Earth Definition and 75 Discussions

Earth is the third planet from the Sun and the only astronomical object known to harbor and support life. About 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is covered with water, mostly by oceans, seas, gulfs, and other salt-water bodies, but also by lakes, rivers, and other freshwater, which together constitute the hydrosphere. Much of Earth's polar regions are covered in ice. Earth's outer layer is divided into several rigid tectonic plates that migrate across the surface over many millions of years, while its interior remains active with a solid iron inner core, a liquid outer core that generates Earth's magnetic field, and a convective mantle that drives plate tectonics.
Earth's atmosphere consists mostly of nitrogen and oxygen. More solar energy is received by tropical regions than polar regions and is redistributed by atmospheric and ocean circulation. Greenhouse gases also play an important role in regulating the surface temperature. A region's climate is not only determined by latitude, but also by elevation and proximity to moderating oceans, among other factors. Severe weather, such as tropical cyclones, thunderstorms, and heatwaves, occurs in most areas and greatly impacts life.
Earth's gravity interacts with other objects in space, especially the Moon, which is Earth's only natural satellite. Earth orbits around the Sun in about 365.25 days. Earth's axis of rotation is tilted with respect to its orbital plane, producing seasons on Earth. The gravitational interaction between Earth and the Moon causes tides, stabilizes Earth's orientation on its axis, and gradually slows its rotation. Earth is the densest planet in the Solar System and the largest and most massive of the four rocky planets.
According to radiometric dating estimation and other evidence, Earth formed over 4.5 billion years ago. Within the first billion years of Earth's history, life appeared in the oceans and began to affect Earth's atmosphere and surface, leading to the proliferation of anaerobic and, later, aerobic organisms. Some geological evidence indicates that life may have arisen as early as 4.1 billion years ago. Since then, the combination of Earth's distance from the Sun, physical properties, and geological history have allowed life to evolve and thrive. In the history of life on Earth, biodiversity has gone through long periods of expansion, occasionally punctuated by mass extinctions. Over 99% of all species that ever lived on Earth are extinct. Almost 8 billion humans live on Earth and depend on its biosphere and natural resources for their survival. Humans increasingly impact Earth's surface, hydrology, atmospheric processes, and other life.

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  1. E

    How to calculate Earth speed of the Moon induced orbit?

    It didn't work and I don't know how to do it.
  2. DANIELWR1998

    How do I find way of comparing the density of the Earth and the Moon?

    Surface acceleration is proportional to density and radius of planet (as 2 powers of R cancel with the volume) g(moon)/g(earth) = density(moon)*radius(moon)/density (earth)*radius(earth) = (1/4)*density(moon)/density(earth)
  3. Remixex

    Triangles inside a circle to represent raypaths inside an ideal Earth

    I have managed to get some of the required distances and angles. I have the distance ##a##, the velocity inside the mantle, the total radius of the Earth ##R_t## as well as mantle and core radii. I have also figured out the angle of incidence, however I cannot get the refracted angle with the...
  4. Lren Zvsm

    Sapient Life Indigenous to a Planet Orbiting a Red Dwarf

    I am considering writing a story that features aliens indigenous to a planet orbiting a red dwarf star. Even so, because of its proximity to the red dwarf, the planet's surface receives much more radiation than Earth's surface does. What is more, the planet has no moon to stabilize its...
  5. H

    I Image for increase in gravitational potential energy in radial field

    A question to physicists: What sort of real world scenario / image would *best* depict the increase in gravitational potential energy in a radial field? Would a rocket traveling through the Earth's atmosphere suffice or are there better alternatives? This image would have to be relevant to the...
  6. RemotePhysics

    Require help with angular velocity and people flying off the planet!

    My solutions (attempts) : a> w=v/r | r=6.35x10^6m | therefore V=7.04x10^-5 m/s b> speed of rotation is faster at the equator than the pole as w=v/r. As w remains constant, as r increases towards the pole V has to decrease. c> F = W - R d> Stuck here. I presume that I have to use the equation...
  7. O

    I How does Jupiter protect the Earth from collision with space rocks?

