My Science School

The system of classifying living things was invented by a Swedish botanist called Carolos Linnaeus (1707-78). Latin was traditionally the language used by scholars, so the classifications have Latin names. This also means that living things can be identified by scientists in every country, no matter what the local name for a species might be.

Most plants and animals have popular names that can vary from place to place. So a name needed to be given that would be recognized everywhere. It was decided so use Latin for the scientific names, as it was the language use centuries ago by learned people. Carl Linnaeus was the man who established the modern scientific method for naming plants and animals. Scientific names are in two parts. The first part is the generic name, which describes a group of related living things. The second name is the specific name, which applies only to that living thing. This specific name may describe the living thing, or it could include the name of the person who discovered it.

Linnaeus and other scientists used Latin because it was a dead language. No people or nation uses it as an official language. Many other languages may have Latin bases but don't use all of it. So he would not insult any country when he began to name organisms although you will see that he did one time to a person he did not like. Before Linnaeus, species naming practices varied. He did study to be a doctor of medicine but was attracted to botany as many medicines at the time were from plants.

Many biologists gave the species they described long, unwieldy Latin names, which could be altered at will; a scientist comparing two descriptions of species might not be able to tell which organisms were being referred to. For instance, the common wild briar rose was referred to by different botanists as Rosa sylvestris inodora seu canina and as Rosa sylvestris alba cum rubore, folio glabro. The need for a workable naming system was made even greater by the huge number of plants and animals that were being brought back to Europe from Asia, Africa, and the Americas.

After experimenting with various alternatives, Linnaeus simplified naming immensely by designating one Latin name to indicate the genus, and one as a "shorthand" name for the species. The two names make up the binomial ("two names") species name. The sexual basis of Linnaeus's plant classification was controversial in its day; although easy to learn and use, it clearly did not give good results in many cases.

Some critics also attacked it for its sexually explicit nature: one opponent, botanist Johann Siegesbeck, called it "loathsome harlotry". (Linnaeus had his revenge, however; he named a small, useless European weed Siegesbeckia.)

The class of insects is the largest class of living things, containing over one million different species.

In terms of numbers of species, insects certainly represent the largest percentage of the world's organisms. There are more than 1 million species of insects that have been documented and studied by scientists. And the total number of documented species of living organisms at the present time is probably about 2.5 million. So insects represent about 40% of all known living species!

But that's not the end of the story. Scientists estimate that there may actually be somewhere between 10 and 30 million species of insects inhabiting our planet. So insects as a percentage of organisms might actually be greater than we currently estimate.

If we look at your question from the point of view of numbers of individuals, the answers is almost certainly insects as well. In fact, the answer may be ants. There are 14,000 known species of ants. And they all form ant colonies. In some species of ants, those colonies may be extremely large. One colony may contain many tens of thousands of individuals! Some scientists have made credible calculations suggesting that the weight of all ants is greater than that of all humans.

Lions are social animals that hunt and live in groups called prides. The males have little parental investment toward the cubs, and males may even commit infanticide against suckling cubs that are not their own. There is usually fierce competition for food because successful hunts are rare and members of the pride tend to gorge themselves when food is available. The ruling male lion will eat his fill, and then the other males, females, and finally the cubs. The competition for food contributes to the high mortality rate of the cubs.

The lion (Panthera leo) is the largest wild cat in Africa, yet populations of the 'king of the jungle' have dramatically declined by nearly half in just two decades. Historically lions occurred in sub-Saharan Africa as well as from northern Africa into southwest Asia and Europe. However only a remnant population remains in India and the present day populations only occur in sub-Saharan Africa.

Unique among all wild cats, lions have a social structure as opposed to a solitary lifestyle; and males differ from females with large manes, whereas males and females of other wild cats look very similar.

The scientific name for lion is Panthera leo which is also known as the lion binomial name, lion species name, lion latin name, lion biological name and lion zoological name. Some call it the lion botanical name however that term is applicable to the plant kingdom (botany) and not the animal kingdom (zoology).

