Welcome Guest [Log In] [Register]
Add Reply
Earth
Topic Started: Mar 25 2009, 01:20 AM (106 Views)
ship
Member Avatar
Administrator
Posted Image

Earth is the third planet from the Sun and the fifth largest:

orbit: 149,600,000 km (1.00 AU) from Sun
diameter: 12,756.3 km
mass: 5.972e24 kg


Hardcopy

Planet Earth
Amazing pictures of Earth from space combine useful science and artistic beauty.

Orbit : Nasa Astronauts Photograph the Earth
A beautiful coffee table book. Kids often ask me which is my favorite planet. My answer is always "Earth". This book shows why.

Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. There are, of course, hundreds of other names for the planet in other languages. In Roman Mythology, the goddess of the Earth was Tellus - the fertile soil (Greek: Gaia, terra mater - Mother Earth).

It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet.

Mir and Earth's limb
Mir space station and Earth's limb
Earth, of course, can be studied without the aid of spacecraft. Nevertheless it was not until the twentieth century that we had maps of the entire planet. Pictures of the planet taken from space are of considerable importance; for example, they are an enormous help in weather prediction and especially in tracking and predicting hurricanes. And they are extraordinarily beautiful.

The Earth is divided into several layers which have distinct chemical and seismic properties (depths in km):

0- 40 Crust
40- 400 Upper mantle
400- 650 Transition region
650-2700 Lower mantle
2700-2890 D'' layer
2890-5150 Outer core
5150-6378 Inner core

The crust varies considerably in thickness, it is thinner under the oceans, thicker under the continents. The inner core and crust are solid; the outer core and mantle layers are plastic or semi-fluid. The various layers are separated by discontinuities which are evident in seismic data; the best known of these is the Mohorovicic discontinuity between the crust and upper mantle.

Most of the mass of the Earth is in the mantle, most of the rest in the core; the part we inhabit is a tiny fraction of the whole (values below x10^24 kilograms):

atmosphere = 0.0000051
oceans = 0.0014
crust = 0.026
mantle = 4.043
outer core = 1.835
inner core = 0.09675

The core is probably composed mostly of iron (or nickel/iron) though it is possible that some lighter elements may be present, too. Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. We know most of this only from seismic techniques; samples from the upper mantle arrive at the surface as lava from volcanoes but the majority of the Earth is inaccessible. The crust is primarily quartz (silicon dioxide) and other silicates like feldspar. Taken as a whole, the Earth's chemical composition (by mass) is:
Earth-South America South America by Galileo

34.6% Iron
29.5% Oxygen
15.2% Silicon
12.7% Magnesium
2.4% Nickel
1.9% Sulfur
0.05% Titanium

The Earth is the densest major body in the solar system.

The other terrestrial planets probably have similar structures and compositions with some differences: the Moon has at most a small core; Mercury has an extra large core (relative to its diameter); the mantles of Mars and the Moon are much thicker; the Moon and Mercury may not have chemically distinct crusts; Earth may be the only one with distinct inner and outer cores. Note, however, that our knowledge of planetary interiors is mostly theoretical even for the Earth.

Unlike the other terrestrial planets, Earth's crust is divided into several separate solid plates which float around independently on top of the hot mantle below. The theory that describes this is known as plate tectonics. It is characterized by two major processes: spreading and subduction. Spreading occurs when two plates move away from each other and new crust is created by upwelling magma from below. Subduction occurs when two plates collide and the edge of one dives beneath the other and ends up being destroyed in the mantle. There is also transverse motion at some plate boundaries (i.e. the San Andreas Fault in California) and collisions between continental plates (i.e. India/Eurasia). There are (at present) eight major plates:

* North American Plate - North America, western North Atlantic and Greenland
Plate boundaries Earth's Plate Boundaries delineated by earthquake epicenters
* South American Plate - South America and western South Atlantic
* Antarctic Plate - Antarctica and the "Southern Ocean"
* Eurasian Plate - eastern North Atlantic, Europe and Asia except for India
* African Plate - Africa, eastern South Atlantic and western Indian Ocean
* Indian-Australian Plate - India, Australia, New Zealand and most of Indian Ocean
* Nazca Plate - eastern Pacific Ocean adjacent to South America
* Pacific Plate - most of the Pacific Ocean (and the southern coast of California!)

