Planet earth in a nutshell

PLANET EARTH IN A NUTSHELL 1

EARTH: THE ONLY ABODE OF LIFE 2

A UNIQUE PLANET Situated at the right distance from the Sun. Has oceans of liquid water on surface. Green vegetation provides life-supporting oxygen. Wind and ocean currents maintain heat balance and help moderate the temperature. Has a relatively large satellite that has tidal effect. 3

FROM A MOLTEN PAST Earth was formed some 4,500 million years ago. Had no oceans, no oxygen in the atmosphere, and no living beings. Heavy bombardment of rocks and internal radioactive decay caused early Earth to melt. Heavier elements sank to the centre while lighter ones rose to the surface, producing Earth’s various layers. 4

PEEPING INTO EARTH’S INTERIOR Seismic waves slow down when they pass through hot molten rocks and speed up while passing through cold solid rocks, which make it possible to study Earth’s inner structure. 5

LAYERS OF EARTH From seismic studies it is known that the Earth is composed of several layers, somewhat like the layers of an onion. 6

LAYERS OF EARTH The outermost layer is the crust, composed mainly of compounds of aluminium and silicates. The next layer is the mantle, composed mainly of rocks containing iron and magnesium silicates. The innermost layer is the core, made up of mostly iron and nickel. 7

LAYERS OF EARTH 8

THE ‘SPHERES’ OF EARTH The crust and the upper portion of the mantle are together known as the ‘lithosphere.’ Much of Earth is covered by a layer of water or ice called the ‘hydrosphere’. The thin layer of air that surrounds the Earth is the ‘atmosphere’. The portion of the hydrosphere, atmosphere, and solid land where life exists is together known as the ‘biosphere’. 9

EARTH’S MANTLE Unlike the crust, which is mostly hard rock, the mantle is a highly viscous plastic-like material that can flow. The molten mass in the mantle is in constant motion, which makes the continental plates move. The mantle is also the place where most gemstones such as diamonds and garnets are formed. 10

EARTH’S CORE The core is divided into two layers, the outer core and the inner core. Mainly made up of iron and nickel. Temperatures range from 4,000 to 7,500C. The outer core and the inner core together produce Earth’s magnetism. Earth’s magnetism is what makes the magnetic compass work. 11

EARTH’S MOVING CONTINENTS The German meteorologist Alfred Wegener had first proposed in 1912 that the world’s continents were once joined together in a giant supercontinent which he called ‘Pangaea.’ 12

MOVING CONTINENTS Sometime around 200 million years ago, Pangaea broke up and the fragments began to move away from one another, forming the present-day continents we see today. 13

FOOTPRINT OF CONTINENTS 14

EARTH’S GRINDING PLATES Earth’s lithosphere, composed of a set of large and small continental plates that are constantly moving. When the plates move they either collide, or go under the other, or slide past each other. Plate boundaries are subject to extreme pressures and are the sites where violent processes like earthquakes and volcanic eruptions occur. 15

FRACTURED EARTH The moving plates give the Earths crust the appearance of a giant fractured globe. 16

BUILDING MOUNTAINS Where two plates collide the resulting pressure is often so great that it deforms the surface into folds leading to formation of high mountain ranges. 17

RISE OF THE HIMALAYAS Such collision created a series of long, parallel folds in the Earth’s crust  the Himalayan range that contains all the worlds mountains over 7,000 metres in height. 18

SPREADING SEA FLOORThe mid-oceanic ridge is the region where Earth’scrustal plates are moving apart, creating new oceanfloor. 19

SEA FLOOR GOING UNDERDestruction of ocean floor occurs at plate boundaries,along areas called ‘subduction zones’ where oceaniccrust goes under either continental crust or oceaniccrust. 20

RING OF FIRE Subduction zones are regions of high volcanic activity and have led to the formation of the spectacular mountain chain aroundthe Pacific Ocean known as the ‘Ring of Fire.’ 21

DYNAMIC EARTH So, we now know that our Earth is a dynamic planet. Directly or indirectly, plate tectonics influences nearly all geologic processes. The knowledge of plate tectonics has given us the power to understand violent geological phenomena like earthquakes and volcanic eruptions and to safeguard against loss of life and property. 22

EARTH’S PROTECTIVE ATMOSPHERE The Earths atmosphere is a very thin layer of air wrapped around a very large planet. Two gases make up the bulk of the Earths atmosphere: nitrogen (78%) and oxygen (21%). Various trace gases make up the remainder. Based on temperature, the atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere. Energy is transferred between the Earths surface and the atmosphere via conduction, convection, and radiation. 23

A BLANKET OF AIR One of the most vital components of Earth’s immediate environment is its atmosphere 24

LAYERS OF EARTH’S ATMOSPHERE The temperature of the atmosphere varies with height, but not in a regular manner. The highest temperature is found in the thermosphere, which begins at an altitude of 80 km. 25

THE OZONE SHIELD A layer of ozone in the stratosphere is crucial to our survival; this layer filters out harmful ultraviolet rays from the Sun. But it is being destroyed. 26

WATER ON EARTHThe water of Earths hydrosphere is not static;it gets constantly recycled. Evaporation by the Sun, condensation into cloud; precipitation as rain and flow into rivers and ocean maintain the cycle. 27

