Homo sapiens

http://www.philosophyforum.net/HistTimeline_files/HistTimeline.htm

For grade 6

The Science of the Water Cycle for Kids

What is the Water Cycle? 

The water cycle is a way that water moves all around the Earth. It never stops and doesn't really have a beginning or an end. It's like a big circle. We'll describe it by starting with water that's on land. For example, water in the ocean or a lake. Some water on the surface of the ocean will evaporate due to heat from the sun. When it evaporates it turns into vapor water and goes up into the atmosphere. This vapor water gets together with a lot of other vapor water and turns into clouds. Clouds move about the earth with the weather and once they are so full of water they drop the water to Earth in some form of precipitation. It could be rain, snow, sleet, or hail. When the water hits the earth it may fall right back into the ocean or feed a flower or be snow on the top of a mountain. Eventually this water will evaporate and start the whole cycle again. 

How water goes from land to vapor in the atmosphere 

There are three main ways that water on land turns into vapor: 

Evaporation - This is the main process by which water goes from the ground to vapor in the atmosphere. Around 90 percent of the water vapor in the atmosphere got there through evaporation. Evaporation takes place only on the water's surface. It takes energy in the form of heat. Hot water will evaporate more easily than cold water. The sun provides a lot of the energy for evaporation in the water cycle, primarily causing evaporation from the surface of the ocean. 

Sublimation - This is when water moves directly to vapor from ice or snow without ever melting into water. Good conditions for sublimation to occur is when ice or snow is in very cold conditions, but it is windy and the sun is shining. 

Transpiration - Transpiration is when plants release water on to their leaves that then evaporates into vapor. Plants will release a lot of water as they grow. Around 10 percent of the water vapor in the atmosphere is estimated to come from transpiration. 

Water in the atmosphere 

We see water in the atmosphere in the form of clouds. There is a small amount of water even in clear skies, but clouds are where water has started to condense. Condensation is the process of water vapor becoming liquid water. Condensation is a major step in the water cycle. The atmosphere helps to move water around the world. It takes water that evaporated from the ocean and moves it over land where clouds and storms form to water plants with rain. 

Precipitation 

Precipitation is when water falls from the atmosphere back to land. Once enough water gathers in a cloud droplets of water will form and fall to the earth. Depending on the temperature and weather this could be rain, snow, sleet, or even hail. 

Water storage 

A lot of the Earth's water does not take part in the water cycle very often., Much of it is stored. The Earth stores water in a number of places. The ocean is the largest storage of water. Around 96 percent of the Earth's water is stored in the ocean. We can't drink the salty ocean water, so fortunately for us, freshwater is also stored in lakes, glaciers, snow caps, rivers, and below the ground in ground water storage. 

Composition of the Earth

It may seem like the Earth is made up of one big solid rock, but it's really made up of a number of parts. Some of them constantly moving! 

You can think of the Earth as being made up of a number of layers, sort of like an onion. These layers get more and more dense the closer to the center of the earth you get. See the picture below to see the four main layers of the earth: the crust, mantle, outer core, and inner core. 

Crust 

The crust is the thin outer later of the Earth where we live. Well, it looks thin on the picture and it is thin relative to the other layers, but don't worry, we're not going to fall through by accident anytime soon. The crust varies from around 5km thick (in the ocean floor) to around 70km thick (on land where we live called the continental crust). The continental crust is made up of rocks that consist primarily of silica and alumina called the "sial". 

Mantle 

The next layer of the Earth is called the mantle. The mantle is much thicker than the crust at almost 3000km deep. It's made up of slightly different silicate rocks with more magnesium and iron. 

Tectonic plates 

The tectonic plates are a combination of the crust and the outer mantle, also called the lithosphere. These plates move very slowly, around a couple of inches a year. Where the plates touch each other is called a fault. When the plates move and the boundaries bump up against each other it can cause an earthquake. 

Outer Core 

The Earth's outer core is made up of iron and nickel and is very hot (4400 to 5000+ degrees C). This is so hot that the iron and nickel metals are liquid! The outer core is very important to earth as it creates something called a magnetic field. The magnetic field the outer core creates goes way out in to space and makes a protective barrier around the earth that shields us from the sun's damaging solar wind. 

Inner Core 

The Earth's inner core is made up of iron and nickel, just like the outer core, however, the inner core is different. The inner core is so deep within the earth that it's under immense pressure. So much pressure that, even though it is so hot, it is solid. The inner core is the hottest part of the Earth, and, at over 5000 degrees C, is about as hot as the surface of the sun. 

The Earth is unlike every other planet in the Solar System in a number of different ways.

• It is the only planet that has an atmosphere containing 21 percent oxygen.
   
• It is the only planet that has liquid water on its surface.
   
• It is the only planet in the solar system that has life.
   
• The Earth is the only inner planet (Mercury, Venus, Earth and Mars) to have one large satellite, the Moon.  Mars has two very tiny moons.  Mercury and Venus have none.
   
