For other uses, see Homework (disambiguation).
Homework, or a homework assignment, is a set of tasks assigned to students by their teachers to be completed outside the class. Common homework assignments may include a quantity or period of reading to be performed, writing or typing to be completed, math problems to be solved, material to be reviewed before a test, or other skills to be practiced.
The effect of homework is debated. Generally speaking, homework does not improve academic performance among children and may improve academic skills among older students. It also creates stress for students and their parents and reduces the amount of time that students could spend outdoors, exercising, playing sports, working, sleeping or in other activities.
The basic objectives of assigning homework to students are the same as schooling in general: to increase the knowledge and improve the abilities and skills of the students, to prepare them for upcoming (or complex or difficult) lessons, to extend what they know by having them apply it to new situations, or to integrate their abilities by applying different skills to a single task. Homework also provides an opportunity for parents to participate in their children's education. Homework is designed to reinforce what students have already learned.
Teachers have many purposes for assigning homework including:
- personal development,
- parent–child relations,
- parent–teacher communications,
- peer interactions,
- public relations, and
Homework research dates back to the early 1900s. However, no consensus exists on the general effectiveness on homework. Results of homework studies vary based on multiple factors, such as the age group of those studied and the measure of academic performance.
Among teenagers, students who spend somewhat more time on homework generally have higher grades, and somewhat higher test scores than students who spend less time on homework. Very high amounts of homework cause students' academic performance to worsen, even among older students. Students who are assigned homework in middle and high school score somewhat better on standardized tests, but the students who have 60 to 90 minutes of homework a day in middle school or more than 2 hours in high school score worse.
However, younger students who spend more time on homework generally have slightly worse, or the same academic performance than those who spend less time on homework. Homework does not improve academic achievements for grade school students.
Low-achieving students receive more benefit from doing homework than high-achieving students. However, schoolteachers commonly assign less homework to the students who need it most, and more homework to the students who are performing well.
The amount of homework given does not necessarily affect students' attitudes towards homework and various other aspects of school.
Epstein (1988) found a near-zero correlation between the amount of homework and parents' reports on how well their elementary school students behaved. Vazsonyi & Pickering (2003) studied 809 adolescents in American high schools, and found that, using the Normative Deviance Scale as a model for deviance, the correlation was r = .28 for Caucasian students, and r = .24 for African-American students. For all three of the correlations, higher values represent a higher correlation between time spent on homework and poor conduct.
Bempechat (2004) says that homework develops students' motivation and study skills. In a single study, parents and teachers of middle school students believed that homework improved students' study skills and personal responsibility skills. Their students were more likely to have negative perceptions about homework and were less likely to ascribe the development of such skills to homework.Leone & Richards (1989) found that students generally had negative emotions when completing homework and reduced engagement compared to other activities.
Health and daily life
Homework has been identified in numerous studies and articles as a dominant or significant source of stress and anxiety for students. Studies on the relation between homework and health are few compared to studies on academic performance.
Cheung & Leung-Ngai (1992) surveyed 1,983 students in Hong Kong, and found that homework led not only to added stress and anxiety, but also physical symptoms, such as headaches and stomachaches. Students in the survey who were ridiculed or punished by parents and peers had a higher incidence of depression symptoms, with 2.2% of students reporting that they "always" had suicidal thoughts, and anxiety was exacerbated by punishments and criticism of students by teachers for both problems with homework as well as forgetting to hand in homework.
A 2007 study of American students by MetLife found that 89% of students felt stressed from homework, with 34% reporting that they "often" or "very often" felt stressed from homework. Stress was especially evident among high school students. Students that reported stress from homework were more likely to be deprived of sleep.