Lions belong to the big cat genus Panthera and the full taxonomy or scientific classification of the lion species (Panthera leo) is as follows:

Lions belong to the:

Animal (Animalia) kingdom

Chordate (Chordata) phylum

Mammal (Mammalia) class

Carnivore (Carnivora) order

Cat (Felidae) family

Big cat (Panthera) genus

Lion (leo) species

The scientific name for lions is Panthera leo, the last two divisions.

Members of the monerans and protist families are the simplest organisms. Individuals are much too small to be seen without a microscope.

Monera is a unicellular organism, they have a prokaryotic cellular organization, which means they lack well-defined, membrane-bounded organelles and nucleus. On the other hand, Protista is also unicellular organisms, but consist of eukaryotic cellular organization and well defined, membrane-bounded organelles and nucleus.

All forms of life on earth are divided into five categories on the support of the nutrition and energy they obtain, kind of cell (single cell or multi-celled), structural complexity, etc. These five kingdoms are Monera, Protists, Fungi, Plantae, and Animalia. Monera is the most primitive types of organisms which include blue-green algae (cyanobacteria), eubacteria and archaebacteria. While Protista represents the early evolution of eukaryotic cells.

Living things are classified in groups that have certain characteristics in common. The largest groups are called kingdoms. All living things can be classified as belonging to one of the five kingdoms: animals, plants, fungi, protists and monerans. Kingdoms can be divided into phyla (singular: phylum) or divisions and subphyla, which in turn can be separated into classes. Classes are divided into orders and suborders. These are separated into families and then into genera (singular: genus). Finally, each genus contains a number of species.

All living organisms are classified into groups based on very basic, shared characteristics. Organisms within each group are then further divided into smaller groups. These smaller groups are based on more detailed similarities within each larger group. This grouping system makes it easier for scientists to study certain groups of organisms. Characteristics such as appearance, reproduction, mobility, and functionality are just a few ways in which living organisms are grouped together. These specialized groups are collectively called the classification of living things. The classification of living things includes 7.

levels: Kingdom, phylum, classes, order, families, genus, and species.

Kingdoms

The most basic classification of living things is kingdoms. Currently there are Five kingdoms. Living things are placed into certain kingdoms based on how they obtain their food, the types of cells that make up their body, and the number of cells they contain.

Phylum

The phylum is the next level following kingdom in the classification of living things. It is an attempt to find some kind of physical similarities among organisms within a kingdom. These physical similarities suggest that there is a common ancestry among those organisms in a particular phylum.

Classes

Classes are way to further divide organisms of a phylum. As you could probably guess, organisms of a class have even more in common than those in an entire phylum. Humans belong to the Mammal Class because we drink milk as a baby.

Order

Organisms in each class are further broken down into orders. A taxonomy key is used to determine to which order an organism belongs. A taxonomy key is nothing more than a checklist of characteristics that determines how organisms are grouped together.

Families

Orders are divided into families. Organisms within a family have more in common than with organisms in any classification level above it. Because they share so much in common, organisms of a family are said to be related to each other. Humans are in the Hominidae Family.

Genus

Genus is a way to describe the generic name for an organism. The genus classification is very specific so there are fewer organisms within each one. For this reason there are a lot of different genera among both animals and plants. When using taxonomy to name an organism, the genus is used to determine the first part of its two-part name.

Species

Species are as specific as you can get. It is the lowest and most strict level of classification of living things. The main criterion for an organism to be placed in a particular species is the ability to breed with other organisms of that same species. The species of an organism determines the second part of its two-part name.

Scientists believe that humans and apes had a common ancestor. About five million years ago in Africa, some hominids (early humans) began to walk on two legs. Over millions of years, they developed bigger brains and began to spread out to other parts of the world. Later hominids began to make tools, develop language, use fire and wear clothes. The scientific name for modem people is sapiens Homo sapiens. They invented farming about 9000 years ago. Their early settlements led to the first civilizations.

Human evolution is the lengthy process of change by which people originated from apelike ancestors. Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years.

