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Category Life on Earth

WHAT IS EVOLUTION?

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.” 

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WHEN WERE FOSSILS DISCOVERED?

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.”

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HOW ARE PREHISTORIC TIMES DESCRIBED?

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.

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HOW DO WE KNOW ABOUT PREHISTORY?

          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.

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WHEN DID THE EARTH BEGIN TO LOOK AS IT DOES TODAY?

          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.

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WHAT WERE THE FIRST LIVING THINGS ON EARTH?

          Although viruses are the simplest living things, they need to live and reproduce themselves inside a larger organism, so they are unlikely to have been the first living things on Earth. The earliest evidence of life that has been found is tiny fossils of primitive bacteria in rocks about 3800 million years old. Later, blue-green algae evolved. They could use energy from the Sun and in so doing gave off oxygen. Modern plants and animals share these simple organisms as ancestors.

          The earliest evidence for life on Earth arises among the oldest rocks still preserved on the planet. Earth is about 4.5 billion years old, but the oldest rocks still in existence date back to just 4 billion years ago. Not long after that rock record begins, tantalizing evidence of life emerges: A set of filament-like fossils from Australia, reported in the journal Astrobiology in 2013, may be the remains of a microbial mat that might have been extracting energy from sunlight some 3.5 billion years ago. Another contender for world’s oldest life is a set of rocks in Greenland that may hold the fossils of 3.7-billion-yer-old colonies of cyanobacteria, which form layered structures called stromatolites.

          Some scientists have claimed to see evidence of life in 3.8-billion-year-old rocks from Akilia Island, Greenland. The researchers first reported in 1996 in the journal Nature that isotopes (forms of an element with different numbers of neutrons) in those rocks might indicate ancient metabolic activity by some mystery microbe. Those findings have been hotly debated ever since — as, in fact, have all claims of early life.

          Most recently, scientists reported in the journal Nature that they had discovered microfossils in Canada that might be between 3.77 billion and 4.29 billion years old, a claim that would push the origins of life to very shortly after Earth first formed oceans. The filament-like fossils contained chemical signals that could herald life, but it’s hard to prove that they do, researchers not involved in the study told Live Science. It’s also hard to prove that fossils found in ancient rocks are necessarily ancient themselves; fluids have penetrated cracks in the rock and might have allowed newer microbes in to older rock. The researchers used samarium-neodymium dating to arrive at the 4.29 billion maximum age for the fossils. This method, which uses the decay of one rare-earth element into another, may measure the age of the magma that formed the rocks rather than the rocks themselves, an issue that has also dogged claims of the Earth’s oldest rocks.   

          Still, the fact that suggestive evidence of life arises right as the rock record begins raises a question, said University of California, Los Angeles, geochemist Elizabeth Bell in a SETI Talk in February 2016: Is the timing a coincidence, or were there earlier forms of life whose remnants disappeared with the planet’s most ancient rocks?

          The period that occurred before the rock record begins is known as the Hadean. It was an extreme time, when asteroids and meteorites pummeled the planet. Bell and her colleagues said they might have evidence that life arose during this very unpleasant time. In 2015, the research team reported discovering graphite, a form of carbon, in 4.1-billion-year-old crystals of zircon. The ratio of isotopes in the graphite suggested a biological origin, Bell and her colleagues wrote in the journal Proceedings of the National Academy of Sciences.

          “There is some skepticism, which is warranted,” Bell told Live Science. Meteorites or chemical processes might have caused the odd carbon ratios, she said, so the isotopes alone aren’t proof of life. Since the publication of the 2015 paper, Bell said, the researchers have found several more of the rare-carbon inclusions, which the scientists hope to analyze soon.

          From what is known of this period, there would have been liquid water on the planet, Bell told Live Science in an interview. There might have been granite, continental-like crust, though that’s controversial, she said. Any life that could have existed would have been a prokaryote (a single-celled organism without membrane-bound nuclei or cell organelles), Bell added. If there was continental crust on Earth at the time, she said, prokaryotes might have had mineral sources of nutrients like phosphorus.

          A different approach to the hunt for Earth’s early life suggests that oceanic hydrothermal vents may have hosted the first living things. In a paper published in July 2016 in the journal Nature Microbiology, researchers analyzed prokaryotes to find the proteins and genes common to all of these organisms, presumably the final remnants of the Last Universal Common Ancestor (LUCA) — the first shared relative from which all life today descends.

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WHEN DID LIFE BEGIN ON EARTH?

          The Earth began to be formed over 4.5 billion years ago, but for millions of years nothing could live here. Gradually, the Earth’s crust and the atmosphere formed. The simplest forms of life, bacteria and algae, probably began to grow less than four billion years ago. Human beings did not appear until about two million years ago.

          Microbial life forms have been discovered on Earth that can survive and even thrive at extremes of high and low temperature and pressure, and in conditions of acidity, salinity, alkalinity, and concentrations of heavy metals that would have been regarded as lethal just a few years ago. These discoveries include the wide diversity of life near sea–floor hydrother­mal vent systems, where some organisms live essentially on chemical energy in the absence of sunlight. Similar environments may be present elsewhere in the solar system.