Homework can cause tension and conflict in the home as well as at school, and can reduce students' family and leisure time. In the Cheung & Leung-Ngai (1992) survey, failure to complete homework and low grades where homework was a contributing factor was correlated with greater conflict; some students have reported teachers and parents frequently criticizing their work. In the MetLife study, high school students reported spending more time completing homework than performing home tasks.Kohn (2006) argued that homework can create family conflict and reduce students' quality of life. The authors of Sallee & Rigler (2008), both high school English teachers, reported that their homework disrupted their students' extracurricular activities and responsibilities. However, Kiewra et al. (2009) found that parents were less likely to report homework as a distraction from their children's activities and responsibilities. Galloway, Conner & Pope (2013) recommended further empirical study relating to this aspect due to the difference between student and parent observations.
Galloway, Conner & Pope (2013) surveyed 4,317 high school students from ten high-performing schools, and found that students reported spending more than 3 hours on homework daily. 72% of the students reported stress from homework, and 82% reported physical symptoms. The students slept an average of 6 hours 48 minutes, lower than the recommendations prescribed by various health agencies.
A study done at the University of Michigan in 2007 concluded that the amount of homework given is increasing. In a sample taken of students between the ages of 6 and 9 years, it was shown that students spend more than 2 hours a week on homework, as opposed to 44 minutes in 1981.
Some educators argue that homework is beneficial to students, as it enhances learning, develops the skills taught in class, and lets educators verify that students comprehend their lessons. Proponents also argue that homework makes it more likely that students will develop and maintain proper study habits that they can use throughout their educational career.
Historically, homework was frowned upon in American culture. With few students interested in higher education, and due to the necessity to complete daily chores, homework was discouraged not only by parents, but also by school districts. In 1901, the California legislature passed an act that effectively abolished homework for those who attended kindergarten through the eighth grade. But, in the 1950s, with increasing pressure on the United States to stay ahead in the Cold War, homework made a resurgence, and children were encouraged to keep up with their Russian counterparts. By the end of the Cold War in the early 1990s, the consensus in American education was overwhelmingly in favor of issuing homework to students of all grade levels.
British students get more homework than many other countries in Europe. The weekly average for the subject is 5 hours. The main distinction for UK homework is the social gap, with middle-class teenagers getting a disproportionate amount of homework compared to Asia and Europe.
In 2012, a report by the OECD showed that Spanish children spend 6.4 hours a week on homework. This prompted the CEAPA, representing 12,000 parent associations to call for a homework strike.
Notes and references
Effectiveness of homework
- Cooper, Harris; Robinson, Jorgianne C.; Patall, Erika A. (2006). "Does Homework Improve Academic Achievement? A Synthesis of Research, 1987-2003". Review of Educational Research. 76 (1): 1–62. doi:10.3102/00346543076001001.
- Epstein, Joyce L. (1988), "Homework practices, achievements, and behaviors of elementary school students", Center for Research on Elementary and Middle Schools
- Trautwein, Ulrich; Köller, Olaf (2003). "The Relationship Between Homework and Achievement—Still Much of a Mystery". Educational Psychology Review. 15 (2): 115–145. doi:10.1023/A:1023460414243.
- Vazsonyi, Alexander T.; Pickering, Lloyd E. (2003). "The Importance of Family and School Domains in Adolescent Deviance: African American and Caucasian Youth". Journal of Youth and Adolescence. 32 (2): 115–128. doi:10.1023/A:1021857801554.
Homework and non-academic effects
- Bauwens, Jeanne; Hourcade, Jack J. (1992). "School-Based Sources of Stress Among Elementary and Secondary At-Risk Students". The School Counselor. 40 (2): 97–102.
- Bempechat, Janine (2004). "The Motivational Benefits of Homework: A Social-Cognitive Perspective". Theory In Practice. 43 (3): 189–196. doi:10.1353/tip.2004.0029.
- Cheung, S. K.; Leung-Ngai, J. M. Y. (1992). "Impact of homework stress on children's physical and psychological well-being"(PDF). Journal of the Hong Kong Medical Association. 44 (3): 146–150.
- Conner, Jerusha; Pope, Denise; Galloway, Mollie (2009). "Success with Less Stress". Health and Learning. 67 (4): 54–58.