One of the earliest defining human traits, bipedalism -- the ability to walk on two legs -- evolved over 4 million years ago. Other important human characteristics -- such as a large and complex brain, the ability to make and use tools, and the capacity for language -- developed more recently. Many advanced traits -- including complex symbolic expression, art, and elaborate cultural diversity -- emerged mainly during the past 100,000 years.

Humans are primates. Physical and genetic similarities show that the modern human species, Homo sapiens, has a very close relationship to another group of primate species, the apes. Humans and the great apes (large apes) of Africa -- chimpanzees (including bonobos, or so-called “pygmy chimpanzees”) and gorillas -- share a common ancestor that lived between 8 and 6 million years ago. Humans first evolved in Africa, and much of human evolution occurred on that continent. The fossils of early humans who lived between 6 and 2 million years ago come entirely from Africa.

Most scientists currently recognize some 15 to 20 different species of early humans. Scientists do not all agree, however, about how these species are related or which ones simply died out. Many early human species -- certainly the majority of them – left no living descendants. Scientists also debate over how to identify and classify particular species of early humans, and about what factors influenced the evolution and extinction of each species.

Early humans first migrated out of Africa into Asia probably between 2 million and 1.8 million years ago. They entered Europe somewhat later, between 1.5 million and 1 million years. Species of modern humans populated many parts of the world much later. For instance, people first came to Australia probably within the past 60,000 years and to the Americas within the past 30,000 years or so. The beginnings of agriculture and the rise of the first civilizations occurred within the past 12,000 years.

One theory is that climate changes gradually led to a drop in dinosaur numbers. Another is that a huge meteorite hit the Earth, throwing up a massive dust cloud. Mammals managed to survive the climate change, but dinosaurs did not.

It was at this time when something happened that caused dinosaurs to become extinct. While there are several ideas, one that many scientists believe is that a huge comet or asteroid 6 to 12 miles wide slammed into the region that is now part of the eastern coast of Mexico, but at that time was under water.

The impact of this object is believed to have caused darkness over the entire earth for many months, due to the huge amounts of dust that were thrown into the atmosphere. A global wildfire would have destroyed over half of all living things. Water would have been poisoned in most places, and the earth would have sunk into a deep freeze while the dust was in the air.

Even through all this, some plants and animals survived, including some insects, fishes, frogs, crocodiles, turtles, birds, and mammoths.

This may have just been part of a series of changes that caused the extinction of the dinosaurs. Before the asteroid/comet hit the earth, massive eruptions of volcanoes had caused earth's climate to be changed. At about the same time, sea levels dropped dramatically, opening new land bridges, changing ocean currents, and affecting the climate. These changes in climate likely reduced the ability of the dinosaurs to adapt, and the impact from the asteroid/comet was the last straw. The creatures that were able to survive all these changes came to dominate the landscape. Mammals grew larger, and moved into new areas, taking over locations that had previously been the habitat of dinosaurs.

Changes in sea levels, ocean currents, and other events were also bringing in a new climatic cycle to the earth. Huge ice sheets would begin to cover large areas of the earth on a periodic basis. These swings in climate would have a major effect on animal habitats.

Over time, the remains of plants and animals decay. Fossilization is one way in which their forms have survived to give us information about prehistoric times. Since the time of the dinosaurs, however, the climate of parts of the Earth has cooled. In recent years, frozen remains of mammoths and even humans have been found, preserved in the ice of polar or mountainous regions.

Paleoanthropology to hear the preceding term pronounced is the study of early forms of humans and their primate ancestors.  It is similar to paleontology to hear the preceding term pronounced except its focus is documenting and understanding human biological and cultural evolution.  Paleoanthropologists do not look for dinosaurs and other early creatures.  However, like paleontology, the data for paleoanthropology is found mainly in the fossil record.  Before examining this evidence, it is necessary to first learn what fossils are and how they are formed.  In addition, it is important to know how paleoanthropologists date fossils and other evidence of the prehistoric past.