There are also twenty or more small plates such as the Arabian, Cocos, and Philippine Plates. Earthquakes are much more common at the plate boundaries. Plotting their locations makes it easy to see the plate boundaries.

The Earth's surface is very young. In the relatively short (by astronomical standards) period of 500,000,000 years or so erosion and tectonic processes destroy and recreate most of the Earth's surface and thereby eliminate almost all traces of earlier geologic surface history (such as impact craters). Thus the very early history of the Earth has mostly been erased. The Earth is 4.5 to 4.6 billion years old, but the oldest known rocks are about 4 billion years old and rocks older than 3 billion years are rare. The oldest fossils of living organisms are less than 3.9 billion years old. There is no record of the critical period when life was first getting started.

Strait of Gibraltar Space Shuttle view of the Strait of Gibraltar
71 Percent of the Earth's surface is covered with water. Earth is the only planet on which water can exist in liquid form on the surface (though there may be liquid ethane or methane on Titan's surface and liquid water beneath the surface of Europa). Liquid water is, of course, essential for life as we know it. The heat capacity of the oceans is also very important in keeping the Earth's temperature relatively stable. Liquid water is also responsible for most of the erosion and weathering of the Earth's continents, a process unique in the solar system today (though it may have occurred on Mars in the past).

Earth's atmosphere Earth's atmosphere seen at the limb
The Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water. There was probably a very much larger amount of carbon dioxide in the Earth's atmosphere when the Earth was first formed, but it has since been almost all incorporated into carbonate rocks and to a lesser extent dissolved into the oceans and consumed by living plants. Plate tectonics and biological processes now maintain a continual flow of carbon dioxide from the atmosphere to these various "sinks" and back again. The tiny amount of carbon dioxide resident in the atmosphere at any time is extremely important to the maintenance of the Earth's surface temperature via the greenhouse effect. The greenhouse effect raises the average surface temperature about 35 degrees C above what it would otherwise be (from a frigid -21 C to a comfortable +14 C); without it the oceans would freeze and life as we know it would be impossible. (Water vapor is also an important greenhouse gas.)

Earth from Apollo 11 View from Apollo 11
The presence of free oxygen is quite remarkable from a chemical point of view. Oxygen is a very reactive gas and under "normal" circumstances would quickly combine with other elements. The oxygen in Earth's atmosphere is produced and maintained by biological processes. Without life there would be no free oxygen.

The interaction of the Earth and the Moon slows the Earth's rotation by about 2 milliseconds per century. Current research indicates that about 900 million years ago there were 481 18-hour days in a year.

Earth has a modest magnetic field produced by electric currents in the outer core. The interaction of the solar wind, the Earth's magnetic field and the Earth's upper atmosphere causes the auroras (see the Interplanetary Medium). Irregularities in these factors cause the magnetic poles to move and even reverse relative to the surface; the geomagnetic north pole is currently located in northern Canada. (The "geomagnetic north pole" is the position on the Earth's surface directly above the south pole of the Earth's field; see this diagram.)

The Earth's magnetic field and its interaction with the solar wind also produce the Van Allen radiation belts, a pair of doughnut shaped rings of ionized gas (or plasma) trapped in orbit around the Earth. The outer belt stretches from 19,000 km in altitude to 41,000 km; the inner belt lies between 13,000 km and 7,600 km in altitude.
Earth's Satellite
Earth has only one natural satellite, the Moon. But

* thousands of small artificial satellites have also been placed in orbit around the Earth.
* Asteroids 3753 Cruithne and 2002 AA29 have complicated orbital relationships with the Earth; they're not really moons, the term "companion" is being used. It is somewhat similar to the situation with Saturn's moons Janus and Epimetheus.
* Lilith doesn't exist but it's an interesting story.