- Cooper, Robinsin & Patall (2006, pp. 46–48)
- Galloway, Mollie; Conner, Jerusha; Pope, Denise (2013). "Nonacademic Effects of Homework in Privileged, High-Performing High Schools". The Journal of Experimental Education. 81 (4): 490–510. doi:10.1080/00220973.2012.745469.
- Hardy, Lawrence (2003). "Overburdened, Overwhelmed". American School Board Journal. 190: 18–23.
- Kiewra, Kenneth A; Kaufman, Douglas F.; Hart, Katie; Scoular, Jacqui; Brown, Marissa; Keller, Gwendolyn; Tyler, Becci (2009). "What Parents, Researchers, and the Popular Press Have to Say About Homework". scholarlypartnershipsedu. 4 (1): 93–109.
- Kouzma, Nadya M.; Kennedy, Gerard A. (2002). "Homework, stress, and mood disturbance in senior high school students"(PDF). Psychological Reports. 91 (1): 193–198. doi:10.2466/pr0.2002.91.1.193. PMID 12353781.
- Leone, Carla M.; Richards, H. (1989). "Classwork and homework in early adolescence: The ecology of achievement". Journal of Youth and Adolescence. 18 (6): 531–548. doi:10.1007/BF02139072. PMID 24272124.
- Markow, Dana; Kim, Amie; Liebman, Margot (2007), The MetLife Survey of the American Teacher: The homework experience(PDF), Metropolitan Life Insurance Foundation
- Sallee, Buffy; Rigler, Neil (2008). "Doing Our Homework on Homework: How Does Homework Help?". The English Journal. 98 (2): 46–51.
- West, Charles K.; Wood, Edward S. (1970). "Academic Pressures on Public School Students". Educational Leadership. 3 (4): 585–589.
- Xu, Jianzhong; Yuan, Ruiping (2003). "Doing homework: Listening to students', parents', and teachers' voices in one urban middle school community". School Community Journal. 13 (2): 25–44.
- Ystgaard, M. (1997). "Life stress, social support and psychological distress in late adolescence". Social Psychiatry and Psychiatric Epidemiology. 32 (5): 277–283. doi:10.1007/BF00789040. PMID 9257518.
- Duke Study: Homework Helps Students Succeed in School, As Long as There Isn't Too Much
- The Case Against Homework: How Homework Is Hurting Our Children and What We Can Do About It by Sarah Bennett & Nancy Kalish (2006) Discusses in detail assessments of studies on homework and the authors' own research and assessment of the homework situation in the United States. Has specific recommendations and sample letters to be used in negotiating a reduced homework load for your child.
- Closing the Book on Homework: Enhancing Public Education and Freeing Family Time by John Buell (2004)
- The Battle Over Homework: Common Ground for Administrators, Teachers, and Parents by Harris Cooper (2007)
- The Homework Myth: Why Our Kids Get Too Much of a Bad Thing by Alfie Kohn (2006)
- The End of Homework: How Homework Disrupts families, Overburdens Children, and Limits Learning by Etta Kralovec and John Buell (2000)
|Look up homework in Wiktionary, the free dictionary.|
|Wikimedia Commons has media related to Homework.|
- ^Synthesis of research on homework. H Cooper - Educational leadership, 1989 - addison.pausd.org
- ^Needlmen, Robert. "Homework: The Rules of the Game".
- ^Epstein, Joyce L.; Voorhis, Frances L. Van (2001-09-01). "More Than Minutes: Teachers' Roles in Designing Homework". Educational Psychologist. 36 (3): 181–193. doi:10.1207/S15326985EP3603_4. ISSN 0046-1520.
- ^Wallis, Claudia (August 29, 2006). "The Myth About Homework". Time Online.
- ^ abCoughlan, Sean (2016-09-28). "Is homework worth the hassle?". BBC News. Retrieved 2017-04-21.
- ^Bauwens & Hourcade (1992), Conner & Denise (2009), Hardy (2003), Kouzma & Kennedy (2002), West & Wood (1970), Ystgaard (1997).
- ^Seligman, Katherine (1999-12-19). "Parents: Too much homework". Hearst Communications Inc. Retrieved 2013-06-03.
