1 letter:
.

2 letters:
ar, au, ba, ca, ce, dy, er, eu, gd, ge, ho, ki, la, lu, nd, pm, pr, sc, si, sm, tb, tm, tt, xe, yb

3 letters:
air, bed, bel, day, dig, ert, geb, gps, keb, man, map, mud, rut, sap, sky, tdt, trm

4 letters:
asia, bank, bury, clay, core, dirt, dust, frey, gaea, gaia, hill, land, mine, moon, noaa, owlt, pica, plow, pole, rank, rock, rtlt, sial, sima, soil, star, turn, vent, void, year, ymir, zone

5 letters:
alien, aloft, argon, aruru, break, brown, calif, chasm, crust, dagan, dagon, delve, ditch, dwarf, enuki, ether, fault, freyr, genie, globe, gnome, hogan, horst, jinni, kalif, magma, mined, mitra, mound, nammu, orbit, parch, peter, phase, plate, polar, quake, seism, shift, shock, slide, spade, squat, stone, titan, trove, truea, umber, water, world, xenon

6 letters:
altair, apogee, aurora, barium, barrow, boring, bowels, bunker, caliph, cerium, cradle, direct, djinni, djinny, dugout, erbium, global, ground, hadean, height, hotbed, humans, hutton, jinnee, kaliph, khalif, manned, mantle, massif, meteor, mining, nugget, oxygen, pangea, parsec, plough, pluton, primal, region, rocker, secpar, sienna, silica, sluice, stream, syzygy, tellus, trench, trough, unfirm, uplift, uplink, worlda

7 letters:
anthill, archean, backhoe, balloon, calcium, canopus, compass, damkina, dig out, earthen, earthly, equator, equinox, erosion, fictile, geodesy, geology, gravity, holmium, horizon, ice age, isogone, landing, land up, mankind, massive, moraine, mundane, oceanus, orbiter, orogeny, pangaea, perigee, plastic, polaris, precess, profile, revolve, seismal, seismic, shamash, silicon, skyline, sputnik, tar pit, temblor, terbium, terrene, thulium, tropics, tumulus, volcano, yttrium

8 letters:
airspace, altitude, anunnaki, arcturus, barbette, brownish, cislunar, cut into, dateline, denebola, downfall, drilling, dry land, earthing, earthman, earth up, ecliptic, endogeny, eruptive, europium, fracture, geomancy, geophagy, humanity, inferior, interior, kennelly, khalifah, latitude, lutecium, lutetium, magnetic, mephitis, meridian, moldable, molehill, monazite, mosander, on earth, parallel, phaethon, philemon, plutonic, polestar, priscoan, samarium, scandium, scorched, separate, sky wave, stratify, sublunar, superior, tectonic, temporal, titaness, twilight, volcanic, westerly, wormcast, ygdrasil

9 letters:
abundance, air space, antipodal, antipodes, batholite, batholith, biosphere, bountiful, cataclysm, cavendish, collector, continent, date line, earthborn, earthlike, earthling, ellipsoid, endogenic, epicenter, epicentre, extrusive, footprint, formation, formicary, gas giant, geography, geophagia, geosphere, grounding, hagridden, heaviside, humankind, hydrology, inhabited, inversion, irruptive, lanthanum, lightning, longitude, meteorite, meteoroid, neodymium, planetary, pole star, ptolemaic, satellite, solar day, st. peter, sublunary, surficial, tectonics, tellurian, tube well, turn over, van allen, variation, whirlwind, worldwide, yggdrasil, ytterbium

10 letters:
angledozer, antipodean, archeozoic, armageddon, atmosphere, bastnasite, bhumi devi, borrow pit, civil time, copernican, dark-brown, despicable, dysprosium, earthbound, earthquake, embankment, empedocles, excavation, fault line, gadolinium, geocentric, geophysics, geothermal, geothermic, glaciation, gravimeter, hadean eon, human race, ionosphere, local time, millennium, north pole, north star, plumb line, polar star, polar zone, promethium, retrograde, revolution, sheet pile, solar year, south pole, structural, superlunar, translunar