• The Earth is fragile.  Its surface is split into plates (tectonic plates) which float on a rocky mantle – the layer between the surface of the earth, its crust, and its hot liquid core.  The inside of the Earth is active andearthquakes, volcanoes and mountain building takes place along the boundaries of the tectonic plates. 
• When viewed from outer space much of the Earth’s surface cannot be seen because of clouds of water vapour.  The water vapour makes the Earth, when seen from outside, into a brilliant shining orb, as you can see in Figure 1.
• The Earth is the third planet from the Sun and comes between the planet Venus and the planet Mars.
 
Figure 2. The planets of the Solar System.
• The Earth takes 365¼ days to complete its orbit round the Sun.  The Earth’s year is therefore 365 days long but the ¼ days are added up and every fourth year has one extra day, on the 29th of February.  This fourth year is called a Leap Year (366 days) and is always a year which can be divided exactly by 4 – 2000, 2004, 2008, 2012, 2016.
• The planets closer to the Sun, Mercury and Venus, have shorter years than the Earth.  The planets further away from the Sun have longer years; Pluto takes 249 of our years to make one orbit of the Sun.
   
• As the Earth orbits round the Sun it turns on its axis, rotating right round in 24 hours.  The side of the Earth that faces the Sun has daytime and the side of the Earth that is turned away from the Sun has night-time.  When it is daytime in Britain, it is night-time on the opposite side of the Earth in New Zealand.
   
• As the Earth orbits round the Sun it tilts very slightly and so gives us the seasons.  When the Earth has tilted so that the northern half of the Earth is a little away from the Sun, the northern hemisphere (meaning half of the Earth’s sphere) has winter. 

http://www.funenglishgames.com/wordgames/wordsearch.html


This is a fun word search game for all students.

Pyramids

Built in 30 years, the Pyramid at Giza was the tallest building in the world until the beginning of the 20th century. It remains as the last of the Seven Wonders of the Ancient World.

For centuries, they were the tallest structures on the planet. The Pyramids of Giza, built over 4,000 years ago, still stand atop an otherwise flat, sandy landscape.

One of the Seven Wonders of the World, the pyramids defy 21st-century humans to explain their greatest secrets. How could a civilization that lacked bulldozers, forklifts, and trucks build such massive structures? Why would anyone have spent the time and energy to attempt such a task? What treasures were placed inside these monuments?

Accompanying the Pyramids of Giza is, the Sphinx, a gigantic figure of a lion with the head of a pharaoh.

Only a powerful pharaoh could marshal the necessary human resources to build giant pyramids. During the flood seasons, farmers became builders. Huge stone blocks averaging over two tons in weight were mined in quarries and transported to the pyramid site.

Egyptologists theorize that the workers used either rollers or slippery clay to drag the blocks from the quarries to their eventual placement on the pyramid. Construction of the larger pyramids took decades.

Why Pyramids?

Pyramids were built for religious purposes. The Egyptians were one of the first civilizations to believe in an afterlife. They believed that a second self called the ka lived within every human being. When the physical body expired, the ka enjoyed eternal life. Those fortunate enough to pass the test of Osiris wanted to be comfortable in their lives beyond earth. The Great Pyramids were simply grand tombs of powerful pharaohs.

Three pyramids were built at Giza, and many smaller pyramids were constructed around the Nile Valley. The tallest of the Great Pyramids reaches nearly 500 feet into the sky and spans an area greater than 13 acres. The Great Sphinx was sculpted nearby to stand watch over the pyramids. It stands 65 feet tall and consists of a human head atop the body of a lion.

Many believe that the Sphinx was a portrait of King Chefren (Khafret), who was placed in the middle Pyramid. The lion symbolized immortality.

You Can Take It with You

Egyptians who ranked high in status often wanted to take their most prized possessions with them in death, so the ka could enjoy them in its next life. Gold, silver, and bronze artifacts were loaded into the interiors of the great tombs. Fine linens and artwork adorned the secret chambers.

In the early days, dead nobles were often interned with their living slaves and animals. Because this practice eventually proved too costly, artists instead depicted scenes of human activity on the inside walls. Some pyramids were even equipped with a rest room for the pharaoh.

Inside pyramids such as this one for King Pepi I, passageways lead to a main burial chamber. Designs varied for each pyramid.

Great precautions were taken to protect the tombs from looters. Egyptians believed that a defiler of a pharaoh's resting place would be cursed for eternity. The entrance to the inner chambers was carefully hidden. The pharaoh's mummy was placed in a huge coffin called a sarcophagus, which was made of the hardest known stone blocks. But despite such warnings and precautions, tombs were raided over the years by grave robbers.

The pyramids, however, have stood the test of time. Although their outer limestone layers have long since been stripped or passed into dust, the pyramids still stand. About 80 dot the horizons of modern Egypt. They remain as time capsules cast forward by a once-great civilization.

Early Civilization in the Indus Valley

Aryans probably used the Khyber Pass to cross the mountains during their Indian invasion. Located in present day Pakistan, the pass is about 16 yards wide at its narrowest point.