    I read (in "The View From The Center") that Jupiter protects the Earth from collision with large space rocks, asteroids, etc. What I can't get out of my mind is that could it also cause collisions. A large rock (initially not heading for Earth) could be put on a different path by Jupiter's...
  8. W

    Electrons @ battery negative terminal

    Does the negative terminal of a battery have a negative charge due to having a surplus of electrons? If so, then why do the surplus electrons from the negative terminal of the battery not discharge to the human body or Earth (which have a neutral charge) when touched?...thereby causing the...
  9. P

    What is the maximum depth to which a P-wave ray can travel?

    I've created an excel spreadsheet with the given model in addition to calculating radius of the layer by subtracting depth from 6371. I've calculated Zf. I've also found what I think is vs by doing alpha * (radius column/6371), but that could be wrong. I know I need to find where 20/6371 =...
  10. matai

    Using Integrals to Calculate the Rotational Energy of Earth

    So I found the linear velocity by using the circumference of the Earth which I found to be 2pi(637800= 40014155.89meters. Then the time of one full rotation was 1436.97 minutes, which I then converted to 86164.2 seconds. giving me the linear velocity to be 465.0905584 meters/second. I know that...
  11. Mlesnita Daniel

    B Ideas to protect the Earth from possible asteroid impacts

    Do you have any own idea, on a way to protect the Earth from a possible asteroid impact? (You can not use technologies that are not invented yet, or imaginary. Those that can be invented in the next, let's say, 10 years, are allowed)
  12. Delta2

    B Water colour in Mars

    I guess water in Earth , in big lakes or seas, looks blue because the Earth's sky is blue and the water's surface reflects the sky. Now if there would be some big lake of water at Mars, how the water surface colour would be? I guess the colour of Mar's sky which is red (right or wrong?) It is...
  13. P

    What was the rotational velocity of Earth on Dec 31, 1899

    I ask because time is defined with reference to this day (the SI second is based on a caesium clock is calibrated with reference to the 1952 ephemeris time standard, which was based on a second being 1/86 400th of Jan 0, 1900 (with Jan 0 being Dec 31 of 1899). So... how do I calculate the...
  14. P

    I How many degrees / radians is one full orbit of the Earth?

    One day consists of slightly more than 360° of rotation (360.9856°) on it's axis (due to Earth's orbit around the Sun). I imagine that one orbit is also either > or < 360° around the sun, relative to the motion of the sun around some object. Is this true, or is the orbit of the Earth...
  15. E

    Finding the change in weight from the force & difference in height (y)

    Information Given:In 1956, Frank Lloyd Wright proposed the construction of a mile-high building in Chicago. Suppose the building had been constructed. Question: Ignoring Earth's rotation, find the change in your weight if you were to ride an elevator from the street level, where you weigh 708...
  16. Craftek_Ana

    B Traveling to Mars and time dilation

    If/when we go to Mars how will we deal with time dilation due to the gravitational differences between the two planets?
  17. W

    B Light spectrum of planet Earth as seen from space

    Has the spectrum of light that is reflected off planet Earth ever been measured from outer space? (In the same sense that we measure spectra of the light emitted/reflected from other celestial bodies in astronomy). If so, would it be possible that there could be dips in the spectrum resulting...
  18. riveay

    Simulating Jules Verne Earth to the Moon trip?

    Has anybody attempted simulating the trip to the moon described by Jules Verne? I've done a bit of research and found this two posts:
  19. A

    Satellites and the Earth's Magnetic Field

    So i was just wondering if a satellite's circuitry could be affected by the Earth's own magnetic field inducing a current, if it was moving through it quickly enough (the space station for example), and how it might mess with it? Also considering a satellite is a big hunk of metal, could passing...
  20. doglover9754

    What in gravity makes water on Earth into a ball?

    So, from my last thread “Why doesn’t the water fall out of the Earth?” I asked if the reason why water doesn’t fall out of the Earth even on its tilted axis. Then the conclusion was gravity. To be more precise, gravity is the one that pulled the water on Earth into a ball form. What in gravity...
  21. BTA

    Why would aliens come here? (resurrected)

    I asked myself this question today, found that exact question asked here (February 10, 2005)... and I could not say anything, not even a squeak. Well, boil that dustmote! "Why would aliens come here?" I ask and the voices in my head speak. We are far from the galactic center of an average...
  22. mr1batman

    B Distance between the Earth and The Moon

    we know that the moon is far away the distance between us and the moon can fit all the other 7 planets and some small dwarf planets but how ? it would take us 3 days to reach the moon and the spacecraft were traveling in at least 240,000 miles it should take us more than a year to reach the...
  23. D

    Why doesn’t the water fall out of the Earth?

