The First Six Days
Page 4
It is of interest to note that all living cells present today (including our own cells) have an unbroken chain of cell division and growth stretching all the way back to the original protocell formed during biogenesis, every living organism’s common ancestor. The chemical conditions of the early Earth were capable of producing organic chemicals required for the first protocell development. The Miller-Urey experiment confirmed this hypothesis by producing some of the organic components of life, from an atmosphere of methane, ammonia and water vapour.
It is of interest to note that the phrase from the fourth day “let the waters bring forth” is explained by Rabbi Chaim ben Attar in his commentary (Or HaChaim) to mean that Hashem gave the seas the power to produce living organisms (swarming creatures) initially, until they received the blessing from Hashem to “be fruitful and multiply”. This statement is made on the fifth day as the Torah’s description is of bringing forth complex swarming creatures and not single-celled organisms that cannot be seen by the naked eye. But since the seas were created on the third day there was a period of time before they had the potential to develop more complex and larger eukaryotic organisms. This did not occur until the Cambrian era 545 million years ago, correspondingly the fifth day.
All matter in the universe erupted from a single event, the Big bang. It seems that all life on the earth also erupted from a single common ancestor during biogenesis.
Eukaryotic cells began to evolve into macroscopic organisms, the first of its kind 2.1 billion years ago. Several types of fossil appear to represent simple multi cellular forms of life found by the end of the Paleoproterozoic. Fossils known as carbon films, small dark compressions resemble circles, ribbons or leaves and some may resemble seaweed and algae. So the first multicellular organisms were the simple plant life that evolved. Even up until the early Devonian period the vegetation consisted of primarily small plants, the tallest predicted to be a metre tall.
Ramban explains the use of the term desheh eisev in naming the plants is related to the verb ÓéÐ (desheh), "to let the earth sprout". This verb refers to small underdeveloped plants and can apply to trees also, possibly indicating that all plants at this time were small and underdeveloped.
"A recent Nature article by Kevin Zahnle concludes that the sulphur isotopes in sedimentary rocks indicate that the photochemistry of the atmosphere altered dramatically 2.46 billion years ago, and that a major green house gas, probably methane had been removed3. In Zahnle's model, the action of ultra-violet light on methane produces a high-altitude hydrocarbon haze akin to the photochemical smog that shrouds Saturn's moon Titan. Zahnle states that "life 2.5 billion years ago seems to have existed under dusty yellow skies"."
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1Bereishis rabbah (17:5)
2Bereshis Raba 3:7
3 Zahnle, K. Nature, Vol 454 p41-42. 03-07-08
Day 4
“Hashem said ‘Let there be luminaries in the firmament of the heaven to make a distinction between night and day……and let them be for signs, for seasons’.”
The ancient rise of atmospheric oxygen is of great interest due to its close relationship with evolution. The consensus among the scientific community is that atmospheric oxygen first reached appreciable levels around 2.4 billion years ago1, an event known as the great oxidation event (GOE). The evidence for the GOE was partly from the discovery that minerals in ancient rocks had unusual ratios of sulphur isotopes, a phenomenon known as mass-independent fractionation2 (MIF). The only mechanism that can produce this effect is the break down of sulphur dioxide by ultraviolet light in a low oxygen atmosphere. The MIF isotopic signature is absent or very small in rocks younger than 2.4 billion years, showing that the Earth’s atmosphere has been oxygen-rich since that time. One would expect that oxygen levels would rise when photosynthetic (oxygen-producing) bacteria evolved 2.7 billion years ago, 0.3 billion years before the GOE. Therefore there was a large time period between the appearance of photosynthetic organisms and the accumulation of oxygen in the atmosphere. According to Goldblatt et al. once photosynthesis began, the atmosphere became bistable, it could exist in either a low or high oxygen state. This bistability results from variations in the rate of oxygen consumption as oxygen levels vary. For example in a low oxygen atmosphere, oxygen is rapidly consumed in an ultraviolet-catalysed reaction with methane. But with an increase in atmospheric oxygen follows an increase in ozone levels which blocks solar ultraviolet radiation and halts the breakdown of oxygen. Therefore the atmosphere delayed in a low oxygen state for a long time following the appearance of photosynthesis, even though oxygen levels were on the brink of increase.