- ^ abGrohnke, Kennedy, and Jake Merritt. "Do Kids Need Homework?" ScholasticNews/ Weekly Reader Edition 5/6, vol. 85, no. 3, 2016, pp. 7.
- ^"History of Homework". The San Francisco Chronicle. 1999-12-20. Retrieved 2007-03-24.
- ^Coughlan, Sean (11 December 2014). "UK families' 'long homework hours'". Bbc.co.uk. Retrieved 2 November 2017.
- ^Marsh, Sarah (2 November 2016). "Parents in the UK and abroad: do your children get set too much homework?". Theguardian.com. Retrieved 2 November 2017.
Earth seen from a satellite
|Longest distance from the Sun||152,097,701 km|
|Shortest distance from the Sun||147,098,074 km|
|Longest distance from the center of its orbital path|
|How long it takes to complete an orbit||365.256366 days|
|Average speed||29.783 km/s|
|Angle above the reference plane|
to the invariable plane
|Size and other qualities|
|Average radius||6,371.0 km (3,958.8 mi)|
|Surface area||510,072,000 km²|
|Volume||1.08321 × 10¹² km³|
|Mass||5.9736 × 1024 kg|
|Average density||5.515 g/cm³|
|Surface gravity||0.99732 g|
|Escape velocity||11.186 km/s|
|Avg. surface temp.||14°C|
Earth is the planet we live on. It is the third planet from the sun. It is the only planet known to have life on it. Lots of scientists think the earth formed around 4.5 billion years ago. It is one of four rocky planets on the inside of the Solar System. The other three are Mercury, Venus and Mars.
The large mass of the sun makes Earth move around it, just as the mass of Earth makes the moon move around it. Earth also turns around in space, so that different parts face the sun at different times. Earth goes around the sun once (one "year") for every 365¼ times it turns all the way around (one "day").
Earth is the only planet in our solar system that has a large amount of liquidwater. About 71% of the surface of Earth is covered by oceans. Because of this, people sometimes call it "blue planet".
Because of its water, Earth is home to millions of species of plants and animals. The things that live on Earth have changed its surface greatly. For example, early cyanobacteria changed the air and gave it oxygen. The living part of Earth's surface is called the "biosphere".
Orbit and turning[change | change source]
Earth is part of the eight planets and many thousands of small bodies that move around the Sun as its solar system. The Solar System is moving through the Orion Arm of the Milky Waygalaxy now, and will be for about the next 10,000 years.
Earth is generally 150,000,000 kilometers or 93,000,000 miles away from the sun (this distance is named an "Astronomical Unit"). Earth moves along its way at an average speed of about 30 km or 19 mi a second. Earth turns all the way around about 365¼ times in the time it takes for Earth to go all the way around the sun. To make up this extra bit of a day every year, an additional day is used every four years. This is named a "leap year".
The Moon goes around Earth at an average distance of 400,000 kilometers (250,000 mi). It is locked to Earth, so that it always has the same half facing Earth; the other half is called the "dark side of the moon". It takes about 27⅓ days for the Moon to go all the way around Earth, but because Earth is moving around the Sun at the same time, it takes about 29½ days for the Moon to go from dark to bright to dark again. This is where the word "month" came from, even though most months now have 30 or 31 days.
History of Earth[change | change source]
- See also: Historical geology, Age of the Earth, Giant impact hypothesis, and Great Oxygenation Event
Earth and the other planets formed about 4.6 billion years ago. They were made of the leftover gas from the nebula that made the Sun. The Moon may have been formed after a collision between the early Earth and a smaller planet (sometimes called Theia). Scientists believe that parts of both planets broke off — becoming (by gravity) the Moon.
Earth's water came from different places. Condensingwater vapour, and comets and asteroids hitting Earth, made the oceans. Within a billion years (that is at about 3.6 billion years ago) the first lifeevolved, in the Archaeanera. Some bacteria developed photosynthesis, which lets plants make food from the Sun's light and water. This released a lot of oxygen, which was first taken up by iron in solution. Eventually, free oxygen got into the atmosphere or air, making Earth's surface suitable for aerobic life (see Great Oxygenation Event). This oxygen also formed the ozonelayer which protects Earth's surface from bad ultravioletradiation from the Sun. Complex life on the surface of the land did not exist before the ozone layer.
