The evolution of the biosphere
The process of the origin and evolution of living organisms is indivisible from the process of the origin and evolution of biosphere, the global planetary system. The origin of earthly life and the origin of the biosphere are aspects of a whole indivisible process.
Since the evolution of the biosphere is closely related to the evolution of other geospheres of planet Earth, it is advisable to consider this issue in the aspect of geochronology of the Earth.Earth's surface is a complex mosaic of exposures of different rock types that are assembled in an astonishing array of geometries and sequences. Individual rocks in the myriad of rock outcroppings (or in some instances shallow subsurface occurrences) contain certain materials or mineralogical information that can provide insight as to their “age.”
For years investigators determined the relative ages of sedimentary rock strata on the basis of their positions in an outcrop and their fossil content. According to the long-standing principle of the geosciences, that of superposition, the oldest layer within a sequence of strata is at the base and the layers are progressively younger with ascending order. The relative ages of the rock strata deduced in this manner can be corroborated and at times refined by the examination of the fossil forms present. The tracing and matching of the fossil content of separate rock outcrops (i.e., correlation) eventually enabled investigators to integrate rock sequences in many areas of the world and construct a relative geologic time scale.
Some estimates suggest that as much as 70 percent of all rocks outcropping from the Earth's surface are sedimentary. Preserved in these rocks is the complex record of the many transgressions and regressions of the sea, as well as the fossil remains or other indications of now extinct organisms and the petrified sands and gravels of ancient beaches, sand dunes, and rivers.
The geologic time scale is the “calendar” for events in Earth history. It subdivides all time into named units of abstract time called - in descending order of duration - eons, eras, periods, epochs, and ages. The enumeration of those geologic time units is based on stratigraphy, which is the correlation and classification of rock strata. The fossil forms that occur in the rocks provide the chief means of establishing a geologic time scale. One of the most widely used standard charts showing the relationships between the various intervals of geologic time is the International Chronostratigraphic Chart, which is maintained by the International Commission on Stratigraphy (ICS).
Because living things have undergone evolutionary changes over geologic time, particular kinds of organisms are characteristic of particular parts of the geologic record. By correlating the strata in which certain types of fossils are found, the geologic history of various regions - and of Earth as a whole - can be reconstructed. The relative geologic time scale developed from the fossil record has been numerically quantified by means of absolute dates obtained with radiometric dating methods.
1. The Precambrian is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is a supereon that is subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale.
1.1 Hadean began with the formation of the Earth about 4.6 billion years ago and ended, as defined by the ICS, 4 billion years ago.
1.2 Archean is one of the four geologic eons of Earth history, occurring 4,000 to 2,500 million years ago (4 to 2.5 billion years ago). There are four eras in the Archean: Eoarchean, Paleoarchean, Mesoarchean, Neoarchean. The Archean atmosphere to have nearly lacked free oxygen. Life in the Archean was limited to simple single-celled organisms (lacking nuclei), called Prokaryota. The first life forms and self-replicating RNA molecules evolve around 4,000 Ma, after the Late Heavy Bombardment ends on Earth.
Simple single-celled life (probably bacteria and archaea). First known oxygenproducing bacteria. First stromatolites (probably colonial cyanobacteria).1.3 Proterozoic is a geological eon representing the time just before the proliferation of complex life on Earth. The Proterozoic Eon extended from 2500 Ma to 541 Ma (million years ago), and is the most recent part of the Precambrian Supereon. It can be also described as the time range between the appearance of oxygen in Earth's atmosphere and the appearance of first complex life forms (like trilobites or corals). It is subdivided into three geologic eras (from oldest to youngest): the Paleoproterozoic, Mesoproterozoic, and Neoproterozoic. The first advanced single-celled, eukaryotes and multicellular life, Francevillian Group Fossils, roughly coincides with the start of the accumulation of free oxygen. This may have been due to an increase in the oxidized nitrates that eukaryotes use, as opposed to cyanobacteria. It was also during the Proterozoic that the first symbiotic relationships between mitochondria (found in nearly all eukaryotes) and chloroplasts (found in plants and some protists only) and their hosts evolved. The blossoming of
eukaryotes such as acritarchs did not preclude the expansion of
cyanobacteria; in fact, stromatolites reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1200 million years ago.
2. The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 541 million years to the present, and began with the Cambrian Period when diverse hard-shelled animals first appeared. The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which are further subdivided into 12 periods.
2.1 The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. It is the longest of the Phanerozoic eras, lasting from 541 to 251.902 million years ago, and is subdivided into six geologic periods (from oldest to youngest): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.