Taphonomy to hear the preceding term pronounced is the study of the conditions under which plants, animals, and other organisms become altered after death and sometimes preserved as fossils.  Research into these matters has shown that fossilization is a rare phenomenon.  In order for a fossil to form, the body must not be eaten or destroyed by erosion and other natural forces.  Preservation would most likely occur if the organism were buried quickly and deeply.  In most environments, soft body parts, such as skin, muscle, fat, and internal organs, deteriorate rapidly and leave no trace.  Only very rarely do we find the casts of such tissues.  Similarly, the totally soft-bodied creatures, like jellyfish, are very uncommon fossils.  Hard body parts, such as dense bones, teeth, and shells, are what most often are preserved.  It is likely that the vast majority of fossils will never be found before they are destroyed by erosion.  That coupled with the fact that extremely few living things are preserved long enough after death to become fossils makes the large collections of fossils in the museums of the world quite remarkable.  It is a testament to the tenacious searching by fossil hunters over the last two centuries.

People often think of fossils as being mineralized bones or shells stored in museums.  However, they can be any remains or traces of ancient organisms.  They even can be footprints, burrows, or casts of bodies with nothing else surviving.  Some of the best preserved fossils were rapidly frozen in permafrost soil or ice, dehydrated in dry desert caves, or encased in tree resin that hardened into amber.  In any of these three environmental conditions, even soft body parts can be remarkably well preserved indefinitely. 

Several wooly mammoths that lived during the last ice age have been excavated from frozen tundra soil in Siberia.  Some were still in such good condition, that parts of their bodies were fed to the dogs of the Russian scientists who found them.  One small mammoth was even transported intact to Moscow where it is kept in a specially made large freezer that allows it to be displayed for the general public.  The oldest frozen human remains were discovered on the edge of a glacier in the Alps of northern Italy in 1991.  It was a well preserved body of a man, along with his clothes and tools, who died about 5,300 years ago.  Even tattoos on his skin were preserved by the extreme cold. 

Dinosaur fossils, even when they show the skin of the animal, cannot show us what colour it was. Dinosaurs may have been green and brown in colour, camouflaging them amongst the leaves and rocks. It is also possible that some of them were very brightly coloured, just as some tropical lizards are today.

While skin impressions have been found — suggesting a pebbly or scaly texture — no real dinosaur skin remains. That means paleontologists don't know for certain what color any of the dinosaurs were. They do have several theories, though. For example, many believe that dinosaur skin was probably drab shades of gray or green, allowing them to blend into their surrounding environments. This dull coloration would help them escape the detection of predators, enabling some to survive longer. Because large modern-day warm-blooded animals, such as elephants and rhinoceroses, tend to be dully colored, many scientists think that dinosaurs were, too.

But other paleontologists say the opposite is true — that dinosaurs' skin could have been shades of purple, orange, red, even yellow with pink and blue spots! Rich and varied colors, they argue, might have helped dinosaurs to recognize one another and attract mates. Because research has shown that dinosaurs'closest living relatives — birds — can see in color, it is theorized that dinosaurs could, too. Scientists in this camp believe that color may well have been as important to these ancient creatures as it is to us.

Jack Horner, Curator of Paleontology at the Museum of the Rockies, Denver, Colorado, explains, "Some male dinosaurs may have had brightly colored crests to help them attract mates, but females probably did not. This color differentiation is also found in many modern-day birds."

During the 150 million years that they lived on Earth, dinosaurs certainly included the largest creatures to live on land and the fiercest hunters. But they were not the only animals to live successfully on Earth by any means. There were many species of insect and the earliest winged animals could be seen in the skies. The seas were teeming with fish and other sea-life. The first mammals were also thriving, ready to become the dominant creatures when the dinosaurs became extinct.

It is often said that dinosaurs ruled the earth. Movies such as Jurassic Park, the media, and educational books constantly promote the evolutionary claim that dinosaurs dominated planet earth for well over 100 million years. In the evolutionary paradigm, mankind had not yet evolved, and before the 65-million-year-old extinction mark, mammals were small rodents who steered clear of the ruling dinosaurs.