Earth was very different in the distant past. Long ago, almost all land was in one place. This is called a supercontinent. The earliest known supercontinent was called Vaalbara. Much later, there was a time (the Cryogenian) when Earth was almost entirely covered by thick ice sheets (glaciers). This is called the Snowball Earththeory.
What it is made of[change | change source]
Earth is rocky. It is the largest of the rocky planets moving around the sun by mass and by size. It is much smaller than the gas giants such as Jupiter.
Chemical make-up[change | change source]
Overall, Earth is made of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%). The 1.2% left over is made of many different kinds of other chemicals. Chemicals that are very uncommon (such as gold and platinum) can be very valuable.
The structure of Earth changes from the inside to the outside. The center of earth (Earth's core) is mostly iron (88.8%), nickel (5.8%), sulfur (4.5%), and less than 1% other things. The Earth's crust is largely oxygen (47%). Oxygen is normally a gas but it can join with other chemicals to make compounds like water and rocks. 99.22% of rocks have oxygen in them. The most common oxygen-having rocks are silica (made with silicon), alumina (made with aluminium), rust (made with iron), lime (made with calcium), magnesia (made with magnesium), potash (made with potassium), and sodium oxide, and there are others as well.
Shape[change | change source]
Earth's shape is a spheroid: not quite a sphere because it is slightly squashed on the top and bottom. The shape is called an oblate spheroid. As Earth spins around itself, the centrifugal force forces the equator out a little and pulls the poles in a little. The equator, around the middle of Earth's surface, is about 40,075 kilometers or 24,900 miles long.
The highest mountain above sea level—the well-known Mount Everest (which is 8.8 km or 5.5 mi above sea level)—is not actually the one that is the farthest away from the center of the Earth. Instead, the sleeping volcanoMount Chimborazo in Ecuador is; it is only 6.3 km or 3.9 mi above sea level but it is almost at the equator. Because of this, Mount Chimborazo is 6,384.4 km or 3,967.1 mi from the center of the Earth, while Mount Everest is 2.1 kilometers or 1.3 miles closer to it. Similarly, the lowest point below sea level that we are conscious of is the Challenger Deep in the Mariana Trench in the Pacific Ocean. It is about 10.9 km or 6.8 mi below sea level, but, again, there are probably places at the bottom of the Arctic Ocean that are nearer to the center of the Earth.
[change | change source]
The deepest hole ever dug is only about 12.3 kilometers or 7.6 miles. We know something about the inside of the Earth, though, because we can learn things from earthquakes and the times when volcanoeserupt. We are able to see how quickly the shock waves move through Earth in different places.
The inside of Earth is very different from the outside. Almost all of Earth's liquid water is in the seas or close to the surface. The surface also has a lot of oxygen, which comes from plants. Small and simple kinds of life can live far under the surface, but animals and plants only live on the surface or in the seas. The rocks on the surface of Earth (Earth's crust) are well known. They are thicker where there is land, between 30 to 50 km or 19 to 31 mi thick. Under the seas they are sometimes only 6 km or 3.7 mi thick. There are three groups of rocks that make up most of the Earth's crust. Some rock is made when the hot liquid rock comes from inside the earth (igneous rocks); another type of rock is made when sediment is laid down, usually under the sea (sedimentary rocks); and a third kind of rock is made when the other two are changed by very high temperature or pressure (metamorphic rocks). A very few rocks also fall out of the sky (meteorites).
Below the crust is warm and almost-liquid rock that is always moving around (the Earth's mantle). Then, there is a thin liquid layer of heated rock (the outer core). This is very hot: 7,000 °C or 13,000 °F. The middle of the inside of the Earth would be liquid as well but all the weight of the rock above it pushes it back into being solid. This solid middle part (the inner core) is almost all iron. This is what makes the Earth magnetic.
