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Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth .
Table of contents
- NASA to build telescope for detecting asteroids that threaten Earth | Science | AAAS
- Structure and Surface
- Mysterious Mineral from Earth's Mantle Discovered in South African Diamond
Continental crust averages some 25 miles 40 km thick, although it can be thinner or thicker in some areas. Oceanic crust is usually only about 5 miles 8 km thick. Water fills in low areas of the basalt crust to form the world's oceans. Earth gets warmer toward its core. At the bottom of the continental crust, temperatures reach about 1, degrees Fahrenheit 1, degrees Celsius , increasing about 3 degrees F per mile 1 degree C per km below the crust. Geologists think the temperature of Earth's outer core is about 6, to 7, degrees F 3, to 4, degrees C and that the inner core may reach 12, degrees F 7, degrees C — hotter than the surface of the sun.
Earth's magnetic field is generated by currents flowing in Earth's outer core. The magnetic poles are always on the move, with the magnetic North Pole accelerating its northward motion to 24 miles 40 km annually since tracking began in the s. It will likely exit North America and reach Siberia in a matter of decades. Earth's magnetic field is changing in other ways, too.
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Globally, the magnetic field has weakened 10 percent since the 19th century , according to NASA. These changes are mild compared to what Earth's magnetic field has done in the past. A few times every million years or so, the field completely flips, with the North and the South poles swapping places.
The magnetic field can take anywhere from to 3, years to complete the flip. The strength of Earth's magnetic field decreased by about 90 percent when a field reversal occurred in ancient past, according to Andrew Roberts, a professor at the Australian National University. The drop makes the planet more vulnerable to solar storms and radiation, which can could significantly damage satellites and communication and electrical infrastructure. When charged particles from the sun get trapped in Earth's magnetic field, they smash into air molecules above the magnetic poles, causing them to glow.
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This phenomenon is known as the aurorae , the northern and southern lights. Nowhere else in the solar system is there an atmosphere loaded with free oxygen, which is vital to one of the other unique features of Earth: life. Air surrounds Earth and becomes thinner farther from the surface.
Roughly miles km above Earth, the air is so thin that satellites can zip through the atmosphere with little resistance. Still, traces of atmosphere can be found as high as miles km above the planet's surface. The lowest layer of the atmosphere is known as the troposphere, which is constantly in motion and why we have weather. Sunlight heats the planet's surface, causing warm air to rise into the troposphere. This air expands and cools as air pressure decreases, and because this cool air is denser than its surroundings, it then sinks and gets warmed by the Earth again.
Above the troposphere, some 30 miles 48 km above the Earth's surface, is the stratosphere. The still air of the stratosphere contains the ozone layer, which was created when ultraviolet light caused trios of oxygen atoms to bind together into ozone molecules. Ozone prevents most of the sun's harmful ultraviolet radiation from reaching Earth's surface, where it can damage and mutate life. Water vapor, carbon dioxide and other gases in the atmosphere trap heat from the sun, warming Earth.
Without this so-called " greenhouse effect ," Earth would probably be too cold for life to exist, although a runaway greenhouse effect led to the hellish conditions now seen on Venus. Earth-orbiting satellites have shown that the upper atmosphere actually expands during the day and contracts at night due to heating and cooling.
The second most abundant element is silicon , at 27 percent, followed by aluminum , at 8 percent; iron , at 5 percent; calcium , at 4 percent; and sodium , potassium and magnesium , at about 2 percent each.
NASA to build telescope for detecting asteroids that threaten Earth | Science | AAAS
The mantle is made of iron and magnesium-rich silicate rocks. The combination of silicon and oxygen is known as silica, and minerals that contain silica are known as silicate minerals. Earth's moon is 2, miles 3, km wide, about one-fourth of Earth's diameter. Our planet has one moon, while Mercury and Venus have none and all the other planets in our solar system have two or more.
The leading explanation for how Earth's moon formed is that a giant impact knocked the raw ingredients for the moon off the primitive, molten Earth and into orbit. Scientists have suggested that the object that hit the planet had roughly 10 percent the mass of Earth, about the size of Mars.
Structure and Surface
Mysterious Mineral from Earth's Mantle Discovered in South African Diamond
Date 6 hours 12 hours 1 day 3 days all. Last day 1 week 1 month all. Microplastics in the Great Lakes: Becoming benthic From the Great Pacific garbage patch to inland rivers, plastics are among the most widespread contaminants on Earth. Is theory on earth's climate in the last 15 million years wrong?
Earth Sciences. Climate experts say they hear talk at UN but not much action Leader after leader told the United Nations on Monday that they will do more to prevent a warming world from reaching even more dangerous levels. Why are mountains so high? Machu Picchu: Ancient Incan sanctuary intentionally built on faults The ancient Incan sanctuary of Machu Picchu is considered one of humanity's greatest architectural achievements. Russia joins Paris climate accord Russia's prime minister on Monday gave formal support to the Paris climate agreement, just hours ahead of a key summit trying to tackle ever increasing gas emissions.
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New evidence of the Sahara's age The Sahara Desert is vast, generously dusty, and surprisingly shy about its age. Can machine learning reveal geology humans can't see? Promoting earth's legacy delivers local economic benefits For iconic landscapes such as Grand Canyon or the Appalachian Mountains, geological features are an integral part of their appeal. Faults' hot streaks and slumps could change earthquake hazard assessments For more than a century, a guiding principle in seismology has been that earthquakes recur at semi-regular intervals according to a "seismic cycle.
The ocean's plastic problem is closer to home than scientists first thought You're probably used to hearing that the ocean is full of plastic, but scientists are puzzled by a rather different problem—there actually appears to be a lot less of it than there should be. Wildfire can pose risks to reservoirs Over the past 30 years, wildfires have gotten bigger, stronger, and occurred more often.
California, China to team up on climate research institute As tensions between China and the United States ratchet up, former California Gov. We've learned a great deal since South Africa's biggest quake 50 years ago Fifty years ago I was a teenager growing up in Cape Town. NASA satellite identified a less-organized Caribbean Tropical Storm Karen Satellite imagery can be used to peer inside a storm as well as assess the storm's outside shape to give forecasters understanding of what's happening to it.
Sustainable dairy project finds ways to lower emissions, boost profits A six-year-long, nationwide research project has concluded with solutions to help the dairy industry reduce greenhouse gas emissions while boosting profitability. Featured Last Comments Popular Partners New technique to improve ductility of ceramic materials for missiles, engines 22 minutes ago. More news Earth Sciences. Other news Materials Science. General Physics. Quantum Physics. Condensed Matter. Social Sciences.
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