The prevailing evolutionary model argues that the coexistence of dinosaurs, large mammals, and humans is not supported for four reasons. First, dinosaur and human fossils have never been discovered together in the fossil record. Second, large mammals have never been discovered in ‘dinosaur’ rock. Third, dinosaurs could not have existed with larger mammals due to intense competition in similar environments. Fourth, dinosaurs would have overrun human civilization due to their monolithic size and belligerence. However, these arguments do not stand up to closer scrutiny and the weight of the evidence provides far greater support to biblical creation.

The historical narrative of Genesis plainly records that God created all land animals and human beings on the sixth day of creation about 6,000 years ago. According to the Bible, dinosaurs, mammals, and humans have coexisted from the beginning of creation. This is in direct contradiction to the evolutionary model of earth history. And although the idea of dinosaurs and human beings living at the same time is ridiculed as illogical and unscientific, a more open-minded approach reveals a different story. Circumstantial evidence in the fossil record, literary and artistic accounts in human civilization, and observational examples in present-day ecological habitats lend a high degree of credibility to the biblical account.

Living things inherit characteristics from the generations that have gone before, but each individual is slightly different. Over many generations, the differences that are more successful survive, so that the species gradually adapts. In time, these changes, called evolution, can lead to major adaptations and even new species. All living things have evolved from the simple organisms that began to grow in the Earth’s waters. Many of these, such as the dinosaurs, have since become extinct, although they may have lived successfully on Earth for millions of years.

The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of Species" in 1859, is the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring. 

Evolution by natural selection is one of the best substantiated theories in the history of science, supported by evidence from a wide variety of scientific disciplines, including paleontology, geology, genetics and developmental biology.

The theory has two main points, said Brian Richmond, curator of human origins at the American Museum of Natural History in New York City. "All life on Earth is connected and related to each other," and this diversity of life is a product of "modifications of populations by natural selection, where some traits were favored in and environment over others," he said.

More simply put, the theory can be described as "descent with modification," said Briana Pobiner, an anthropologist and educator at the Smithsonian Institution National Museum of Natural History in Washington, D.C., who specializes in the study of human origins.

The theory is sometimes described as "survival of the fittest," but that can be misleading, Pobiner said. Here, "fitness" refers not to an organism's strength or athletic ability, but rather the ability to survive and reproduce.

For example, a study on human evolution on 1,900 students, published online in the journal Personality and Individual Differences in October 2017 found that many people may have trouble finding a mate because of rapidly changing social technological advances that are evolving faster than humans. "Nearly 1 in 2 individuals faces considerable difficulties in the domain of mating," said lead study author Menelaos Apostolou, an associate professor of social sciences at the University of Nicosia in Cyprus. "In most cases, these difficulties are not due to something wrong or broken, but due to people living in an environment which is very different from the environment they evolved to function in." 

Ever since human beings first lived on Earth they have been finding fossilized remains. But it was really only in the nineteenth century that scientific study of the fossils took place. Until then, people believed that the fossils came from dragons, giants or even unicorns!

Thanks to modern science, we know a lot about the dinosaurs that used to roam Earth. How do scientists know so much? It's not like they can observe them in the wild like they do with modern animals. Instead, they rely upon what dinosaurs left behind. No, not their diaries! Scientists study their fossilized bones and, sometimes, other bodily material.

No one knows when the first dinosaur bone was found. Ancient peoples most likely uncovered fossils of dinosaur bones from time to time, but they had no idea what they had found. Ancient Chinese writings from over 2,000 years ago reference "dragon" bones, which many experts today believe had to be dinosaur fossils.

Even early scientists weren't sure about the fossils they found. For example, in 1676, Reverend Robert Plot, a curator of an English museum, discovered a large thigh bone in England. He believed it belonged to ancient species of human "giants." Although the specimen disappeared eventually, drawings of it remain. Based upon those drawings, modern scientists believe it was probably from a dinosaur known as "Megalosaurus."

