What Is Earth Pdf

[Brook Mithani]

Earth is our home planet. Scientists believe Earth and its moon formed around the same time as the rest of the solar system. They think that was about 4.5 billion years ago. Earth is the fifth-largest planet in the solar system. Its diameter is about 8,000 miles. And Earth is the third-closest planet to the sun. Its average distance from the sun is about 93 million miles. Only Mercury and Venus are closer.

The equator is an imaginary circle that divides Earth into two halves. The northern half is called the Northern Hemisphere. The southern half is called the Southern Hemisphere. The northernmost point on Earth is called the North Pole. The southernmost point on Earth is called the South Pole.

At all times, half of Earth is lighted by the sun and half is in darkness. Areas facing toward the sun experience daytime. Areas facing away from the sun experience nighttime. As the planet spins, most places on Earth cycle through day and night once every 24 hours. The North Pole and South Pole have continuous daylight or darkness depending on the time of year.

Earth consists of land, air, water and life. The land contains mountains, valleys and flat areas. The air is made up of different gases, mainly nitrogen and oxygen. The water includes oceans, lakes, rivers, streams, rain, snow and ice. Life consists of people, animals and plants. There are millions of species, or kinds of life, on Earth. Their sizes range from very tiny to very large.

Information gathered by NASA satellites helps scientists predict weather and climate. It also helps public health officials track disease and famine. It helps farmers decide when to plant crops and what kinds to plant. And it helps emergency workers respond to natural disasters.

The Division of Earth Sciences supports proposals for research geared toward improving the understanding of the structure, composition, and evolution of the Earth, the life it supports, and the processes that govern the formation and behavior of the Earth's materials. The results of this research will create a better understanding of the Earth's changing environments, and the natural distribution of its mineral, water, biota, and energy resources and provide methods for predicting and mitigating the effects of geologic hazards such as earthquakes, volcanic eruptions, floods, landslides.

Earth science is the study of the Earth's structure, properties, processes, and four and a half billion years of biotic evolution. Understanding these phenomena is essential to maintenance of life on the planet. The expanding world population demands more resources; faces increasing losses from natural hazards; and releases more pollutants to the air, water, and land. Sustaining our existence requires scientific understanding of the natural materials and processes linking the geosphere, hydrosphere, atmosphere, and biosphere. Life prospers or fails at the surface of the Earth where these environments intersect.

The knowledge gained and the services provided by earth scientists help society cope with its environment in many ways. Their knowledge about the structure, stratigraphy, and chemical composition of the earth's crust helps us locate resources that sustain and advance our quality of life. Understanding the forces in the crust, and the natural processes on the surface allows us to anticipate natural disasters such as volcanoes and earthquakes, and geologic environments, such as damaging mining practices or improper waste disposal, gives us information to correct such practices and design more benign procedures for the future. Finally, a comprehensive perception of planetary physics will allow us to anticipate major changes in global environmental conditions and control or acclimate to those changes.

In general use, the term "earth science" often includes the study of the earth's atmosphere (meteorology or atmospheric science), the water flowing on and beneath the surface of continents (hydrology), and the earth's seas and oceans (oceanography or ocean sciences). The NSF organizational taxonomy defines earth science as including the fields of "solid-earth" science (geology, geochemistry, and geophysics (plus continental hydrology. It excludes the "fluid-earth" sciences of oceanography and atmospheric science, which have their own respective divisions in the organization, and are covered in other reports in this series. The NSF Division of Earth Sciences is part of the Geosciences Directorate that also includes the divisions of Atmospheric Sciences and Ocean Sciences. The term "geosciences" is similarly used to represent only the "solid-earth" sciences or solid and fluid sciences depending on the context, so care must be always exercised when interpreting data regarding the earth science fields from various sources.

From what we know so far, Earth is the only planet that hosts life and the only one in the Solar System with liquid water on the surface. Earth is also the only planet in the solar system with active plate tectonics, where the surface of the planet is divided into rigid plates that collide and move apart, causing earthquakes, mountain building, and volcanism. Sites of volcanism along Earth's submarine plate boundaries are considered to be potential environments where life could have first emerged.