This change in atmosphere from a reducing atmosphere to an oxidating (oxygen containing) atmosphere also changed how it interacted with light. The oxidating atmosphere, which is what we still have today, was transparent to light and it would have now been possible to see the sun, moon and stars from the perspective of the earth’s surface. In Bereshis it is stated that the importance of the luminaries and stars is for signs and for seasons. Therefore what is important is not the initial creation of them but the revealing of them on earth. Their revealing, including that of the sun and moon, would have occurred when the atmosphere changed from opaque to transparent.
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1Cloud, P.E. Am. J. Sci. 1972
2Farquhar, J. et al. Science 2000
Day 5
“Hashem said ‘let the waters bring forth swarming creatures with live souls and fowl that will fly over the earth’.”
Ramban explains that the word sheretz used in Bereshis refers to creeping creatures such as flies among flying creatures. A flying sheretz refers to any flying creature with four or more legs, definitely not birds. Among sheratzim (crawling creatures) examples include ants, worms and fish. These creatures are called sheratzim because of their seemingly constant motion. The word sheratz is a compound from the words Úå éÔÀÐ (shehoo ratz) “that which runs”. Rashi also lists animals that are included in sheratzim, including ants, beetles, worms and fish.
Ramban also explains that the origin of the sheratzim was in the water and therefore the utterance concerning them was on the fifth day with the other sea creatures and not on the sixth day.
There next phrase concerning “fowl that will fly over the earth” is more difficult to reconcile, since there appears to be little commentary on the subject of the fowl. The Hebrew word used is “oph” which literally just means flying creature. An example of this is in Leviticus1, which uses the term “sheretz ha-oph” meaning creeping creature that flies, therefore oph can be used to describe any flying creature.
Ramban states that the phrase “and fowl will fly about” is a direct continuation of the previous phrase meaning that these flying creatures are directly connected to the sheratzim in the previous few words. Also in the Gemara2 a number of sages maintain that the “fowl” were created from both water and ground, possibly signifying that these creatures began to colonise the land.
The term oph could also be applied to birds but it states later in Bereshis3 that “Hasham formed out of the ground every beast of the field and every bird of the sky” signifying that the birds were created out of the ground on the sixth day with the rest of the animals. Therefore the “fowl” described here on the fifth day must indicate flying sheratzim or flying invertebrates (flying insects).
The Cambrian period was a time when the major groups of animals first appeared in the fossil record, known as the Cambrian explosion because of the relatively short time this diversity occurred. Many invertebrates evolved at this time in the oceans: a few examples are the trilobites, archaeocyathids, hyolithids and most other shelled organisms. These invertebrates bear a remarkable resemblance to the sheratzim described by Ramban that have a constant crawling motion.
Primitive fish appear in the Ordovician period between 510 to 445 millions years ago, a period best known for its diverse marine invertebrates. The earth underwent considerable changes during the Silurian period 443
to 417 million years ago. These include stabilisation of the climate and rise in sea levels, which had important repercussions for life. There is evidence for animal life on land for the first time, including the relatives of spiders and centipedes. Only invertebrates were present on the land at this point, the vertebrates (fish) were still in the ocean.
We have the same array of organisms described in Bereshis as is scientifically accepted at this time of evolution. Also the organisms are described as coming from the “waters” or oceans, agreeing with the accepted scientific view that life originated in the oceans and then migrated onto land.
Ramban separates the definition of a soul of vegetation and a soul of creatures. Ramban states “The soul of a mobile organism is classed as a living soul and there is such a thing as a soul that does not have life in it, that soul is of vegetation”. This idea shows a progression of life from an inert organism such as plants to a more mobile and active organism such as the invertebrates and vertebrates. This idea is the running basis of evolution, a progression and advancement of life forms to more complicated, adaptable and able species.
