Time, Life and the Colonization of the Land
Time, Life and the Colonization of the Land. Time How do we fit God within the concept of time ? Like CS Lewis I believe we can not. There is much controversy between creationism and evolutionists but such a simple dichotomy is probably unnecessary if we consider a few basics. The Earth has undoubtedly been in creation for over 4 billion years. Man's ascent confined to at best a few million years but to dent the validity of Scripture based on these facts is absurd.
There is no dichotomy once we accept that God almost certainly exists outside of time and that the actual evolution of man is in itself hotly debated. In this chapter we will provide the temporal underpinning for the ten part discussion of the God and Nature series. We will look at the temporal frameworks as they stand, then some of the theories of how life originated and where life originated before moving on to the rise of man.
Time is a component of a measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify the motions of objects. Time has been a major subject of religion, philosophy and science but defining time in a noncontroversial manner applicable to all fields of study has consistently eluded the greatest scholars. Among prominent philosophers, there are two distinct viewpoints on time.
One view is that time is part of the fundamental structure of the universe a dimension in which events occur in sequence. Time travel, in this view, becomes a possibility as other "times" persist like frames of a film strip, spread out across the time line.Sir Isaac Newton subscribed to this realist view, and hence it is sometimes referred to as Newtonian time. The opposing view is that time does not refer to any kind of "container" that events and objects "move through", nor to any entity that "flows", but that it is instead part of a fundamental intellectual structure within which humans sequence and compare events.
This second view, in the tradition of Gottfried Leibniz and Immanuel Kant holds that time is neither an event nor a thing, and thus is not itself measurable nor can it be traveled. Temporal measurement has occupied scientists and was a prime motivation in navigation and astronomy. Periodic events and periodic motion have long served as standards for units of time. Examples include the apparent motion of the sun across the sky, the phases of the moon, the swing of a pendulum, and the beat of a heart. Currently, the international unit of time, the second, is defined in terms of radiation emitted by caesium atoms.
Time is also of significant social importance, having economic value - time is money - as well as personal value, due to an awareness of the limited time in each day and in human lifespans. It is necessary to consider the nature of time when considering the nature of God. Life The history of the Earth covers approximately 4.6. billion years (4,567,000,000 years), from Earth's formation out of the solar nebula to the present. This chapter presents a broad overview, summarizing the leading, most current scientific theories. The details of the origin of life are unknown, though the broad principles have been established. Two schools of thought regarding the origin of life have been proposed.
The first suggests that organic components may have arrived on Earth from space - Panspermia, while the other argues for terrestrial origins. The mechanisms by which life would initially arise are nevertheless held to be similar. There are several main theories of how life originated. Let us take these in rough chronological order. Firstly the theory of Panspermia. It was thought that micro-organisms had arrived on Earth from another part of the universe carried by meteorites or comets.
Secondly, since there was no real evidence for panspermia chemical theories of the origin of life arose and are more plausible at our current level of knowledge. Here the theory is that life arose from chemical reactions between organic molecules abiotically (not manufactured by organisms). Herman Muller felt that the first life forms must have been genes that replicated themselves and mutated allowing them to evolve. In 1923 Alexander Oparin hypothesized that over evolutionary time molecules within droplets of mixed oil/water became complex, with enzymes forming to organize other molecules into metabolic cycles. Genes would form later. JBS Haldane broadly agreed with this view. These ideas modified when scientists realised that genetic code in the form of DNA had to come first and an energy source such as sunlight or lightening was also probably needed.
In the 1950s Miller and Urey conducted experiments using flasks with chemicals as found in the early atmosphere, water and an electrical charge. Organic molecules were synthesized. This showed it was possible to synthesize organic molecules from ingredients found in the early history of the Earth. Later it became apparent that life may also have begun in the ocean depths fueled by hydrothermal vents. Hydrothermal vent systems develop at depths of several kilometers in the oceans in mid ocean spreading centres where there is hot upwelling lava. Sea water percolates and is vented back at hot temperatures, full of minerals, as either warm seeps, black or white "smokers".
There are many theories about how life may have originated around these vents and in fact these areas may even have been where photosynthesis first developed as there is a faint haze around these vents. The vent systems are highly dynamic and unstable environments but they do support over 200 species of life found so far. For more detail on vents see Harding and Starzynska "Deep Sea Environments" (2008). If life arose on Earth, the timing of this event is highly speculative—perhaps it arose around 4 billion years ago. In the energetic chemistry of early Earth, a molecule (or even something else) gained the ability to make copies of itself–the replicator. The nature of this molecule is unknown, its function having long since been superseded by life’s current replicator, DNA In making copies of itself, the replicator did not always perform accurately: some copies contained an “error.” If the change destroyed the copying ability of the molecule, there could be no more copies, and the line would “die out.” On the other hand, a few rare changes might make the molecule replicate faster or better: those “strains” would become more numerous and “successful.” As choice raw materials (“food”) became depleted, strains which could exploit different materials, or perhaps halt the progress of other strains and steal their resources, became more numerous.