          Under­standing the processes that lead to life, however, is complicated by the actions of biology itself. Earth’s atmosphere today bears little resemblance to the atmosphere of the early Earth, in which life developed; it has been nearly reconstituted by the bacteria, vegetation, and other life forms that have acted upon it over the eons. Fortunately, the solar system has preserved for us an array of natural laboratories in which we can study life’s raw ingredients — volatiles and organics — as well as their delivery mechanisms and the prebiotic chemical processes that lead to life. We can also find on Earth direct evidence of the interactions of life with its environments, and the dramatic changes that life has undergone as the planet evolved. This can tell us much about the adaptability of life and the prospects that it might survive upheavals on other planets.

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WHAT CAN VOLCANOES TELL US?

          One interesting aspect of volcanic eruptions is that surrounding areas are covered rapidly in molten rock or ash, sometimes preserving the animals, plants and structures underneath. Archaeologists have been able to study life in Roman times, for example, by examining the remains of Pompeii, in Italy, buried when Vesuvius erupted in AD 79.

          I guess the main good effect that volcanoes have on the environment is to provide nutrients to the surrounding soil. Volcanic ash often contains minerals that are beneficial to plants, and if it is very fine ash it is able to break down quickly and get mixed into the soil.

          Perhaps the best place to look for more information about this would be to look up references about some of the countries where lots of people live in close proximity to volcanoes and make use of the rich soils on volcanic flanks. These would include Indonesia, The Philippines, Japan, Italy, etc.

          I suppose another benefit might be the fact that volcanic slopes are often rather inaccessible, especially if they are steep. Thus they can provide refuges for rare plants and animals from the ravages of humans and livestock.

          Finally, on a very fundamental scale, volcanic gases are the source of all the water (and most of the atmosphere) that we have today. The process of adding to the water and atmosphere is pretty slow, but if it hadn’t been going on for the past 4.5 billion years or so we’d be pretty miserable.

          Volcanoes have done wonderful things for the Earth. They helped cool off the earth removing heat from its interior. Volcanic emissions have produced the atmosphere and the water of the oceans. Volcanoes make islands and add to the continents.

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WHY DO VOLCANOES ERUPT?

          Like earthquakes, volcanoes mainly occur along fault lines. Molten rock, gases and ash are forced out through a gap in the Earth’s crust to release the pressure beneath. Over thousands of years, cooled rock sometimes builds up around the fissure in the ground to form the familiar conical shape of a volcano.

          Deep within the Earth it is so hot that some rocks slowly melt and become a thick flowing substance called magma. Since it is lighter than the solid rock around it, magma rises and collects in magma chambers. Eventually, some of the magma pushes through vents and fissures to the Earth’s surface. Magma that has erupted is called lava.

          Some volcanic eruptions are explosive and others are not. The explosivity of an eruption depends on the composition of the magma. If magma is thin and runny, gases can escape easily from it. When this type of magma erupts, it flows out of the volcano. A good example is the eruptions at Hawaii’s volcanoes. Lava flows rarely kill people because they move slowly enough for people to get out of their way. If magma is thick and sticky, gases cannot escape easily. Pressure builds up until the gases escape violently and explode. A good example is the eruption of Washington’s Mount St. Helens. In this type of eruption, the magma blasts into the air and breaks apart into pieces called tephra. Tephra can range in size from tiny particles of ash to house-size boulders.

          Explosive volcanic eruptions can be dangerous and deadly. They can blast out clouds of hot tephra from the side or top of a volcano. These fiery clouds race down mountainsides destroying almost everything in their path. Ash erupted into the sky falls back to Earth like powdery snow. If thick enough, blankets of ash can suffocate plants, animals, and humans. When hot volcanic materials mix with water from streams or melted snow and ice, mudflows form. Mudflows have buried entire communities located near erupting volcanoes.

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WHAT IS A GEYSER?

          In some areas, underground lakes, rivers and springs are heated by molten rocks below. The hot water bubbles to the surface in springs and forms pools, or it may shoot upwards under great pressure, forming a geyser.

          Geysers result from the heating of groundwater by shallow bodies of magma. They are generally associated with areas that have seen past volcanic activity. The spouting action is caused by the sudden release of pressure that has been confining near-boiling water in deep, narrow conduits beneath a geyser. As steam or gas bubbles begin to form in the conduit, hot water spills from the vent of the geyser, and the pressure is lowered on the water column below. Water at depth then exceeds its boiling point and flashes into steam, forcing more water from the conduit and lowering the pressure further. This chain reaction continues until the geyser exhausts its supply of boiling water.

          The boiling temperature of water increases with pressure; for example, at a depth of 30 metres (about 100 feet) below the surface, the boiling point is approximately 140 °C (285°F). Geothermal power from steam wells depends on the same volcanic heat sources and boiling temperature changes with depth that drive geyser displays.

          As water is ejected from geysers and is cooled, dissolved silica is precipitated in mounds on the surface. This material is known as sinter. Often geysers have been given fanciful names (such as Castle Geyser in Yellowstone National Park) inspired by the shapes of the colourful and contorted mounds of siliceous sinter at the vents.

         Geysers are rare. There are more than 300 of them in Yellowstone in the western United States —approximately half the world’s total—and about 200 on the Kamchatka Peninsula in the Russian Far East, about 40 in New Zealand, 16 in Iceland, and 50 scattered throughout the world in many other volcanic areas. Perhaps the most famous geyser is Old Faithful in Yellowstone. It spouts a column of boiling water and steam to a height of about 30 to 55 metres (100 to 180 feet) on a roughly 90-minute timetable.

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