    So I was on my way to school this morning and looking at the beach made me think of something. Why doesn’t the water on Earth fall out and into space? Like, if you really didn’t think too hard, you’d be like, yeah, the Earth is tilted, so why, doesn’t the water fall out like a glass of water? If...
  24. xaratustra

    Foucault pendulum and a round globe

    Imagine we are all cavemen without satellite technology and just discovered the Foucault pendulum! As we know the angle of presession depends on the latitude. This can be used to prove that the Earth is rotating, right? Now by putting several Foucault pendula around the Earth, at equidistant...
  25. K

    Error analysis E/M experiment -- help please

    So I am doing the charge to mass experiment and determining the relationship between: 1. accelerating voltage and radius formed by the electron beam 2. magnetic field strength and radius formed by electron beam Theoretically I should obtain an equation of the form: r = (1/B) *sqrt(2mV/e) where...
  26. C

    Why don't we feel the Earth's rotation?

    Pardon me if this seems like an incredibly naive question. Perhaps the question could also be rephrased as such: "Why do the laws of classical mechanics hold true with Earth as a frame of reference?" A quick google search turned up the usual answer: the Earth rotates at a constant speed...
  27. hamischism

    B Star trails and the Earth's movemement

    Greetings, I wonder if someone could please kindly give a physics explanation for the phenomenon of circular star trails when Earth is moving 67 times faster laterally than it is rotating? Thanks very much in advance...
  28. E

    Uranium-Lead Dating

    I just recently read about how we got to know the true age of the Earth but I am a bit confused and curious about one thing. The mineral or rock is initially going to be a uranium right? If it is, isn't all of it going to decay at the same rate? I know that a radioactive reaction is spontaneous...
  29. A

    How can the neutral outer core generate a magnetic field?

    Even if the outer core is convecting and conductive it is still charge neutral, so how can a Magnetic field be generated? Maxwells Equation say there needs to be net charge moving for a Magnetic field to be generated.
  30. Solomei

    Earth's search for stability

    Im quite fascinated over how Earth is constantly trying to stabilise itself. What is your most interesting observation or 'happening' about climate change?
  31. G

    Does current flow back to the power plant through the ground?

    Hi. I fear I might not have understood some fundamental concepts about electric power transmission. So we have "neutral" which is brought to Earth potential. Does this mean the electrical circuit from the power plant over highly conductive aluminium cables to my home closes back to the power...
  32. Tone L

    Convert Longitude/Latitude dependent upon the location on the Earth

    I am planning to plot all the observations made by a satellite in two respective grid boxes. One grid located at the equator and one grid located at the mid latitudes... Each grid box will be a 10° x 10° box. However, due to the shape of the Earth the area of each box will indeed not be the...
  33. V

    I Why exactly does the ocean bulge on both sides of the Earth?

    Here's what my prof says: "Define F_{mean} to be the mean force, F_close to be the force on the side of the Earth closer to the moon, and F_far to be the force on the side of the Earth furthest away from the moon. On the closer side the net force is F_close - F_mean > 0 On the further side the...
  34. X

    Inelastic Collision

    Homework Statement A student runs an experiment with two carts on a low-friction track. As measured in the Earth reference frame, cart 1 (m = 0.48 kg ) moves from left to right at 1.0 m/s as the student walks along next to it at the same velocity. Let the +x direction be to the right. A. What...
  35. E

    I How does mars have a magnetic field, with a cooled core?

    I have been studying astronomy and astrophysics for about 2 years now, though on my own time and by my self. A recent question came into my mind, Can arctic planets exist close to their star? Now, in my understanding of planetary science, in order for a planet to be cool and close to the sun, it...
  36. Tom MS

    B Does the Coriolis Effect Occur When Wind Moves Horizontally?