The Paleozoic was a time of dramatic geological, climatic, and evolutionary change. During the early Paleozoic, the huge continent Gondwana (510 million years ago) formed or was forming. By mid-Paleozoic, the collision of North America and Europe produced the Acadian-Caledonian uplifts, and a subduction plate uplifted eastern Australia. By the late Paleozoic, continental collisions formed the supercontinent of Pangaea and resulted in some of the great mountain chains, including the Appalachians, Ural Mountains, and mountains of Tasmania. The Cambrian witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared. Fish, arthropods, amphibians, anapsids, synapsids, euryapsids, and diapsids all evolved during the Paleozoic. Life began in the ocean but eventually transitioned onto land, and by the late Paleozoic, it was dominated by various forms of organisms. Great forests of primitive plants covered the continents, many of which formed the coal beds of Europe and eastern North America. Towards the end of the era, large, sophisticated diapsids and synapsids were dominant and the first modern plants (conifers) appeared. The Paleozoic Era ended with the largest extinction event in the history of Earth, the Permian-Triassic extinction event. The effects of this catastrophe were so devastating that it took life on land 30 million years into the Mesozoic Era to recover. Recovery of life in the sea may have been much faster.2.2 The Mesozoic Era is an interval of geological time from about 252 to 66 million years ago. This Era is also called the Age of Reptiles and the Age of Conifers. The era is subdivided into three major periods: the Triassic, Jurassic, and Cretaceous, which are further subdivided into a number of epochs and stages.
The era began in the wake of the Permian-Triassic extinction event, the largest well-documented mass extinction in Earth's history, and ended with the Cretaceous-Paleogene extinction event, another mass extinction which is known for having killed off non-avian dinosaurs, as well as other plant and animal species.
The Mesozoic was the time of significant tectonic, climate and evolutionary activity. The era witnessed the gradual rifting of the supercontinent Pangaea into separate landmasses that would eventually move into their current positions. The climate of the Mesozoic was varied, alternating between warming and cooling periods. Overall, however, the Earth was hotter than it is today. Dinosaurs appeared in the Late Triassic and became the dominant terrestrial vertebrates early in the Jurassic, occupying this position for about 135 million years until their demise at the end of the Cretaceous. Birds first appeared in the Jurassic, having evolved from a branch of theropod dinosaurs. The first mammals also appeared during the Mesozoic, but would remain small - less than 15 kg (33 lb) - until the Cenozoic.2.3 The Cenozoic Era is the current geological era, covering the period from 66 million years ago to the present day. The Cenozoic is also known as the Age of Mammals, because of the large mammals that dominate it. The continents also moved into their current positions during this era. The Cenozoic is divided into three periods: the Paleogene, Neogene, and Quaternary; and seven epochs: the Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, and Holocene. Early in the Cenozoic the planet was dominated by relatively small fauna, including small mammals, birds, reptiles, and amphibians.
From a geological perspective, it did not take long for mammals and birds to greatly diversify in the absence of the dinosaurs that had dominated during the Mesozoic. Mammals came to occupy almost every available niche (both marine and terrestrial), and some also grew very large, attaining sizes not seen in most of today's terrestrial mammals. Early animals were the Entelodon (the so-called "hell pig"), Paraceratherium (a hornless rhinoceros relative) and Basilosaurus (an early whale). The extinction of many large diapsid groups, such as flightless dinosaurs, Plesiosauria and Pterosauria allowed mammals and birds to greatly diversify and become the world's predominant fauna.
During the Cenozoic, mammals proliferated from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals, giving this period its other name, the Age of Mammals, despite the fact that there are more than twice as many bird species as mammal species.The Cenozoic is just as much the age of savannas, the age of codependent flowering plants and insects, and the age of birds. Grass also played a very important role in this era, shaping the evolution of the birds and mammals that fed on it. One group that diversified significantly in the Cenozoic as well was the snakes.
Evolving in the Cenozoic, the variety of snakes increased tremendously, resulting in many colubrids, following the evolution of their current primary prey source, the rodents.
The Cenozoic is full of mammals including chalicotheres, creodonts, whales, primates, entelodonts, saber-toothed cats, mastodons and mammoths, three-toed horses, giant rhinoceros like Indricotherium, the rhinoceroslike brontotheres, various bizarre groups of mammals from South America, such as the vaguely elephant-like pyrotheres and the dog-like marsupial relatives called borhyaenids and the monotremes and marsupials of Australia.
Many animals evolved including mammoths, giant ground sloths, dire wolves, saber-toothed cats, and most famously Homo sapiens. 100,000 years ago marked the end of one of the worst droughts in Africa, and led to the expansion of primitive humans. As the Pleistocene drew to close, major extinction wiped out much of the world's megafauna, including some of the hominid species, such as Neanderthals.
All recorded history and "the history of the world" lies within the boundaries of the Holocene epoch. Human activity is blamed for mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution. This is sometimes referred to as the "Sixth Extinction". Over 322 species have become extinct due to human activity since the Industrial Revolution.
Answer these questions:
1. Why is the biosphere described sometimes as «the fourth envelope»?
2. Where did life first develop? How?
3. What elements does the biosphere contain?
4. How important are the oceans for water cycling?
5. Decide whether these statements are true or false (T/F):
5.1 The biosphere is sphere of soils and rocks.
5.2 The ozone layer protects living beings from UV rays.
5.3 The deep ocean vent communities need sunlight for utilizing the chemistry of the hot volcanic vents.
5.4 At the ecosystem and biosphere levels, there is a continual recycling of carbon, nitrogen, oxygen and other elements, such as phosphorus, calcium, and potassium.
5.5 The process of photosynthesis releases carbon.
5.6 Glucose and other sugar molecules are concentrated in nectar and entice pollinators to aid plants in reproduction.
5.7 Water and carbon dioxide are the two constituents which cause the process of cellular respiration.