Distance Radius Mass
Satellite (000 km) (km) (kg)
--------- -------- ------ -------
Moon 384 1738 7.35e22
Offline Profile Quote Post Goto Top
 
Emory

Cheap drugs. kalamazoo maxalt blog contains notices on kalamazoo maxalt. this topic is focused on 24 hour pharmacy. avodart and hair loss page is relevant to avodart and hair loss. ephedrine hcl pricing site contains notices on ephedrine hcl pricing. this thread contains notices on purchase xanax no prescription. cialis is focused on side effects. cheap cialis is about cheap cialis. buy india is about buy india. appleton provigil page is about appleton provigil. information on flomax site is about information on flomax. alprazolam is relevant to alprazolam. cheyenne nexium site is devoted to cheyenne nexium.
Offline Profile Quote Post Goto Top
 
Emory

Online Pharmacy, Internet Pharmacy, Canadian Pharmacy - Pharmacy for you: concord periactin tells about concord periactin. hartford vincristine is about hartford vincristine. methadone abuse tells about methadone abuse. cheap prednisone is relevant to cheap prednisone. atorvastatin iowa contains notices on atorvastatin iowa. pharmacy association page is focused on pharmacy association. augmentin in dogs site is about augmentin in dogs. link contains notices on lorazepam. international pharmacy contains notices on international pharmacy program. topic contains information on pontiac retin a. xanax tablets is about xanax tablets. bulk discount contains notices on bulk discount. where to buy flexeril tells about where to buy flexeril. caffeine is relevant to caffeine. ketoconazole is about imidazoles.
Offline Profile Quote Post Goto Top
 
Emory

Some links for your attention: link contains information on buy zolpidem from uk. aldara is about aldara with insurance cost. elkhart metrogel contains notices on elkhart metrogel. concerta tells about everett concerta. brooks pharmacy tells about brooks pharmacy. aldara is relevant to medical treatment. abilify is devoted to get indian medicines. wholesale trade is about wholesale trade. pomona tenuate forum contains information on pomona tenuate.
Offline Profile Quote Post Goto Top
 
Emory

Pharmacy links: nizoral oral tells about nizoral oral. cheap pills is devoted to cheap pills. this topic is about abilify or geodon. cipro contains notices on cipro dog. this url contains information on somatropin cod. discount prescription is focused on discount prescription. klonipin is focused on klonipin. this site tells about phentermine no script. penicillins is relevant to penicillins. soma contains information on waukegan soma. chilliwack online pharmacy is about chilliwack online pharmacy. article contains information on bactroban cream 2. vibramycin is relevant to vibramycin. alameda clindamycin is focused on alameda clindamycin.
Offline Profile Quote Post Goto Top
 
Emory

Cheap Prescription Drugs. nystatin mouth wash page is relevant to nystatin mouth wash. this url is about sibutramine hcl. web site is focused on rockville finasteride. this link tells about mebendazole treatment. zithromax is relevant to zithromax. ritalin contains information on buy ritalin from canada. drugs mexico is about drugs mexico. monroe norvasc is focused on monroe norvasc. canadian pharmacies page is focused on canadian pharmacies. this link is about lawton testosterone.
Offline Profile Quote Post Goto Top
 
Emory

Canadian or International pharmacy has never been easier. anafranil sellers blog is relevant to anafranil sellers. order canada blog is about order canada. nsaia page contains notices on nsaia. fioricet is devoted to fioricet for headaches. colchicine dosage page tells about colchicine dosage. overseas pharmacy is about foreign pharmacy. t3 blog contains information on t3. inexpensive adipex site tells about inexpensive adipex.
Offline Profile Quote Post Goto Top
 
Emory

Lower Cost Pharmacy. care is devoted to care. reviews for fastin at gnc is focused on reviews for fastin at gnc. lowest price is devoted to lowest price. vaniqa on body is relevant to vaniqa on body. tamsulosin contains notices on sparks tamsulosin. paracetamol tells about paracetamol. mebendazole vs albendazole is about mebendazole vs albendazole. methadone contains notices on methadone health. drug prices is focused on drug prices. percocet is devoted to peabody percocet. nasal spray contains information on nasal spray.
Offline Profile Quote Post Goto Top
 
1 user reading this topic (1 Guest and 0 Anonymous)
ZetaBoards - Free Forum Hosting
Free Forums with no limits on posts or members.
« Previous Topic · Planets · Next Topic »
Add Reply