    I'm trying to get an understanding of the Coriolis effect, and I understand it when the wind moves longitudinally (North-South). Basically, the wind has a certain horizontal component of its velocity due to the rotation of the Earth, and as it moves North or South the rotation of the Earth...
  37. A

    B Determining the greater force?

    Q: Fred is on Earth, and Jane is on the Moon. a) Each lifts a 2.0 kg rock. Who has to apply the larger force? b) Each throws the rock horizontally with initial speed of 6.0 metres per second. Who applies the larger force? For both questions, I wrote: Fred, because the gravity on Earth is...
  38. S

    Coriolis effect causes in motion of a free falling object

    I don't understand what are the causes of the Coriolis effect for objects moving with respect to Earth. For istance consider an object free falling on the Earth from an height h. Its tangential velocity its greater than the velocity of an object on the surface of Earth, hence it moves eastward...
  39. J

    Bose Condensation in 2D

    Hi, I was given the following question: Show that Bose condensation does not occur in 2D. Hint: The integral you will get when you write the formula for N is doable in elementary functions. You should find that that N ∝ ln(1 − e βµ). I do indeed find that N ∝ ln(1/(1 − e βµ)) ∝ ln(1 − e βµ)...
  40. C

    Energy from cosmic microwave background

    Hello everyone I've a question about the cosmic microwave background which my nephew asked me a couple of days ago. How much energy hits the Earth each year from the CMB? I'm assuming here that it is measurable in this way, but apologies if not. Thanks in advance for your help. Chris
  41. W

    How far would a planet be from the Earth, when its....

    Homework Statement How far would be a planet from the earth, when its period would be 2 years? T = 2 years/730 days a = 150*106km Homework Equations a3/T2 = C (C is the Kepler-Constant) The Attempt at a Solution I tried inserting T in days and years, but I always get a wrong solution, since C...
  42. F

    Escape Velocity = Freefall from Height of One Radius?

    I was doing some calculations using the escape velocities from Earth, Moon and Mars. Then by chance I calculated the velocities attained when an object was "dropped" from a height of the radius on each of these bodies, assuming the acceleration due to gravity remained constant during the fall...
  43. M

    How often do satellites pass the moon?

    So, I have really no background in astrophysics (other than touching on some areas in general physics and calculus). I understand that asking questions such as the one in my title, that I would need to be more specific, and I will attempt to be as specific as I can. I understand that most...
  44. Stephanus

    Orbits in the universe

    Dear PF Forum, Lunar Satelite orbits the moon, The moon orbits the earth, The Earth orbits the sun, I know that some of you know about this picture You might want to tell me. "No Steven, the Sun also orbits the earth" But for all practical purpose, we'd say that the earth orbits the sun. So...
  45. S

    Simulating exploding planets

    I know planets are very stable and don't explode, but here's something I would love a physicist to run on a powerful computer, maybe using some FEM model. Let's say we will the inner core of planet Earth with TNT, say a sphere with radius 2000 km and ignite it. What would the explosion look like...
  46. O

    Refraction as an explanation for light curvature

    Wikipedia states that: "If the measurement is close enough to the surface, light rays can curve downward at a rate equal to the mean curvature of the Earth's surface. In this case, the two effects of assumed curvature and refraction could cancel each other out and the Earth will appear flat in...
  47. A

    Watching Earth travel in space....what should be the location

    Dear All, Is it possible to watch Earth orbiting the sun in space like we watch a car coming towards us on a highway ? I mean, I would like to see it coming towards my spaceship at the rate of say 50 km/hr. Now some questions - 1. What should be my location and speed of my spacecraft...
  48. LeoPedranjo

    Gravitational field

    Hey guys, take a look at this question if you may Suppose the moon, instead of a sphere, is a disc orbitating the Earth ( the moon's total mass is equal to the disc's total mass), the intern radius of the disc is equal to half the distnce between moon and Earth's center of mass and the external...
  49. J

    Earth's Gravity

    Hey guys! What would be the gravitational effect of Earth on it's surface, if somehow the density of mass was uniform and equal to 2/5 of the real value? Assuming that the size e shape os the planet doesn't change.
  50. LeoPedranjo

    Gravitational Field

    Hi guys! What would happen to objects on the Earth's surface if it SLOWLY stopped spinning and Earth's gravitational field was kept as always. Thx