“And Hashem created the great sea-giants and every living being that creeps, which the waters brought forth after their kinds and all the winged fowl of every kind…Hashem blessed them saying ‘Be fruitful and multiply and fill the waters in the seas, but the fowl shall increase on the earth’.”
Ramban identifies the great sea giants as the leviathan, scripture does not say of them “and it was so” for they did not continue to exist.
By the mid-Devonian period, placoderms, the first “jawed” fish, appear. Many of these grew to very large sizes and were fearsome predators. The evolutionary history of placoderms has been compared to a brilliant light bulb that soon burns out. They were a highly successful and diverse taxon, but they lasted only about fifty million years. Placoderms bore heavy bony armour on the head and neck. Bony plates associated with the jaws performed the function of teeth, sometimes forming razor-like, literally self-sharpening edges.
However, placoderms reached their greatest diversity in the Devonian, the so-called "Age of Fishes". The Devonian saw the greatest diversity of a large number of fish taxa, including not only placoderms, but armoured jawless fishes, early Chondrichthyes, and the first ray-finned and lobe-finned fishes. Many of these taxa died out around the end of the Devonian Period for reasons that are still not well understood. Placoderms survived until the very end of the Devonian, and their extinction appears to have been quite sudden, but its causes are still unknown. One of the largest placoderms was Dunkleosteus, which reached estimated sizes of up to thirty feet (ten meters) in length. This makes Dunkleosteus and related species among the largest animals, of any kind, in the Devonian era.
Of great interest in the Devonian period is the rise of the first sarcopterygiians or lobe-finned fish. These eventually evolved into the first tetrapods (four legged animals) before the end of the Devonian. Ramban also goes on to discuss the blessing from Hasham. The creatures required the blessing in order that they should multiply greatly, whereas the plants did not need a specific blessing for reproduction as they sprouted up over the entire face of the earth.
We discussed the type of plant life that occurred during the Devonian in Chapter 4 (day 4) and would like to follow this with ideas of plant growth at this time. The early Devonian terrestrial vegetation had begun to spread, yet these plants did not have roots or leaves and many had no vascular tissue at all, unlike today’s plants. They probably spread largely by vegetative growth and did not grow more than a few centimetres tall. The early fauna living among these plants were primarily arthropods, mites, trigonatarbids, wingless insects and myriapods. The first winged insect fossils appeared just after the Devonian in the early Carboniferous period.
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1Leviticus (11:21)
2Talmud Chullin 27b
3Genesis (Bereshis) (2:19)
Day 6
“Let the earth bring forth creatures with live souls, each according to its kind, animals, and moving creatures, and beasts of the land each according to its kind. And it was so. Hashem made the beasts of the earth according to their kind and the animals according to their kind and all the treading creatures of the ground according to their kind.”
Ramban elucidates that ‘animals’ refer to herbivores and ‘beasts’ of the land are carnivores.
The Carboniferous period of the late Paleozoic era was 354 to 290 million years ago. Several major biological events occurred during this time. One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed for exploitation of land by certain tetrapods. The amniote egg allowed the ancestors of birds, mammals and reptiles to reproduce on land by preventing the desiccation (drying out) of the embryo inside.
Earliest amniote fossil was from the lizardlike Hylonomus, and other fossils indicate that basal tetrapods became more diverse during the Carboniferous. Fish-like bodies were replaced by large predators with long snouts, short sprawling limbs and flattened heads, such as temnospondyls. Anthracosaurs (basal tetrapods and amniotes with deep skulls) appeared and were quickly followed by diapsids, which divided into two groups: the marine reptiles, lizards and snakes versus the archosaurs (crocodiles, dinosaurs and birds).