Earth is the right distance from the sun, such that liquid water has been stable in significant volumes over much of the planet's lifetime. It has the right chemical ingredients for life (e.g. water and carbon), and chemical cycling (such as between the planet's interior and oceans by volcanism and other geological activity) provides chemical pathways for life to extract energy to survive.

No. Mercury has no atmosphere and it has an old surface covered in impact craters, so it is very unlike Earth. One similarity is that Mercury and Earth both have internally generated magnetic fields. Venus and Earth are very similar in size. There is emerging evidence for active volcanism on Venus, however, its atmosphere is up to 100 times denser than Earth's and is mostly carbon dioxide with sulfuric acid clouds. The surface of Saturn's moon Titan physically resembles Earth's, with mountains, rivers, lakes, and seas. The difference is that Titan's mountains are made from water ice, which is as strong as rock under its surface temperature (-180C), and the rivers and seas are full of hydrocarbons.

Scientists estimated that 1 in 5 stars like our sun has one Earth-like planet orbiting around them, which may support life. Considering that there are more than 200 billion stars in our Milky Way, there might be an estimated 40 billion planets that might support life in our galaxy.

Earth observation from space provides objective coverage across both space and time. The same space-based sensor gathers data from sites across the world, including places too remote or otherwise inaccessible for ground-based data acquisition.

And because Earth observation satellites remain in place for long periods of time, they can highlight environmental changes occurring gradually. Looking back through archived satellite data shows us the steady clearing of the world's rainforests, an apparent annual rise in sea level approaching 2 mm a year, and the increase of atmospheric pollution.

Earth is the only naturally habitable planet for complex (e.g. human) life in the solar system. The consequences of a warming climate are far-reaching and are already threatening some people's ways of life and damaging wider biodiversity. If Earth becomes uninhabitable we have nowhere else to go. Colonizing the Moon and Mars is no substitute for preserving Earth. The Moon and Mars cannot sustain Earth's population of humans and other organisms.

Earth, our home, is the third planet from the sun. While scientists continue to hunt for clues of life beyond Earth, our home planet remains the only place in the universe where we've ever identified living organisms.

Earth has a diameter of roughly 8,000 miles (13,000 kilometers) and is mostly round because gravity generally pulls matter into a ball. But the spin of our home planet causes it to be squashed at its poles and swollen at the equator, making the true shape of the Earth an "oblate spheroid."

Our planet is unique for many reasons, but its available water and oxygen are two defining features. Water covers roughly 71% of Earth's surface, with most of that water located in our planet's oceans. About a fifth of Earth's atmosphere consists of oxygen, produced by plants.

Earth's axis of rotation is tilted in relation to the ecliptic plane, an imaginary surface through the planet's orbit around the sun. This means the Northern and Southern Hemispheres will sometimes point toward or away from the sun depending on the time of year, and this changes the amount of light the hemispheres receive, resulting in the changing seasons.

Earth happens to orbit the sun within the so-called "Goldilocks zone," where temperatures are just right to maintain liquid water on our planet's surface. Earth's orbit is not a perfect circle, but rather a slightly oval-shaped ellipse, similar to the orbits of all the other planets in our solar system. Our planet is a bit closer to the sun in early January and farther away in July, although this proximity has a much smaller effect on the temperatures we experience on the planet's surface than does the tilt of Earth's axis.

Scientists think Earth was formed at roughly the same time as the sun and other planets some 4.6 billion years ago when the solar system coalesced from a giant, rotating cloud of gas and dust known as the solar nebula. As the nebula collapsed under the force of its own gravity, it spun faster and flattened into a disk. Most of the material in that disk was then pulled toward the center to form the sun.

"It was thought that because of these asteroids and comets flying around colliding with Earth, conditions on early Earth may have been hellish," Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colorado, previously told Space.com.

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