In all past ages people have suffered from wrong ideas about the nature of the world, often mistaking speculation for fact. The wrong ideas were often passionately defended, until eventually, with the arrival of new facts, they came to be overturned and replaced. The idea of an Earth-centered universe was the order of the day for the astronomer-poet Omar Khayyam in eleventh century Persia. Geocentric cosmology—placing Earth at the center of things—prevailed throughout Europe from the time of The Rubayyat well into the Elizabethan era. The slow process of demoting Earth from the center of things began at the beginning of the sixteenth century. The Copernican revolution—beginning with publication by Copernicus of De Revolutionibus Orbium Celestium in 1543, progressing through the trial of Galileo Galilei, and culminating in the efforts of Tycho Brahe, Kepler, and Newton—finally removed the Earth from its privileged position of centrality in the solar system. This trend in which our place in the cosmos became diminished continued with advances in astronomy through the nineteenth, twentieth, and twenty-first centuries. Newer and more powerful telescopes and equipment, combined with deployment of spacecraft, continue to contribute to this process. We now know that our solar system is one of hundreds of billions of similar planetary systems in our Milky Way galaxy, which itself is one of a countless billions of galaxies in the observable universe.
The material of all earthly life, including us, is derived from atoms that owe their existence to cosmic processes. The carbon, oxygen, nitrogen, phosphorus, and metals in our bodies were all synthesized in the deep interiors of stars and were scattered into our midst by massive stars that exploded at the end of their lives—supernovae.
Current cosmological ideas about the grand structure of the universe favor a unique origin that is supposed to have taken place 13.8 billion years ago—the big bang theory. This theory owes its origins to Edwin Hubble’s discovery in the 1940s of an expanding universe—distant galaxies moving away from one another. From this discovery the idea developed that the entire universe started as a “point” at some instant of time in the past. After the lapse of 10-36 second following this “big bang” event 13.8 billion years ago, the universe, which was then still smaller than a single atom, is supposed to have undergone an episode of “inflation” lasting for some 10-33 seconds. “Quantum fluctuations” in this submicroscopic universe are next posited to be amplified along with the expansion of the universe, so accounting for everything we observe—subatomic particles, atoms, clusters of galaxies, galaxies, stars, planets, and ourselves. And what was there before the big bang event 13.8 billion years ago? Of course nothing, and this is the question that is reckoned by some to be meaningless—because nothing existed before: not even time! Even the very concept of time may not have a meaning.
This is the so-called standard cosmological theory, elegantly crafted in mathematical formulation and widely supported by a vast and powerful scientific establishment. But for sure it is not cast in stone. It has to be admitted that a sizeable chunk of relevant ideas still occupy the realm of speculation, and societal and cultural constraints play a crucial role in defense of this model. Other, less popular but equally elegant, formulations involve models of the universe that are oscillating, with expansion successively followed by contraction, and possessing an essentially infinite age. It is interesting to note that some of these models are strikingly reminiscent of Vedantic cosmologies and the philosophies of India that predated the Christian era by many centuries. Likewise it must be admitted that the standard big-bang cosmology does indeed look very much like a modern rendering of the Judeo-Christian story of creation.
The modern trend to support the currently fashionable big-bang cosmology is likely to be as transient as were earlier arguments favoring a long sequence of other cosmologies. The medieval cosmology famously describing the world as a globe carried on the back of a white elephant standing on top of an infinite stack of turtles comes to mind. As mentioned at the outset, all earlier models of the world including the pre-Copernican Earth-centered cosmology were passionately defended, but they all turned out to be wrong. It seems likely that the currently favored big-bang cosmology will require serious revision in the fullness of time. Modern astronomical data on galaxies forming some four hundred million years (a twinkling of an eye!) after the big bang are beginning to strain the credibility of standard cosmologies. Moreover, we cannot but remain slightly uneasy with the current status quo where the age of the entire universe is scarcely three times the age of Earth. But let’s not tarry on such inconsequential details.
Let us next turn our attention to Earth, planets, and smaller things, knowledge about which is more certain. Recent studies have shown that the earliest evidence of microbial life on the Earth dates to a time some 4.1 billion years ago. Signatures of this early life are to be found as carbon isotope signatures in grains trapped within zircons that condensed when Earth’s surface was still molten hot and when comet and meteorite impacts were still frequent. This episode of intense meteorite bombardment, representing the last stages in the accumulation of Earth’s crust, was followed by a period of bombardment by cometary bolides from the outer solar system that would have lasted for a third of a billion years. It is such icy bodies that brought most of the water that formed Earth’s oceans. Evaporation of water from the oceans led to an atmosphere and a cloud cover beneath which microbial life that also came with the comets was able to thrive.