ROCKS OF MANY FORMS Rocks of Earths lithosphere are mainly of three types – sedimentary, metamorphic, and igneous. The three types are constantly cycled through a geological process known as the ‘rock cycle.’ The process depends on temperature, pressure, time and conditions within the Earth. 28

EARTH’S ROCK CYCLE 29

SEDIMENTARY ROCK 30

METAMORPHIC ROCK 31

IGNEOUS ROCK 32

DAWN OF LIFE It is believed that all living organisms evolved from single-cell organisms that appeared when the first solid crust formed, almost 4,000 million years ago. By 3,500 million years ago, the Earth’s oceans were populated by one-celled organisms called prokaryotes. In course of time, higher forms of life evolved and today living forms occupy almost every nook and corner of the globe. 33

EARLIEST FOSSILSStromatolites area majorconstituent of thefossil record forabout the first3.5 billion yearsof life on Earth,with theirabundancepeaking about1,250 millionyears ago. 34

THE OXYGEN GIVERSThe atmosphere of early Earth did not have oxygen,which appeared only after organisms calledcyanobacteria, commonly known as ‘blue-greenalgae’ appeared about 3,000 million years ago. 35

GREENING OF THE EARTH The earliest evidence of land plants and fungi appears in the fossil record around 435 million years ago. Plants play the most important part in the cycle of nature. They are the only organisms that can make their own food. All other animals including humans depend on them for food. 36

DIVERSE FORMS The first flowering plants – also called angiosperms – appeared around 145 million years ago Today, more than 250,000 species comprise the Plant Kingdom. Some plants are so small they can barely be seen. Others are taller than skyscrapers. Plants play an important role in the shaping of the environment. 37

ABUNDANCE OF LIFE As the oxygen level in atmosphere increased, organisms, known as eukaryotes, appeared. Gradually, by 500 million years ago, there was an explosion of multi-cellular organisms. By 435 million years ago the early vertebrates had appeared in the ocean. By about 430 million years ago, primitive life forms including plants and insects appeared on land followed by spiders and amphibians. 38

THE AGE OF DINOSAURS Dinosaurs emerged by about 240 million years. They were reptiles and most of them hatched from eggs.But the dinosaurs were wiped out by acataclysmic event about 65 million years ago. 39

RISE OF MAMMALS The demise of the dinosaurs saw mammals growing bigger and more diverse. Within 10,000,000 years after the death of the dinosaurs, the world was filled with rodent-like mammals, and large herbivorous and carnivorous mammals. Around 1.8 million years ago, the earliest direct ancestors of modern humans appeared in Africa. 40

THE HUMAN INVASION The first modern humans, Homo sapiens, appeared on Earth about 195,000 years ago in Africa. After spreading through Europe and Southeast Asia, populations of modern humans moved into North America in the north and Australia in the south. Agriculture began about 12,000 years ago. 41

EXPLODING POPULATIONS With the availability of assured food supply the world population started rising sharply. From just one million in 10,000 BC it shot up to 27 million by 2000 BC. By AD 1000 it was 254 million. By AD 2000 the world population had crossed the 6,000 million mark and is expected to nearly double by 2050 42

EXPLODING POPULATION 43

THREAT TO EARTH’S BIOSPHERE Humans constitute only one of 4,500 species of mammals that exist on Earth. The human species is only one species in the estimated 30 to 100 million species that form the Earths complex biosphere. Yet, the damage that humans have wrought to the biosphere is irreparable and may even spell doom for many species. 44

DISAPPEARING FORESTSDespite their vital role as a carbon dioxide sink, thetropical rainforests are being destroyed at a rate of500,000 square km per year and will disappear soon. 45

VANISHING WILDLIFEDeforestation is also destroying the natural habitatof several species, threatening their extinction. 46

POLLUTED WATER BODIESIndiscriminate discharge of industrial and domesticwaste in rivers and water bodies is seriouslydegrading Earth’s water resources. 47

EARTH AS A HOT HOUSE Increasing accumulation of carbon dioxide in Earth’s atmosphere due to burning of fossil fuels has upset the carbon dioxide balance in the atmosphere, leading to enhanced greenhouse effect. This is causing the Earth to get warmer, with serious consequences. 48

MELTING ICE CAPSAs the Earth heats up, Polar ice caps are melting,threatening survival of several species. Warming ofthe Poles also has serious impact on global weather. 49

RECEDING GLACIERS As the Earth becomes hotter, glaciers are receding. The Gangotri glacier, source of the river Ganges, has been receding at such an alarming rate that environmentalists fear that if urgent measures are not undertaken, a time may come when the Ganges may just disappear. 50

SAVING PLANET EARTH Earth’s resources are limited; they need to be conserved. Earth’s environment is fragile; it needs protection from pollution and degradation. Carbon emission can be reduced by more efficient use of energy and adoption of non- conventional energy sources. For all living beings, including humans, the Earth remains the only abode. It needs to be saved! 51

Thank you!Sandipan DharEmail id: sandipandhar@gmail.com 52

Planet earth in a nutshell

by Sandipan Dhar

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