Rodinia

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Peta dari Rodinia

Rodinia adalah superbenua tertua yang jejak geologinya masih bisa dilacak oleh para ahli geologi. Superkontinen ini jauh lebih tua daripada Pangea, tetapi masih lebih muda daripada superbenua Columbia (1800-1500 juta tahun) dan Vaalbara (3600 juta tahun). Walaupun lebih muda, Rodinia dipercayai bukan hanya sebuah hipotesis lagi, tetapi betul-betul pernah ada.

Nama Rodinia sendiri dipopulerkan oleh Dalziel (1991), Moores (1991) dan Hoffman (1991). Rodinia adalah kata dalam bahasa Rusia yang berarti “motherland” (tanah ibu/leluhur). Konon, Rodinia mulai terbentuk sekitar 1400 juta tahun yang lalu (Ma), pada saat 3 sampai 4 benua mulai menyatu. Konon lagi, pada sekitar 1000 Ma Rodinia ini sudah jelas terkonsolidasi, yang ditunjukkan oleh pembentukan sebuah rangkaian pegunungan. Para ahli menyebut proses pembentukan rangkaian pegunungan itu dengan nama Grenville Orogeny.

Istilah Grenville Orogeny diambil dari sebuah komplek batuan metamorf terdeformasi yang ditemukan di kota Grenville, Quebec, Canada. Grenville Province, demikian nama geologi komplek batuan metamorf itu, tersebar memanjang sampai ke wilayah Texas sekarang. Batuan Grenville Province didominasi oleh Gneiss dan dipercaya juga berada di Brazil bagian barat, menjadi bagian dari kraton Amazonia (Tohver et al., 2002), tapi diberi nama lain oleh para ahli geologi, Formasi Nova Floresta.

Lifetime

Geologic evidence suggests that Rodinia terbentuk and broke apart in the Neoproterozoic, probably existing as a single continent from 1 billion years ago until it began to rift into eight smaller continents about 800 juta tahun yang lalu. It is thought to have been largely responsible for the cold climate of the Neoproterozoic era.

Rodinia is thought to have been preceeded by the Vaalbara supercontinent and succeeded by the Pangaea supercontinent, with intervening periods when several continents existed.

Formasi

Rodinia terbentuk sekitar 1.3 miliar tahun lalu dari tiga atau empat benua, an event known as the Grenville orogeny. The absence of fossils of hard-shelled organisms and reliable paleomagnetic data make the movements of continents earlier in the Precambrian, prior to this event, uncertain. (See Columbia (supercontinent) for one possible reconstruction of an earlier supercontinent.)

The arrangement of Rodinia has been hypothesized using paleomagnetic data from the Seychelles islands and India and the Grenville mountain belts, which were formed by the Grenville orogeny and span multiple modern continents, as references.

Although the details are disputed by paleogeographers, the continental cratons that formed Rodinia appear to have clustered around Laurentia (proto-North America), which constituted Rodinia's core.

It appears that the east coast of Laurentia lay adjacent to the west coast of South America, while a conjoined Australia and Antarctica seem to have lain against the proto-North American west coast. A third craton, what would become north-central Africa, was caught in between these two colliding masses..

Other cratons such as the Kalahari (southern Africa), the Congo (west-central Africa), and the San Francisco (southeastern South America), appear to have been separate from the rest of Rodinia.

Paleogeografi

Rodinia's landmass was probably centered selatan of the ekuator. Because Earth was at that time experiencing the Cryogenian period of glaciation, and temperatures were at least as cool as today, substantial areas of Rodinia may have been covered by glaciers or the southern polar ice cap. The interior of the continent, being so distant from the temperature-moderating effects of the ocean, was probably seasonally extremely cold (see continental climate). It was surrounded by the superocean geologists are calling Mirovia (from mir, the Russian word for "globe").

Cold temperatures may have been exaggerated during the early stages of continental rifting. Geothermal heating peaks in crust about to be rifted; and since warmer rocks are less dense, the crustal rocks rise up relative to their surroundings. This rising creates areas of higher altitude, where the air is cooler and ice is less likely to melt with changes in season, and it may explain the evidence of abundant glaciation in the Ediacaran period.

The eventual rifting of the continents created new oceans, and seafloor spreading, which produces warmer less-dense rock, probably increased sea level by displacing ocean water. The result was a greater number of shallower oceans.

The evaporation from these oceans may have increased rainfall, which, in turn, increased the weathering of exposed rock. By inputting data on the ratio of stable isotopes ¹⁸O:¹⁶O into computer models, it has been shown that in conjunction with quick-weathering of volcanic rock, this increased rainfall may have reduced greenhouse gas levels to below the threshold required to trigger the period of extreme glaciation known as Snowball Earth.

All of this tectonic activity also introduced into the marine environment biologically important nutrients, which may have played an important role in the development of the earliest animals.

Lihat pula

• Pangea
• Daftar superbenua
• Mesoproterozoikum

Pranala luar

• (Inggris) Return to Precambrian
• (Indonesia) Rodinia