In addition to the eight planets in the solar system, there are tens of thousands of minor planets, planetoids or asteroids; and surrounding this entire system at a distance of a tenth of a light year from the sun, is a gigantic shell of comets—the so-called Oort cloud. Most of the asteroids orbit around the sun in a plane between the orbits of Mars and Jupiter in the solar system, but an important class of objects known as Trans-Neptunian or Kuiper-Belt objects have orbits that take them far beyond the orbit of Neptune. Over the past decade several comets and minor planets (e.g., Ceres and Pluto) have been examined at close range using instruments carried by spacecraft. We are finding that the distinction between comets and large class, minor planets—typified by Pluto and Ceres—is fast disappearing. Most of the comets that we see from time to time in the sky come from this cloud of comets when they get pushed by passing stars into highly elliptical orbits that bring them into the inner solar system.
There is also in our vicinity a vast number of small fragments of rock and ice that orbit the sun. When these objects enter Earth’s atmosphere, they are heated to incandescence; and the visible streak in the sky is recognized as a meteor. If such a piece survives to reach Earth’s surface, it is recognized as a meteorite.
Most of Earth’s early history as a planet from 2.4 billion years ago to 0.6 billion years ago was marked by an alternation from intense cold and almost total glaciation to greenhouse/hothouse conditions when tropical temperatures would have prevailed from pole to pole. The so-called Huronian glaciation, which is possibly the severest of ice ages on record, straddled the period from 2.4 to 2.3 billion years ago; and the last major glaciation event, the Cryogenian snowball Earth, persisted from 850 to 630 million years ago. In both these instances Earth was plunged into the deepest cold.
Life on Earth
Bacteria and other unicellular life-forms are the only life that existed on Earth for the first 2 billion years of its history. The record of such early life is found in accumulations of carbonate mineral including calcite and dolomite that are pointers to biology. From evidence of this kind, and more directly from the existence of stromatolites—layered sedimentary grains cemented by biofilm—it can be inferred that microorganisms existed throughout the first 3.5 billion years of Earth’s history. Such single-celled lifeforms were followed by a dramatic explosion of an extraordinarily wide range of multicelled life forms between 530 and 520 million years ago—the so-called Cambrian explosion. The fact that this happened with extreme suddenness, leaving no trace of any intermediate forms or stages of development leading to multi-cellularity, presents a continuing enigma for Earth-bound evolutionary theories.
Recent studies on the DNA sequencing of many life forms have shown that regulatory genes that determine cell function as well as morphology span a wide range of phyla; but why a particular set of genes conducive to cooperative behavior and multi-cellurality took 3.5 billion years to switch on, remains a puzzle. The neo-Darwinian idea that a succession of small changes caused by mutations and consequent innovations derived in situ and followed by natural selection—survival of the fittest—explains such sudden jumps, is not supported by the available data.
Some 40 million years after the Cambrian explosion of life, much of the newly evolved species fizzled out from the geological record and was replaced by an exceedingly rich assortment of brand-new flora during another sudden event known as the ‘Great Ordovician biodiversification’ event. This moment in time can arguably be regarded as the starting point of all the radiations of modern flora and fauna on Earth. Recent studies have thrown light on the likely extraterrestrial origin of the Ordovician event. In 2014 a group of Swedish scientists discovered a new class of meteorite that appears to have resulted from a gigantic collision in the asteroid belt precisely 470 million years ago, coinciding exactly with the timing of the Ordovician event. Similar events involving cometary and meteoritic interactions with Earth may, in our view, be responsible for later episodes of biodiversification as well as for a series of mass extinction events that punctuate the long history of terrestrial life.
Emergence of Hominids
Our own immediate line of descent, the hominids, are thought to have inhabited Eastern Africa five to seven million years ago. The first modern humans walked out of the jungles of Africa as hunter-gatherers 300,000 years ago when the total population may have been less than 1 million. By about 15,000 years ago, we have evidence from cave paintings showing animal shapes linked with constellations in the sky, bearing testimony to a burgeoning interest in the cosmos. Artists in more recent times have further pursued our links with the cosmos, as for instance in Paul Gaugin’s famous nineteenth century painting with the title, translated from French as: Where do we come from? What are we? Where are we going? These questions epitomize an unending human quest to understand our ultimate origins, a quest that continues to the present day. In 2017 we have perhaps a little more than a glimmer of the correct answers; but their fullest significance could well continue to elude us for centuries or millennia to come.