Pieces of the crust form plates[change | change source]
Main article: Plate tectonics
The Earth's crust is solid but made of parts which move very slowly. The thin level of hard rock on the outside of the Earth rests on hot liquid material below it in the deeper mantle. This liquid material moves because it gets heat from the hot center of the earth. The slow movement of the plates is what causes earthquakes, volcanoes and large groups of mountains on the Earth.
There are three ways plates can come together. Two plates can move towards each other ("convergent" plate edges). This can form islands (such as Japan), volcanoes, and high mountain ranges (such as the Andes and Himalayas). Two plates can move away from each other ("divergent" plate edges). This gives the warm liquid rock inside the earth a place to come out. This makes special mountain ranges below the sea or large low lands like Africa's Great Rift Valley. Plates are able to move beside each other as well ("transform" plate edges, such as the San Andreas Fault). This makes their edges crush against each other and makes many shocks as they move.
Surface[change | change source]
The outside of the Earth is not even. There are high places called mountains, and high flat places called plateaus. There are low places called valleys and canyons. For the most part, moving air and water from the sky and seasdamages rocks in high places and breaks them into small pieces. The air and water then move these pieces to lower places. Because of this, the Earth would have been very flat a long time before now. The fundamental cause of the differences in the Earth's surface is plate tectonics.
All places on Earth are made of, or are on top of, rocks. The outside of the Earth is usually not uncovered rock. Over 70% of the Earth is covered by seas full of salty water. This salty water makes up about 97½% of all Earth's water. The fresh water people can drink is mostly ice. Only a very small amount is in rivers and under the Earth for people to drink and use. The air above the Earth stops the water from going away into outer space. Also, much of the land on Earth is covered with plants, or with what is left from earlier living things. Places with very little rain are dry wastes called deserts. Deserts usually have few living things, but life is able to grow very quickly when these wastes have rainfall. Places with large amounts of rain may be large woods. Lately, people have changed the environment of the Earth a great deal.
Air[change | change source]
Main article: Atmosphere
All around the Earth is a large amount of air (the atmosphere). The mass of the Earth pulls the gasses in the air down and does not let them go into outer space. The air is mostly made of nitrogen (about 78%) and oxygen (about 21%) but there are a few other gasses as well. Most living things need the air (or parts of the air gripped in the water) to breathe and live. They use the gasses—especially oxygen and carbon dioxide—to make and use sugar and to give themselves power.
The air animals and plants use to live is only the first level of the air around the Earth (the troposphere). The day to day changes in this level of air are named weather; the changes between places far away from each other and from year to year are named the climate. Rain and storms are both in this level. Both come about because this part of the air gets colder as it goes up. Cold air becomes thicker and falls, and warm air becomes thinner and goes up. The turning Earth moves the air as well and air moves north and south because the middle of the Earth generally gets more power from the Sun and is warmer than the north and south points. At the same time, air over water (specially very warm water) gets water in it but, because cold air is not able to take in as much water, it starts to make clouds and rain as it gets colder. The way water moves around in a circle like this is called the water cycle.
Above this first level, there are four other levels. The air gets colder as it goes up in the first level; in the second level (the stratosphere), the air gets warmer as it goes up. This level has a special kind of oxygen called ozone. The ozone in this air keeps living things safe from damaging rays from the Sun. The power from these rays is what makes this level warmer and warmer. The middle level (the mesosphere) gets colder and colder with height; the fourth level (the thermosphere) gets warmer and warmer; and the last level (the exosphere) is almost outer space and has very little air at all. It reaches about half the way to the Moon. The three outer levels have a lot of electric power moving through them; this is called the ionosphere and is important for radio and other electric waves in the air. It is also where the Northern Lights are.
Even though air seems very light, the weight of all of the air above the outside of the Earth (air pressure) is important. Generally, from sea level to the top of the outer level of the air, a space of air one square centimeter across has a mass of about 1.03 kg and a space of air one square inch across has a weight of about 14.7 pounds. The mass of the air also keeps the Earth safe when rocks (meteorites) hit it from outer space. Without the air, the damage meteorites do would be much greater. Because of the air, meteorites generally burn up long before they get to the earth.