The Permian period (290 to 248 million years ago) consists of the largest mass extinction recorded in history, causing the disappearance of most marine invertebrates. On land a relatively smaller extinction of diapsids (reptiles) and synapsids (mammals and mammal-like reptiles) cleared the way for other forms to dominate, leading to the “age of the dinosaurs”.
The Jurassic period of 210 to 70 millions years ago saw the origination of birds including Archaeopteryx, probably from Coelurosaurian ancestors. Also the first mammals evolved which were no bigger than rats. One of the most famous extinctions occurred at the end of the Cretaceous, the Cretaceous-Tertiary extinction 65 million years ago. Many theories have postulated what wiped out the dinosaurs, the most popular is a meteor impact that would have thrown billions of tonnes of dust into the atmosphere, blocking the sun’s light and cooling the planet. Whatever the reason, this mass extinction marked the end of the dinosaurs and brought in the age of the mammals.
The Paleocene era of 54.8 to 33.7 million years ago saw the introduction of the most modern order of mammals, all under 10kg in weight. The first very large mammals appeared in the Oligocene 33.7 to 23.8 million years ago such as elephants and horses. The Miocene period was a time of warmer global climates and the overall pattern of biological change for the Miocene is one of expanding open vegetation systems (such as deserts, tundra and grass lands) at the expense of diminishing closed vegetation (such as forests). This led to a rediversification of temperate ecosystems and many morphological changes in mammals and birds.
The Pliocene was a time of global cooling and drying caused by the accumulation of ice at the poles, contributing to the enormous spread of grasslands and savannas. This allowed the rise of the longlegged grazers which exist to this current day. The Pleistocene (1.8 million to 10,000 years ago) saw the rise of the large land mammals such as the mammoth, mastodons, long-horned bison and sabre-toothed cats. Also during the Pleistocene era a hominid species called Homo erectus (upright man) appeared which is believed to be the ancestor of modern humans. H. erectus originally migrated during the Pleistocene glacial period in Africa roughly 2.0 million years ago and so dispersed throughout various areas of the Old World. Fossilized remains dating 1.8 and 1 million year old have been found in India, China and Indonesia. H. erectus remains an important hominine since it is believed to be the oldest representation of early human migration. However, recent discoveries and analysis indicate that H. erectus’s situation on the human evolutionary tree may be phylogenetically akin to H. neanderthalensis, in that its lineage did not give rise to later variants of H. sapiens.
The lineage which gives rise to modern humans is still very much hotly debated in anthropology, but the genetic e
volution of humans has only been studied relatively recently. This genetic information has come from two primary sources, the mitochondrial DNA and the Y chromosome.
Mitochondrial genes are not inherited by the same mechanism as nuclear genes. At fertilization of an egg by a sperm, the egg nucleus and sperm nucleus each contribute equally to the genetic makeup of the zygote nucleus. In contrast, the mitochondria, and therefore the mitochondrial DNA, usually comes from the egg only. Therefore mitochondrial DNA is only passed through the maternal line.
Studies of sample populations across the globe have discovered that everyone has originated from one female called “Mitochondrial Eve”. This is the name given by researchers to the woman who is the matrilineal most recent common ancestor for all living humans, from whom all mitochondrial DNA (mtDNA) in living humans is descended. Mitochondrial Eve is the female counterpart of the Y-chromosomal Adam, the patrilinear most recent common ancestor.
She is believed by some to have lived about 150,000 years ago in what is now Ethiopia, Kenya or Tanzania. Her age is calculated based on the molecular clock technique of correlating elapsed time with observed genetic drift.
The concept of the molecular clock originated in the early 1960s and has since been used widely, more as a result of its downright usefulness than its biological accuracy, as it is clear that rates of evolution can and do vary considerably among species. Evolutionary rates depend on a combination of factors: generation time, population size, metabolic rate, the efficacy of DNA repair, and the degree to which mutations are beneficial or deleterious, all of which may vary among species. As the geneticist Steve Jones recently remarked, evolutionary biologists seem to use the molecular clock “with our fingers crossed”1.