Megalosaurus is believed to be the first dinosaur ever described scientifically. British fossil hunter William Buckland found some fossils in 1819, and he eventually described them and named them in 1824. Like scientists before him, Buckland thought the fossils belonged to an ancient, larger version of a modern reptile.

As of that time, the word "dinosaur" still had not been invented yet, and dinosaurs hadn't yet been recognized as distinct creatures that were significantly different than modern reptiles. All that changed when British scientist Richard Owen came along.

In late 1841 or early 1842, Owen viewed the fossil collection of William Devonshire Saul. He was intrigued by a fossilized chunk of spine, which was thought to belong to an ancient reptile similar to an iguana that had been called "Iguanodon."

Owen began comparing the fossils he saw and, within a few months, came to two critical conclusions: (1) that the fossils were from similar creatures; and (2) these were creatures unlike anything on Earth today. He coined the term "dinosaurs," which means "terrible lizards."

The periods when the Earth was forming and early kinds of life were developing have been given names. There is also a short way of saying “55 million years ago”: 55mya.

Prehistory is the time before people began to write. The word comes from the Ancient Greek words (pre = "before") and history. Paul Tournal first used the French word Prehistorique. He found things made by humans more than ten thousand years ago in some caves in France. The word was first used in France around 1830 to talk about the time before writing. Daniel Wilson used it in English in 1851.

The term is mostly used for the period from 12,000 BC – 3000 BC, roughly speaking, the Neolithic. Sometimes the term "prehistoric" is used for much older periods, but scientists have more accurate terms for those more ancient times.

Less is known about prehistoric people because there are no written records (history) for us to study. Finding out about pre-history is done by archeology. This means studying things like tools, bones, buildings and cave drawings. Pre-history ends at different times in different places when people began to write.

In the more ancient Stone Age pre-history, people lived in tribes and lived in caves or tents made from animal skin. They had simple tools made from wood and bones, and cutting tools from stone such as flint, which they used to hunt and to make simple things. They made fire and used it for cooking and to stay warm. They made clothing out of animal skins, and later by weaving. Society started when people began doing specialized jobs. This is called the division of labour. The divisions of labor made people depend on one another and led to more complex civilizations.

Some important sciences that are used to find out more about pre-history are palaeontology, astronomy, biology, geology, anthropology, and archaeology. Archaeologists study things left over from prehistory to try to understand what was happening. Anthropologists study the traces of human behavior to learn what people were doing and why.

After people started to record events, first by drawing symbols (called pictographs) and then by writing, it became much easier to tell what happened, and history started. These records can tell us the names of leaders (such as Kings and Queens), important events like floods and wars, and the things people did in their daily lives. The time when prehistory ended and history started is different in different places, depending on when people began to write and if their records were kept safe or lost so they could be found later on. In places like Mesopotamia, China, and Ancient Egypt, things were recorded from very early times (around 3200 BC in Ancient Egypt) and these records can be looked at and studied. In New Guinea, the end of prehistory came much later, around 1900.

          Almost everything that we know about the living things on Earth before humans evolved has been learnt from fossils. Fossils are the remains of dead animals and plants that have been turned to stone over millions of years.

          Because, by definition, there are no written records from prehistoric times, much of the information we know about the time period is informed by the fields of paleontology and archeology—the study of ancient life through fossils and the study of the material left behind by ancient peoples, including the cave painting of Lascaux, and such constructions as Stonehenge in southern England and the huge earthworks at Silbury Hill. There is much that is still unknown about the purpose of these “artifacts,” but the caves show an early ability to create art while Stonehenge demonstrates knowledge of astronomy. It is also possible that religious beliefs and practices were associated with these prehistoric monuments, perhaps involving the winter and spring Equinoxes.

