that points to their origin in one or more supernovas, since such heavier elements, otherwise rather uncommon in the universe as a whole, are produced by stellar nuclear fusion. \u00a0By mass, only about 2% of our galaxy is composed of \u201cheavy elements\u201d \u2014 that is, of elements other than hydrogen and helium. \u00a0Those two \u201clight elements\u201d represent an astonishing 74% and 24%, respectively, of all of the baryonic matter in the universe. \u00a0And baryonic matter, we should recall, represents only about 4.6% of the universe\u2019s total energy, which is otherwise composed of dark energy (74%) and dark matter (24%).) \u00a0(For a reflection on this subject from quite another angle, see my 2015 Deseret News<\/em> column \u201cMaterialism isn\u2019t what it used to be.\u201d<\/a>)<\/p>\n \u00a0<\/p>\n As millions of years passed, energy released from those elements by slow radioactive decay gradually heated the Earth, melting some of its constituent materials. \u00a0The iron melted before the silicates could and, because it was heavier, it naturally sank toward the center. \u00a0In turn, this forced the lighter silicates that its descent displaced to rise up toward the proto-planetary surface. \u00a0After many years, that slowly sinking and coalescing iron reached the center of the still-forming planet \u2014 and attained stability \u2014 at almost 4,000 miles from the surface. \u00a0Finally, enough iron accumulated at the Earth\u2019s center to become our planet\u2019s core, more or less as we know it today. \u00a0Gravitation now kept it in place, because, obviously, to move further would be to move upward<\/em>.<\/p>\n \u00a0<\/p>\n By contrast, the face of the Earth was still turbulent and unstable<\/em>\u2014suffering (as it were) gigantic earthquakes and even occasional sheer liquid bubbling, like simmering oatmeal. \u00a0Erupting volcanos pocked the Earth, and flowing lava covered virtually all of it. \u00a0Moreover, because the Earth\u2019s protective atmosphere hadn\u2019t yet come into existence, solar rays baked its outer surface and meteors frequently bombarded it. \u00a0Hadean<\/em> seems a pretty apt adjective to describe this period.<\/p>\n \u00a0<\/p>\n But the Earth inevitably began to cool, as everything in the universe is naturally fated to do, and a thin but (again) fairly stable crust of solid rock formed (as, again, sometimes happens with oatmeal). \u00a0The oldest terrestrial rocks currently known to scientists date to roughly 3.8 billion years before the present. \u00a0It\u2019s probable that rocks existed on Earth prior to this, but hard evidence for them \u2014 pardon the pun! \u2014 may never actually be found, partly because most really old things aren\u2019t found but mostly because any older rocks have likely been destroyed by erosion and the constant recycling of materials caused by plate tectonics and its perpetual subductions.<\/p>\n \u00a0<\/p>\n With the advent of solid terrestrial rock, perhaps somewhat prior to our oldest evidence from 3.8 billion years ago, the geological history of Earth properly began. \u00a0This is what is called\u00a0the \u201cArchaean eon.\u201d<\/p>\n \u00a0<\/p>\n Of course, the new, hard terrestrial crust wasn\u2019t perfectly smooth. \u00a0There were depressions (and elevations) in it. \u00a0These formed\u00a0natural basins. \u00a0Meanwhile, water was rising from the interior of the planet through fissures and via volcanic eruptions, as well as being delivered by meteorites, and that water collected to form Earth\u2019s primordial seas.<\/p>\n \u00a0<\/p>\n