menarik apa memang proses tektonik lempeng hanya ada di bumi ?
On 10/11/07, Fajar Lubis <[EMAIL PROTECTED]> wrote: > > Sampai tahun 60-an para ahli masih memperdebatkan apakah air tawar berasal > dari dalam bumi (mata air, air hasil dari pembentukan batuan dsb) ataukah > dari hujan. > > Pada dasawarsa 70-an hampir semua ahli sumberdaya air sepakat bahwa 90% > air tawar berasal dari siklus hujan (siklus hidrologi). Ini yang menerangkan > kenapa hampir semua model ketersediaan air dihitung dengan konsep > berdasarkan ketersediaan air hujan di wilayah tersebut. > > 10 % yang bukan berasal dari hujan dikalsifikasikan sebagai air juvenil > (berasal dari inti bumi), air metamorfik (berasal dari proses pembentukan > batuan metamorf), air magmatik, air fosil dll. Mengingat komposisi kimianya > yang kaya dengan mineral, maka sulit untuk dikatakan sebagai sumber air > tawar yang layak dikonsumsi secara langsung. > > Sepakat dengan Pak Awang ... Memang perkembangan dalam ilmu penentuan umur > secara umum membawa para ahli kepada kesimpulan bahwa air berasal dari > `extra terestial` yang dibawa oleh meteor dan komet 3,8 milyard tahun yang > lalu. > > Pertanyaan yang menarik adalah fenomena tabrakan meteor/komet/planetisimal > ini tentu saja akan berlangsung di planet-planet yang lain. Lalu mengapa > hanya di Bumi fenomena ini dapat berkondensasi menjadi lautan yang akhirnya > memicu terjadinya siklus hidrologi? > > Salahsatu jawaban yang ada saat ini adalah akibat proses tektonik bumi > yang memicu letusan gunungapi yang pada akhirnya membentuk lapisan atmosfer. > Tentu saja masih banyak jawaban lain yang menunggu pembuktian dari para ahli > kebumian. > > Apapun jawaban yang benar ... Tampaknya alam Bumi ini adalah satu kesatuan > yang saling kait mengkait.... > > > Keep on search .... Selamat Iedul Fithri 1428 H Mohon Maaf Lahir Batin, > Fajar (1141) > > ============================================== > Hystory of Water Cycle (from many sources) : > > • Water was delivered to primitive Earth by planetesimals, meteors and > comets during its accretionary phase, which was largely complete by > 3.8billion years ago (bya). > > • Water was released from Earth's crust in volcanic eruptions (degassing), > but remained in the atmosphere as long as Earth's surface temperature was > >100°C. > > • Once Earth cooled below 100°C, most water condensed to form the oceans. > > • Enough water vapor and CO2 remained in the atmpsohere to keep the > temperature of Earth's surface above freezing; without this Greenhouse > effect the Earth might have remained frozen, like Mars. > > • There is good evidence of liquid water on Earth at 3.8 bya, and the > volume of water has not changed appreciably since then. > > • Throughout Earth's history, changes in relative sea level have occurred > during times of tectonic activity that increases (or decreases) the volume > of submarine mountains, and/or global temperature changes that lead to > glaciation/deglaciation. > > • The geologic record shows large changes in ocean volume, as evidenced by > del-18O of marine carbonates, that accompanied repeated glaciation during > the Pleistocene Epoch (2 mya). > > • During the last peak glaciation (18,000 ybp) 42,000,000 km3 of seawater > was trapped in polar ice caps, or 3% of oceans volume, and this lowered > sealevel by 120 m relative to the present day. > > • Continental glaciations thus represent a major disruption in the Earth's > hydrologic cycle, or a loss of steady state conditions. > > • Some examples of perturbations in the hydrologic cycle due to glacial / > interglacials and the accompanying global cooling include: > - lower rates of evaporation > - reduced circulation of moisture through the atmosphere > - reduced precipitation > > • One model suggests that 18,000 ybp total ppt was 14% lower than at > present, deserts expanded, NPP and terrestrial biomass were lower, greater > erosion increased dust flux to the deep sea as recorded in deep sea > sediments and ice caps, and loess deposits on land. In contrast, the SW US > climate ameliorated during this time period. > > ....... > > > --------------------------------- > Moody friends. Drama queens. Your life? Nope! - their life, your story. > Play Sims Stories at Yahoo! Games.