Several different models have been proposed explaining how a replicator might have developed. Different replicators have been posited, including organic chemicals such as modern proteins, nucleic acids, phospholipids, crystals or even quantum systems. There is currently no method of determining which of these models, if any, closely fits the origin of life on Earth. One of the older theories, and one which has been worked out in some detail, will serve as an example of how this might occur. The high energy from volcanoes, lightning and ultraviolet radiation could help drive chemical reactions producing more complex molecules from simple compounds such as methane and ammonia. Among these were many of the relatively simple organic compounds that are the building blocks of life.
As the amount of this “organic soup” increased, different molecules reacted with one another. Sometimes more complex molecules would result—perhaps clay provided a framework to collect and concentrate organic material. The presence of certain molecules could speed up a chemical reaction. All this continued for a very long time, with reactions occurring more or less at random, until by chance there arose a new molecule: the replicator. This had the bizarre property of promoting the chemical reactions which produced a copy of itself, and evolution began properly. Other theories posit a different replicator.
In any case, DNA took over the function of the replicator at some point; all known life (with the exception of some viruses and prions) use DNA as their replicator, in an almost identical manner. Current evidence suggests that the last universal common ancestor lived during the early Archean eon, perhaps roughly 3.5 billion years ago or earlier. This “LUCA” cell is the ancestor of all cells and hence all life on Earth. It was probably a prokaryote, possessing a cell membrane and probably ribosomes, but lacking a nucleus or membrane-bound organelles such as mitochondria or chloroplasts. Like all modern cells, it used DNA as its genetic code, RNA for information transfer and protein synthesis, and enzymes to catalyze reactions. Some scientists believe that instead of a single organism being the last universal common ancestor, there were populations of organisms exchanging genes in lateral gene transfer. Estimates vary, but by about 3 billion years ago, something similar to modern photosynthesis had probably developed.
This made the sun’s energy available not only to autotrophs but also to the heterotrophs that consumed them. Photosynthesis used the plentiful carbon dioxide and water as raw materials and, with the energy of sunlight, produced energy-rich organic molecules (carbohydrates). Moreover, oxygen was produced as a waste product of photosynthesis. At first it became bound up with limestone, iron, and other minerals. There is substantial proof of this in iron-oxide rich layers in geological strata that correspond with this time period. The oceans would have turned to a green color while oxygen was reacting with minerals. When the reactions stopped, oxygen could finally enter the atmosphere. Though each cell only produced a minute amount of oxygen, the combined metabolism of many cells over a vast period of time transformed Earth’s atmosphere to its current state.
Among the oldest examples of oxygen-producing lifeforms are fossil Stromatolites. This, then, is Earth’s third atmosphere. Some of the oxygen was stimulated by incoming ultraviolet radiation to form ozone which collected in a layer near the upper part of the atmosphere. The ozone layer absorbed, and still absorbs, a significant amount of the ultraviolet radiation that once had passed through the atmosphere. It allowed cells to colonize the surface of the ocean and ultimately the land: without the ozone layer, ultraviolet radiation bombarding the surface would have caused unsustainable levels of mutation in exposed cells. Besides making large amounts of energy available to life-forms and blocking ultraviolet radiation, the effects of photosynthesis had a third, major, and world-changing impact. Oxygen was toxic; probably much life on Earth died out as its levels rose - the Oxygen Catastrophe. Resistant forms survived and thrived, and some developed the ability to use oxygen to enhance their metabolism and derive more energy from the same food.
Multicellularity Around 1.1 billion years ago, the supercontinent Rodinia was assembling. The plant, animal and fungi lines had all split, though they still existed as solitary cells. Some of these lived in colonies, and gradually some division of labour began to take place; for instance, cells on the periphery might have started to assume different roles from those in the interior. Although the division between a colony with specialized cells and a multicellular organism is not always clear, around 1 billion years ago, the first multicellular plants emerged, probably green algae.
Possibly by around 900 million years ago, true multicellularity had also evolved in animals. At first it probably somewhat resembled that of today’s sponges, where all cells were totipotent and a disrupted organism could reassemble itself. As the division of labor became more complete in all lines of multicellular organisms, cells became more specialized and more dependent on each other; isolated cells would die. Many scientists believe that a very severe ice age began around 770 million years ago, so severe that the surface of all the oceans completely froze - Snowball Earth. Eventually, after 20 million years, enough carbon dioxide escaped through volcanic outgassing that the resulting greenhouse effect raised global temperatures.
By around the same time, 750 million years ago, Rodinia began to break up. Colonization of the Land For most of Earth’s history, there were no multicellular organisms on land. Oxygen accumulation from photosynthesis resulted in the formation of an ozone layer that absorbed much of Sun’s ultraviolet radiation, meaning unicellular organisms that reached land were less likely to die, and prokaryotes began to multiply and become better adapted to survival out of the water. Prokaryotes had likely colonized the land as early as 2.6 billion years ago even before the origin of the eukaryotes. For a long time, the land remained barren of multicellular organisms.
