Pre-Tolstojan, also Pretolstojan Period, refers to the oldest period of the history of Mercury, 4500–3900 MYA. It is the "first period of the Eomercurian Era and of the Mercurian Eon, as well as being the first period in Mercury's geologic history", and refers to its formation and the 600 million or so years in its aftermath. Mercury was formed with a tiny crust, mantle, and a giant

core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...

and as it evolved it faced heavy bombardments that created most of the craters and intercrater plains seen on the planet's surface today. Many of the smaller basins and

multi-ring basins A multi-ringed basin (also a multi-ring impact basin) is not a simple bowl-shaped crater, or a peak ring crater, but one containing multiple concentric topographic rings; a multi-ringed basin could be described as a massive impact crater, surrou ...

were created during this period. Considered a "dead" planet, its geology is highly diverse with craters forming the dominant terrain. The name Pre-Tolstojan refers to the Tolstoj crater on the surface of Mercury, which is believed to have been formed in an impact event circa 3900 MYA. The latter has been named after the Russian writer

Leo Tolstoy Count Lev Nikolayevich TolstoyTolstoy pronounced his first name as , which corresponds to the romanization ''Lyov''. () (; russian: link=no, Лев Николаевич Толстой,In Tolstoy's day, his name was written as in pre-refor ...

History

The history of Mercury is divided into five periods; Pre-Tolstojan is the first epoch, the other four are Tolstojan, Calorian, Mansurian, and Kuiperian. Pre-Tolstojan stage I represents the formation stage of Mercury when it evolved as a tiny crust, mantle, and a giant core. During this period, multi-ring basins were created due to bombardment and concurrently formation of craters and intercrater plains also occurred. The location of Lobate scarps and their relative age, overlaid on a geometric map of Mercury using Mariner 10 mosaics indicate that these formations occurred in pre-Tolstojan intercrater plains, and later during the Tolstojan and Calorian periods.

Geology

Based on surface geology and

albedo Albedo (; ) is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body that refl ...

the sequence of creation of Mercury has been recorded and compared with that of the formation epochs of the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

which show some similarities. The mapped region of Mercury shows intercrater plains, basins, smooth plains, craters and

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

features. The earliest formation recorded is that of multi-ring basins (less than diameter) during the Pre-Tolstojan epoch; the morphologic features indicate domination of a single ring formation. The intercrater plains lie between and amidst large craters. Lobate scarps, seen extensively on planet Mercury, are in the form of undulating to arcuate scarps; wrinkle ridges are observed in the smooth plains materials. The basins of less than diameter are presumed to have disappeared during the bombardment. The formations in the order of their earliest occurrence, compared with lunar counterparts (indicated within brackets) are: Pre-Tolstojan period with formations of inter-crater plains, multi-ring basins and crater materials (pre-Nectarian more than 4.5 GA); Tolstojan period with Goya formations (Tolstoj Basin deposits), Plains, small Basin Plains and Crater materials (Nectarian, 4.2 to 3.8 GA); Calorian period of Caloris group (including secondaries and ridges), Caloris structured plains, Caloris smooth plains, Crater and small basin material (Imbrian, 3.87 to 3.75 GA), Mansurian with slightly degraded crater materials (Eratospheries, 3.24 to 3.11 GA); and Kulperian of bright rayed craters (Kulper is an example), and crater materials (Copernican, 2.2 to 1.25 GA).

References

{{reflist Geology of Mercury