The phrase "early civilizations" usually conjures up images of Egypt and Mesopotamia, and their pyramids, mummies, and golden tombs.

But in the 1920s, a huge discovery in South Asia proved that Egypt and Mesopotamia were not the only "early civilizations." In the vast Indus River plains (located in what is today Pakistan and western India), under layers of land and mounds of dirt, archaeologists discovered the remains of a 4,600 year-old city. A thriving, urban civilization had existed at the same time as Egyptian and Mesopotamian states — in an area twice each of their sizes.

The people of this Indus Valley civilization did not build massive monuments like their contemporaries, nor did they bury riches among their dead in golden tombs. There were no mummies, no emperors, and no violent wars or bloody battles in their territory.

Remarkably, the lack of all these is what makes the Indus Valley civilization so exciting and unique. While others civilizations were devoting huge amounts of time and resources to the rich, the supernatural, and the dead, Indus Valley inhabitants were taking a practical approach to supporting the common, secular, living people. Sure, they believed in an afterlife and employed a system of social divisions. But they also believed resources were more valuable in circulation among the living than on display or buried underground.

Copyright J.M. Kenoyer/www.harappa.com

The "Great Bath" of Mohenjo-Daro is the earliest known public water tank of the ancient world. Most scholars believe that this tank would have been used in conjunction with religious ceremonies.

Amazingly, the Indus Valley civilization appears to have been a peaceful one. Very few weapons have been found and no evidence of an army has been discovered.

Excavated human bones reveal no signs of violence, and building remains show no indication of battle. All evidence points to a preference for peace and success in achieving it.

So how did such a practical and peaceful civilization become so successful?

The Twin Cities

Photo courtesy of Carolyn Brown Heinz

Seals such as these were used by merchants in the Harappan civilization. Many experts believe that they signified names.

The ruins of two ancient cities, Harappa and Mohenjo-Daro (both in modern-day Pakistan), and the remnants of many other settlements, have revealed great clues to this mystery. Harappa was, in fact, such a rich discovery that the Indus Valley Civilization is also called the Harappan civilization.

The first artifact uncovered in Harappa was a unique stone seal carved with a unicorn and an inscription. Similar seals with different animal symbols and writings have since been found throughout the region. Although the writing has not yet been deciphered, the evidence suggests they belonged to the same language system. Apparently, Mesopotamia's cuneiform system had some competition in the race for the world's first script.

The discovery of the seals prompted archaeologists to dig further. Amazing urban architecture was soon uncovered across the valley and into the western plains. The findings clearly show that Harappan societies were well organized and very sanitary.

This copy of the Rig Veda was written after the Vedic Age. The Aryans had no form of writing at the time they invaded India. Instead, these religious scripts would have been memorized and passed down orally by Brahman priests.

For protection from seasonal floods and polluted waters, the settlements were built on giant platforms and elevated grounds. Upon these foundations, networks of streets were laid out in neat patterns of straight lines and right angles. The buildings along the roads were all constructed of bricks that were uniform in size.

The brick houses of all city dwellers were equipped with bathing areas supplied with water from neighborhood wells. Sophisticated drainage systems throughout the city carried dirty water and sewage outside of living spaces. Even the smallest houses on the edges of the towns were connected to the systems — cleanliness was obviously of utmost importance.

The Fall of Harappan Culture

No doubt, these cities were engineering masterpieces of their time. The remains of their walls yield clues about the culture that thrived in the Indus Valley. Clay figurines of goddesses, for example, are proof that religion was important. Toys and games show that even in 3000 B.C.E., kids — and maybe even adults — liked to play. Pottery, textiles, and beads are evidence of skilled craftsmanship and thriving trade.

The swastika was a sacred symbol for the Aryans signifying prosperity. The word comes from the Sanskrit for "good fortune." Hitler borrowed the symbol, changed the angle and direction of the arms, and used it to represent the Nazis.

It was this intensive devotion to craftsmanship and trade that allowed the Harappan culture to spread widely and prosper greatly. Each time goods were traded or neighbors entered the gates of the cities to barter, Indus culture was spread.

Eventually, though, around 1900 B.C.E, this prosperity came to an end. The integrated cultural network collapsed, and the civilization became fragmented into smaller regional cultures. Trade, writing, and seals all but disappeared from the area.

Many believe that the decline of the Harappan civilization was a result of Aryan invasions from the north. This theory seems logical because the Aryans came to power in the Ganges Valley shortly after the Indus demise of the Indus Valley Civilization. Because there is little evidence of any type of invasion though, numerous historians claim that it was an environmental disaster that led to the civilization's demise. They argue that changing river patterns disrupted the farming and trading systems and eventually led to irreparable flooding.

Although the intricate details of the early Indus Valley culture might never be fully known, many pieces of the ancient puzzle have been discovered. The remains of the Indus Valley cities continue to be unearthed and interpreted today. With each new artifact, the history of early Indian civilization is strengthened and the legacy of this ingenious and diverse metropolis is made richer.