The supercontinent Pannotia formed around 600 million years ago and then broke apart a short 50 million years later. Fish, the earliest vertebrates evolved in the oceans around 530 million years ago. A major extinction event occurred near the end of the Cambrian period, which ended 488 million years ago. In fact its worth mentioning radiations and extinctions in slightly more detail. Radiations are relatively rapid increases in the diversity of organisms. Extinctions are the decreases in the diversity of organisms.
The Cambrian explosion was the first major radiation that we can see from the limited fossil record. There have been five major mass extinctions that we can trace from the fossil record. These are in order the Late Ordovician, Late Devonian, Late Permian, Late Triassic and Late Cretaceous. All mass extinctions are associated with global climate changes and meteorite impacts may also have played their part. It should be stressed that the fossil records are far from complete and much research remains in this area. The Cambrian era contains the so called Cambrian explosion where life began to diversify at an extraordinary rate. In a relatively short period of geological time, over about 5 to 10 million years all the body plans of animals we know today evolved. We know this as we have evidence from the Burgess Shale fossil finds. This deposit was first discovered by Walcott and finds include animals such as Anomalocaris, Marella spledens and a range of trilobites.
The Cambrian was also the era in which the first shelled animals appear in the sea so is very significant. Several hundred million years ago, plants (probably resembling algae) and fungi started growing at the edges of the water, and then out of it. The oldest fossils of land fungi and plants date to 480–460 million years ago, though molecular evidence suggests the fungi may have colonized the land as early as 1000 million years ago and the plants 700 million years ago. Initially remaining close to the water’s edge, mutations and variations resulted in further colonization of this new environment.
The timing of the first animals to leave the oceans is not precisely known: the oldest clear evidence is of arthropods on land around 450 million years ago, perhaps thriving and becoming better adapted due to the vast food source provided by the terrestrial plants. There is also some unconfirmed evidence that arthropods may have appeared on land as early as 530 million years ago. At the end of the Ordovician period, 440 million years ago, additional extinction events occurred, perhaps due to a concurrent ice age. Around 380 to 375 million years ago, the first tetrapods evolved from fish. It is thought that perhaps fins evolved to become limbs which allowed the first tetrapods to lift their heads out of the water to breathe air. This would let them survive in oxygen-poor water or pursue small prey in shallow water. They may have later ventured on land for brief periods. Eventually, some of them became so well adapted to terrestrial life that they spent their adult lives on land, although they hatched in the water and returned to lay their eggs. This was the origin of the amphibians.
About 365 million years ago, another period of extinction occurred, perhaps as a result of global cooling. Plants evolved seeds, which dramatically accelerated their spread on land, around this time (by approximately 360 million years ago). Some 20 million years later (340 million years ago), the amniotic egg evolved, which could be laid on land, giving a survival advantage to tetrapod embryos. This resulted in the divergence of amniotes from amphibians. Another 30 million years (310 million years ago) saw the divergence of the synapsids (including mammals) from the sauropsids (including birds and non-avian, non-mammalian reptiles). Other groups of organisms continued to evolve and lines diverged—in fish, insects, bacteria, and so on—but less is known of the details. 300 million years ago, the most recent hypothesized supercontinent formed, called Pangea.
The most severe extinction event to date took place 250 million years ago, at the boundary of the Permian and Triassic periods; 95% of life on Earth died out, possibly due to the Siberian Traps volcanic event. The discovery of the Wikes Land Crater in Antarctica may suggest a connection with the Permian-Triassic extinction, but the age of that crater is not known. But life persevered, and around 230 million years ago, dinosaurs split off from their reptilian ancestors. An extinction event between the Triassic and Jurassic periods 200 million years ago spared many of the dinosaurs, and they soon became dominant among the vertebrates. Though some of the mammalian lines began to separate during this period, existing mammals were probably all small animals resembling shrews. By 180 million years ago, Pangea broke up into Laurasia and Gondwana. The boundary between avian and non-avian dinosaurs is not clear, but Archaeopteryx, traditionally considered one of the first birds, lived around 150 million years ago. The earliest evidence for the angiosperms evolving flowers is during the Cretaceous period, some 20 million years later (132 million years ago). We will be looking at the botanical world later in this series.
Competition with birds drove many pterosaurs to extinction, and the dinosaurs were probably already in decline for various reasons when, 65 million years ago, a 10-kilometer meteorite likely struck Earth just off the Yucatan Peninsula, ejecting vast quantities of particulate matter and vapor into the air that occluded sunlight, inhibiting photosynthesis. Most large animals, including the non-avian dinosaurs, became extinct marking the end of the Cretaceous period and Mesozoic era. Thereafter, in the Paleocene epoch, mammals rapidly diversified, grew larger, and became the dominant vertebrates.
Perhaps a couple of million years later (around 63 million years ago), the last common ancestor of primates lived. By the late Eocene epoch, 34 million years ago, some terrestrial mammals had returned to the oceans to become animals such as Basilosaurus which later gave rise to dolphins and whales. We shall be taking a look at the Ocean environment later in the series but let us turn now to a discussion of the rise of man.
Dr Simon Harding and Lidia Starzynska
www.biblon.com
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