11 letters:
agonic line, anamorphism, archaeozoic, archean eon, bastnaesite, catastrophe, cosmography, damgalnunna, direct tide, discernible, driven well, endogenetic, fossilology, fossil fuel, frigid zone, geographics, geophilidae, grave mound, gravitation, ground wave, hadean aeon, hadean time, hydrography, hydrosphere, hypsography, leap second, lithosphere, mellowingly, meteorology, micrometeor, misch metal, outer space, parashurama, rift valley, saint peter, sheath pile, simon peter, spacefaring, spaceflight, space probe, strip-mined, superlunary, terra firma, terrestrial, torrid zone, translunary, underground, untouchable, watercourse

12 letters:
archean aeon, burial mound, diastrophism, earthshaking, earth mother, eratosthenes, geochemistry, geophysicist, geothermally, human beings, james hutton, katamorphism, last quarter, lunar crater, paleogeology, paleontology, physiography, praseodymium, priscoan eon, quintessence, satellite tv, semidiameter, sheet piling, sidereal day, solar energy, solid ground, space travel, subterranean, undiscovered

13 letters:
body of water, constellation, crustal plate, down-to-earth, earth's crust, earth science, first quarter, gastromycetes, geologic time, geostationary, glacial epoch, gravity meter, hypervelocity, isogonal line, isogonic line, jovian planet, lunar eclipse, magnetic pole, meteorologist, meteor shower, meteor stream, palaeogeology, palaeontology, perpendicular, plutonic rock, precipitation, priscoan aeon, scintillation, shooting star, sidereal year, silicon oxide, space shuttle, standard time, subterraneous, tropical year, tropical zone, volcanic rock

14 letters:
a. e. kennelly, archeozoic eon, celestial pole, command module, coriolis force, ephemeris time, gasteromycetes, geosynchronous, glacial period, global warming, magnetic storm, mean solar day, micrometeorite, micrometeoroid, nuclear winter, oil production, retaining wall, solar constant, solar parallax, temperate zone, treasure trove, van allen belt

15 letters:
annual parallax, apollo asteroid, atomic number 8, coriolis effect, earth's surface, geographic area, geological time, henry cavendish, inferior planet, magnetic needle, mercury program, plate tectonics, silicon dioxide, superior planet, visible horizon

16 letters:
anomalistic year, apparent horizon, archaeozoic aeon, atomic number 14, atomic number 18, atomic number 20, atomic number 21, atomic number 39, atomic number 54, atomic number 56, atomic number 57, atomic number 58, atomic number 59, atomic number 60, atomic number 61, atomic number 62, atomic number 63, atomic number 64, atomic number 65, atomic number 66, atomic number 67, atomic number 68, atomic number 69, atomic number 70, atomic number 71, circumnavigation, conic projection, crustal movement, diurnal parallax, equinoctial year, extraterrestrial, geographic point, geological fault, gravity gradient, line of latitude, oliver heaviside, ptolemaic system, sensible horizon, terrestrial time

17 letters:
astronomical unit, astronomical year, celestial horizon, copernican system, foucault pendulum, geographical area, geographical zone, geographic region, geothermal energy, greenhouse effect, lanthanide series, line of longitude, magnetic meridian, sanitary landfill, tectonic movement, transmission time, twenty-four hours, weather satellite

18 letters:
absolute magnitude, conical projection, family geophilidae, geographical point, one-way light time, physical geography, terrestrial planet

19 letters:
class gastromycetes, earth-received time, geocentric parallax, geographical region, geophysical science, geostationary orbit, gravitational force, mercator projection, prevailing westerly, seismic disturbance

20 letters:
artificial satellite, astatic galvanometer, class gasteromycetes, geological formation, geosynchronous orbit, inferior conjunction, parallel of latitude, satellite television, superior conjunction, terrestrial guidance

21 letters:
arthur edwin kennelly, carl gustaf mossander, estraterrestrial body, geological phenomenon, heliocentric parallax, mercator's projection, plate tectonic theory, round-trip light time, st. peter the apostle

22 letters:
biogeographical region, extraterrestrial being, james alfred van allen

23 letters:
extraterrestrial object, international date line, saint peter the apostle

24 letters:
communications satellite, gravitational attraction, meteorological satellite

25 letters:
global positioning system

26 letters:
terrestrial dynamical time

27 letters:
michelson-morley experiment, precession of the equinoxes

40 letters:
national oceanic and atmospheric administration