Presentation on theme: "Home Planet – the Earth Activity: The Earth as a model planet."— Presentation transcript:
Home Planet – the Earth Activity: The Earth as a model planet
Summary: In this Activity, we will investigate (a) Why astronomers study the Earth, and (b)The structure of the Earth.
(a) Why astronomers study the Earth... Look again on the slide of the Apollo view of the Earth rising over the Moon (title page), taken on the Apollo 8 mission on 22 Dec 1968.title page Apollo pictures like this one presented for the first time direct visual imagery of Earth as one celestial body among others in our Solar System, rather than as an all-encompassing “world”. * NASA Press releaseNASA Press release *
Now that space missions travel further than our Moon, we have even more graphic pictures of our Earth as a planet - here photographed with the Moon, at a distance of about 6 million kilometres, by the Galileo spacecraft on Dec 22 1992. * * NASA Press releaseNASA Press release
The Earth is a planet, and as such is studied by astronomers as well geologists. Modern astronomy and geology study “comparative planetology” - comparing planets with each other to find similarities, which in turn might suggest theories to explain their formation & evolution.
Astronomers study the Earth because it is the planet about which we know the most. Earth acts as a model planet with which to compare the properties of other planets. For example, if you study the other planets in the Solar System, you will notice that astronomers mostly quote vital statistics of other planets in terms of Earth. (For example, the mass of Mars is easier to conceptualize if we say that it is approx. 11% that of Earth, rather than that it has a mass of approx 642 400 000 000 000 000 000 000 kg!)
If you think that Earth is too familiar a topic to be of interest, wait till you see it from an astronomer’s point of view - it may surprise you!
(b) The structure of the Earth The Earth is affected by First we will investigate the Earth’s overall internal structure: astronomical influences from outside e.g. tidal forces between the Earth & Moon. biological influences on the surface e.g. production of oxygen by plants geological influences from within e.g. volcanic outflows
The density of rocks on the surface of the Earth is only approx. half this value - therefore at least some of the interior of the Earth must be very dense (otherwise the average density would not be so high). To determine the structure of the Earth, geologists study the way earthquake waves travel through its interior (“seismology”). The average density of the Earth can be estimated by measuring its gravitational attraction on satellites (including our natural satellite, the Moon). It turns out that the average density of the Earth is about 5.5 times the density of water.
The large-scale model seismologists have come up with for the Earth’s internal structure looks basically like this: crust mantle liquid outer core solid inner core
The inner core’s radius is approx. 20 % of that of the whole Earth, with a density of approx. 4.6 times that of the Earth’s crust. The inner core is hot (temperatures up to nearly 5000 C), metallic, and rotates very slightly faster than the rest of the Earth. solid inner core
The outer core extends out to almost one-third of the Earth’s radius, with density gradually decreasing until it drops at its outer surface to approx. 1.6 times that of the Earth’s crust. liquid outer core Seismological evidence suggests that the outer core is hot, liquid and metallic, but its exact composition is not known for certain.
Made up of solid silicate minerals, its density gradually decreases until it drops at its outer surface to only slightly more than that of the Earth’s crust. mantle The mantle extends out almost to the surface of the Earth. Though cooler than the core, (temperatures from approx. 2 200 C down to 1 200 C), the mantle is still hot enough to undergo plastic flow - that is, move in convective currents like those in water heated on a stove.
By comparison, the crust of the Earth is only approx. 35 km thick under the continents (and approx. 5 km thick under the oceans), but together with the atmosphere it supports all the Earth’s known lifeforms, including us. crust
The convective currents in the Earth’s mantle are driven by the considerable temperature difference between the hot core (approaching 5000 C) and the relatively cool crust. The molten rock in the mantle is called magma. The convective currents in the mantle drag along regions of the (thin) crust. The Earth’s crust is made up of a number of separate continental & oceanic plates, all floating on the mantle.
The crust is thinnest under the oceans, where it tends to be made up of heavy, plastic oceanic basalt (solidified lava). ocean crust mantle Where the convection currents under the oceans sink down, they drag down regions of crust, forming deep chasms called midocean trenches.
Where convection currents “well up” under the ocean, magma (molten rock) from the mantle lifts up the crust to form “oceanic ridges”, such as the mid-Atlantic ridge. This upwelling of lava pushes the oceanic plates apart, causing “continental drift” - at a few centimetres per year.
When continental plates collide, they produce “folded mountain chains”. The Himalayan Mountains show intricate folding patterns resulting from the collision of the Indian & Asian continental plates.
When a continental plate collides with an oceanic plate, oceanic basalt continental granite mantle the heavy plastic oceanic basalt tends to slide under the light, brittle continental granite. The rising crust crumples up into coastal mountain ranges.
In the process, the basalt is likely to heat up & melt, forming outflows called lava & volcanic activity - volcanism - and associated earthquakes. The Andes mountains in South America are the result of the Pacific Ocean floor slipping under the continental plate.
This NASA globe shows the boundaries between some of Earth’s tectonic plates, with associated volcano & earthquake regions. Andes mountains
Image Credits NASA Photo AS08-14-2392: High-oblique view of Moon’s surface showing earth rising above horizon http://images.jsc.nasa.gov/images/pao/AS8/10074963.jpg NASA Photo NUMBER p-41508c: Image of the Earth and Moon from Galileo http://nssdc.gsfc.nasa.gov/image/planetary/earth/gal_earth_moon.jpg NASA: View of Australia http://nssdc.gsfc.nasa.gov/image/planetary/earth/gal_australia.jpg NASA: Volcanoes & Earthquakes http://www.earth.nasa.gov/gallery/Originals/Volcanes&Quakes.jpg NASA: The Western Himalayas (from the Shuttle Atlantis) http://kidsat.jpl.nasa.gov/kidsat/exploration/explorations/ESC.00212656/index. html
Hit the Esc key (escape) to return to the Index Page
Press Releases: NASA Photo AS08-14-2392: High-oblique view of Moon’s surface showing earth rising above horizon http://images.jsc.nasa.gov/images/pao/AS8/10074962.htm File Name: 10074962.jpg Film Type: 70mm Date Taken: 12/22/68 Description: High-oblique view of the moon's surface showing the earth rising above the lunar horizon, looking west-southwest, as photographed from the Apollo 8 spacecraft as it orbited the moon. The center of the picture is located at about 105 degrees east longitude and 13 degrees south latitude. The lunar surface probably has less pronounced color than indicated by this print. Click here to return to the Activity!
Press Releases: NASA Photo p-41508c: Image of the Earth and Moon from Galileo http://nssdc.gsfc.nasa.gov/image/planetary/earth/gal_earth_moon.jpg GALILEO December 22, 1992 P-41508 Eight days after its encounter with the Earth, the Galileo spacecraft was able to look back and capture this remarkable view of the Moon in orbit about the Earth, taken from a distance of about 6.2 million kilometers (3.9 million miles), on December 16. The picture was constructed from images taken through the violet, red, and 1.0-micron infrared filters. The Moon is in the foreground, moving from left to right. The brightly-colored Earth contrasts strongly with the Moon, which reflects only about one-third as much sunlight as Earth. Contrast and color have been computer-enhanced for both objects to improve visibility. Antarctica is visible through clouds (bottom). The Moon's far side is seen; the shadowy indentation in the dawn terminator is the south-Pole/Aitken Basin, one of the largest and oldest lunar impact features, extensively studied from
Galileo during the first Earth flyby in December 1990. The Galileo project, whose primary mission is the exploration of the Jupiter system in 1995-97, is managed for NASA's Office of Space Science and Applications by the Jet Propulsion Laboratory. Click here to return to the Activity!