The air also keeps the Earth warm, specially the half turned away from the Sun. Some gasses – especially methane and carbon dioxide – work like a blanket to keep things warm.In the past, the Earth has been much warmer and much colder than it is now. Since people have grown used to the heat we have now, though, we do not want the Earth to be too much warmer or colder. Most of the ways people create electric power use burning kinds of carbon—especially coal, oil, and natural gas. Burning these creates new carbon dioxide and can cause more warming. A large discussion is going on now about what people should do about the Earth's latest warming, which has gone on for about 150 years. So far, this warming has been good for people: plants have grown better and the weather has been better than when it was colder before. Some people who learn about science, though, say that many bad things will possibly come about if the warming goes on.
People[change | change source]
Main article: Human
About seven billion people live on Earth. They live in about 200 different lands called countries. Some (like Russia) are large with many large cities. Others (like the Vatican) are small. The five countries with the most people are China, India, the United States, Indonesia, and Brazil. About 90% of people live in the north half of the world, which has most of the land. Scientists think that people originally came from Africa. Now, 70% of all people do not live in Africa but in Europe and Asia.
People change the Earth in many ways. They have been able to grow plants for food and clothes for about ten thousand years. When there was enough food, they were able to build towns and cities. Near these places, men and women were able to change rivers, bring water to farms, and stop floods (rising water) from coming over their land. People found useful animals and bred them so they were easier to keep.
Related pages[change | change source]
References[change | change source]
- ↑By International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather than for the planet Earth. Cf.Blue, Jennifer (July 5, 2007). "Descriptor Terms (Feature Types)". Gazetteer of Planetary Nomenclature. USGS. Retrieved 2007-07-05.
- ↑ 2.02.12.22.32.4Williams, Dr. David R. "Earth Fact Sheet". NASA. Retrieved 2011-02-03.
- ↑Allen, Clabon Walter; Cox, Arthur N. (2000). Allen's Astrophysical Quantities. Springer. p. 294. ISBN 0387987460.
- ↑Various (2000). David R. Lide, ed. Handbook of Chemistry and Physics (81st ed.). CRC. ISBN 0-8493-0481-4.
- ↑"The age of the Earth in the twentieth century- a problem (mostly) solved". Geological Society, London, Special Publications. Retrieved 2009-07-28.
- ↑"Rover reveals Mars was once wet enough for life". Microsoft. Retrieved 28 July 2009.
- ↑Blue Planet is a poetic title for the Earth used in movies, in cheap paper books, in poetry, and in government reports (such as the European Space Agency's "Exploring the water cycle of the 'Blue Planet'")
- ↑"How many species are there on Earth". Harvard University. Retrieved 2009-07-28.
- ↑Purves, William Kirkwood; et al. (2001). Life, the science of biology. Macmillan. p. 455. ISBN 0716738732.
- ↑"Origins of life on Earth". Space.com. Retrieved 2009-07-28.
- ↑"Earth's location in the Milky Way". NASA. Retrieved 2009-08-06.
- ↑"NASA- an Earth fact sheet". NASA. Retrieved 2009-08-06.
- ↑Staff (2007-08-07). "Useful Constants". International Earth Rotation and Reference Systems Service. Retrieved 2008-09-23.
- ↑Cite error: Invalid tag; no text was provided for refs named .
- ↑Dalrymple, G. Brent (2001). "The age of the Earth in the twentieth century: a problem (mostly) solved". Special Publications, Geological Society of London190 (1): 205–221. doi:10.1144/GSL.SP.2001.190.01.14.
- ↑"Origin of the Moon in a giant impact near the end of the Earth's formation". Nature.com. Retrieved 2009-07-28.
- ↑"Earth life appeared on land 1.5 billion years earlier than previously thought". SpaceRef.com. Retrieved 2009-07-03.