          Human prehistory differs from history not only in terms of chronology but in the way it deals with the activities of archaeological cultures rather than named nations or individuals. Restricted to material remains rather than written records (and indeed only those remains that have survived), prehistory is anonymous. Because of this, the cultural terms used by prehistorians, such as Neanderthal or Iron Age are modern, arbitrary labels, the precise definition of which are often subject to discussion and argument. Prehistory thus ends when we are able to name individual actors in history, such as Snofru, founder of the Fourth Dynasty of Egypt, whose reign began circa 2620 B.C.E.

          The date marking the end of prehistory, that is the date when written historical records become a useful academic resource, varies from region to region. In Egypt it is generally accepted that prehistory ended around 3500 B.C.E. whereas in New Guinea the end of the prehistoric era is set much more recently, at around 1900 C.E. The earliest historical document is said to be the Egyptian Narmer Palette, dated 3200 B.C.E.

Picture Credit : Google

          The surface of the Earth is changing all the time. When living things first began to evolve on Earth, there was just one huge continent. Over millions of years, this continent broke up and moved to become the land masses we recognize today. This is why similar dinosaur fossils have been found in very different parts of the world, although dinosaurs were land creatures and could not cross the oceans.

          The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geological change and biological evolution.

          The geological time scale (GTS), as defined by international convention, depicts the large spans of time from the beginning of the Earth to the present, and its divisions chronicle some definitive events of Earth history. (In the graphic: Ga means "billion years ago"; Ma, "million years ago".) Earth formed around 4.54 billion years ago, approximately one-third the age of the universe, by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere and then the ocean, but the early atmosphere contained almost no oxygen. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. While the Earth was in its earliest stage (Early Earth), a giant impact collision with a planet-sized body named Theia is thought to have formed the Moon. Over time, the Earth cooled, causing the formation of a solid crust, and allowing liquid water on the surface.

          The Hadean eon represents the time before a reliable (fossil) record of life; it began with the formation of the planet and ended 4.0 billion years ago. The following Archean and Proterozoic eons produced the beginning of life on Earth and its earliest evolution. The succeeding eon is the Phanerozoic, divided into three eras: the Palaeozoic, an era of arthropods, fishes, and the first life on land; the Mesozoic, which spanned the rise, reign, and climactic extinction of the non-avian dinosaurs; and the Cenozoic, which saw the rise of mammals. Recognizable humans emerged at most 2 million years ago, a vanishingly small period on the geological scale.

          The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era, after a geological crust started to solidify following the earlier molten Haden Eon. There are microbial mat fossils such as stromatolites found in 3.48 billion-year-old sandstone discovered in Western Australia. Other early physical evidence of a biogenic substance is graphite in 3.7 billion-year-old metasedimentary rocks discovered in southwestern Greenland as well as "remains of biotic life" found in 4.1 billion-year-old rocks in Western Australia. According to one of the researchers, "If life arose relatively quickly on Earth … then it could be common in the universe."

          Photosynthetic organisms appeared between 3.2 and 2.4 billion years ago and began enriching the atmosphere with oxygen. Life remained mostly small and microscopic until about 580 million years ago, when complex multicellular life arose, developed over time, and culminated in the Cambrian Explosion about 541 million years ago. This sudden diversification of life forms produced most of the major phyla known today, and divided the Proterozoic Eon from the Cambrian Period of the Paleozoic Era. It is estimated that 99 percent of all species that ever lived on Earth, over five billion, have gone extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million are documented, but over 86 percent have not been described. However, it was recently claimed that 1 trillion species currently live on Earth, with only one-thousandth of one percent described.

          The Earth's crust has constantly changed since its formation, as has life since its first appearance. Species continue to evolve, taking on new forms, splitting into daughter species, or going extinct in the face of ever-changing physical environments. The process of plate tectonics continues to shape the Earth's continents and oceans and the life they harbor. Human activity is now a dominant force affecting global change, harming the biosphere, the Earth's surface, hydrosphere, and atmosphere with the loss of wild lands, over-exploitation of the oceans, production of greenhouse gases, degradation of the ozone layer, and general degradation of soil, air, and water quality.

Picture Credit : Google