The nature of our existence as sentient humans was mostly shrouded in magic, mystery, and religion until the intervention of Charles Darwin in 1859. The publication in that year of Darwin’s On the Origins of Species met with violent opposition, particularly from the Church. In a debate that took place at the Oxford University Museum a few months after the Darwin book was published, Bishop Samuel Wilberforce is said to have famously asked Thomas Huxley, the geologist and Darwin’s friend, whether he claimed his descent was from a monkey on his grandfather’s or grandmother’s side! Whether this exchange really took place or not is largely irrelevant. But it cannot be denied that removing God from the story of creation caused great consternation. Many people felt at the time that they were robbed of the comforting sense of security they had enjoyed for so long in the illusory belief in an omniscient, all-powerful God.
Darwin’s theory of 1859 still remains the cornerstone of modern biology. The most recent studies on genome sequencing have established a genetic and biochemical unity of all life, with our own links traced back to simpler life forms extending all the way down to the humblest bacterium.
At the most rudimentary chemical level, life in all its varied shapes and forms involves the interaction between two groups of biochemicals—the nucleic acids and proteins. Each of these constitutes linked chains of simpler molecules, the arrangements of which carry information crucial for life. The nucleic acids (which are double stranded) are themselves constructed from a sugar (ribose) and a phosphate wrapped into a helical structure, with pairs of bases (adenine, guanine, thymine, and cytosine) straddling the double helix. The proteins contain about twenty-one, separate amino acids linked into folded chains of several hundred molecules in length. The myriads of possible arrangements of these twenty-seven or so basic chemical structures make for the enormously wide diversity of life.
Improbability of Life
The blueprint for all life from bacteria to plants and animals was discovered in the 1950s by Watson and Crick to reside in DNA—in particular in the precise arrangements of the nucleotides A, G, T, C that effectively code for proteins that in turn control cell function. In a series of books and articles published in collaboration with the late Sir Fred Hoyle, I have argued that the highly specific arrangements needed for the operation of living cells cannot be understood as arising from random processes. For the simplest bacterium (Mycoplasma genitalium) the probability that its few-hundred genes will be discovered by random shuffling of their amino-acid components gives a figure of 1 in 101,000 or smaller. Hoyle and I have compared such horrendous improbabilities to the odds against a “tornado blowing through a junkyard leading to self assembly of a BOEING 707 airplane.”
But how, when, and where did the first bacterial cell originate? With the successful completion of the Copernican revolution at the end of the sixteenth century, the importance of Earth as regards its physical placement in the cosmos diminished. However, the Earth’s supremacy in regard to life and our own existence lingered well into the twentieth century. The idea of life originating in a primordial soup on Earth was first proposed by Haldane and Oparin in the early part of the twentieth century, and this point of view gained support throughout the latter part of the century.
The idea of an Earth-based primordial soup is now beginning to wear exceedingly thin with the arrival of new evidence from many directions. We have already mentioned that the oldest evidence of life on Earth dates back to 4.1 billion years ago, which is perhaps the first moment in Earth’s history when life could have survived. The window of opportunity for a primordial soup, therefore, appears to be pretty well squeezed out of the geological record. The emerging paradigm is of comets and meteorites that predated Earth introducing life in a fully-fledged genetic form from 4.1 billion years ago. The blueprint for all life embracing every future contingency and possibility may have predated the solar system by billions of years and may even be in some way an intrinsic property of the universe. This implies an element of teleology—meaning that the shape of life and things to come are in some way already predetermined. Some readers may find this point of view culturally or philosophically unacceptable. But the universe is the way it is and cannot be constrained by social or cultural prejudice.
The above is an edited excerpt, offered here with the publisher’s permission, from Cosmic Womb: The Seeding of Planet Earth by Chandra Wickramasinghe, Ph.D., and Robert Bauval (Bear & Company/Inner Traditions/Simon & Schuster, 2017). Dr. Wickramasinghe is director of the Center for Astrobiology at the University Buckingham in the U.K. and editor-in-chief of The Journal of Astrobiology.