Reading

[1] The nebular hypothesis suggests that our solar system was formed from nebulous material or clouds of gas and dust. In 1755, Immanuel Kant proposed this theory in his book, Universal Natural History and Theory of the Heaven. This planetary system formation is now considered to be at work throughout the cosmos. The nebular hypothesis is also called the solar nebular disk model or simply solar nebular model. The theory suggests that stars form in huge, dense clouds of gas. The gas is comprised of molecular hydrogen. Within these clouds, matter or substance forms into small, rotating clumps that develop into stars. A ring of gas encircles these stars. This process may cause the formation of planets too.

[2] Generally, it takes about 1 million years for a star to form. Within 10 to 100 million years, a system will evolve out of the protoplanetary disk. The protoplanetary disk feeds the central star. It is very hot when first formed and then cools to develop the T Tauri star stage; at this point, small dust grains made of rocks and ice may form. These grains may transform into planetesimals, smaller planets, and moons. This stage takes 100 million to a billion years.

[3] Giant planets form in a more complicated way. It is believed to happen beyond the frost line where planetary embryos consist of different sorts of ice. Consequently, these formations are much larger than in the inner part of the protoplanetary disk. Some embryos seem to continue to form. The accumulation of gas continues for several million years although planets like Jupiter- and Saturn-are considered to have accumulated their mass over only 10,000 years.

[4] The formation of stars is a consequence of accretion disks around younger stellar objects. Study of these disks indicates that the dust grains inside grow in size on short time scales, producing 1 centimeter-sized particles. This accretion process, by which kilometre-sized planetesimals grow into much larger bodies, is better understood now. This process forms inside any disk where the number density of planetesimals is high enough and continues. Development slows down and the result is the development of planetary embryos of different sizes. Simulations have shown that the merger of these embryos in the inner part of the protoplanetary disk leads to the creation of small Earth-sized planets. Therefore, we now understand the development of these planets.

[5] Stars are believed to be formed inside giant clouds of cold molecular hydrogen, 300,000 times the mass of the Sun. Over millions of years, these giant molecular clouds collapse and separate. These cloud fragments develop small, dense cores, which then collapse into stars. The cores vary in size and are called protostellar nebulae.

[6] As indicated by the solar nebular disk model, rocky planets are created in the inner part of the protoplanetary disk, within the frost line, where the temperature is high enough to stop condensation of water ice and other substances into grains. This results in a transformation of purely rocky grains and then in the creation of rocky planetesimals.

[1] The Stone Age consists of seven subdivisions, including the Paleolithic Age (from 2 million to 10,000 years BC) – about 3000 years after the Ice Age – and The Neolithic period (‘New’ Stone Age), from 1000 to about 2,500BC. The discovery of fossils indicates that scavenging and hunting began in the Stone Age. However, researchers believe that early humans lived not only on meat but also on plants from foraging in the forest. Ancient humans used skins and mats – made of leaves – to collect plants such as berries, seeds, and fruit. Archaeologists think that people used doughnut-shaped stones to serve as weights to make wooden digging sticks effective.

[2] The vast caverns of Lascaux, discovered in 1940, reveal the earliest human works of art. Along with the cave paintings of Spain and the discovery of stone tools, there is much evidence for the rich skills and culture that date back to ancient civilization. The art of stone tool-making first appeared around 2 million years ago. Many tools, however, were not just made of stone but also of bone, skin, and wood. Ancient humans used these tools to pulverize grain, cut grass and chop meat for cooking and eating.

[3] During the Stone Age, the development of domesticated plants is considered to have occurred in two stages: firstly, taking plant cuttings, particularly vines and root crops and secondly, using seeds based on grains which are more common in temperate zones. Starchy yams have been grown and processed as far back as 100,000 years ago in the Middle Stone Age. Observation and evidence date the consumption of yams back to Neanderthals in fact, as proven with fossilized deposits of yams in the teeth and gums of Neanderthal remains. Furthermore, archaeologists, such as Julio Mercader, have recovered several stone tools from caves in Mozambique that indicate that wild sorghum, bananas and wild oranges were consumed by humans.

[4] Cooking food makes it tastier to eat and easier to digest. Cooking could have been discovered by accident after wildfires burned food. Evidence of cooking, however, dates back to 12,500 years ago with the discovery of clay cooking pots in East Asia. Early cave art suggests that men hunted and women gathered food. Early foragers lived together to defend themselves from predators. People built huts to protect themselves from harsh weather and climate, and they used animal skins as clothing. The earliest clothing actually dates back to 26,000 years ago. As groups spent only a few hours searching for food and shelter, they would have had plenty of time for tool-making, socializing and artistic pursuits.

[5] The beginnings of science, art, and religion lie in the Stone Age period. People learned which plants were edible, developed herbal remedies and an awareness of the use of plants for other purposes began. Stone Age people studied the behaviour of animals, experimented with material for clothing and began to identify minerals for paint and tools.

[6] The cavern paintings in European and North Africa show hunting scenes as well as people dressed in animal skins and paint, such as the cave of at Vallon Pont-d’Arc in southern France. Researchers suggest that these markings show the first attempt at writing and counting. Religious belief at this time is unclear, although graves from around 100,000 years ago have stone implements and red-ochre powder, showing a reverence for their leaders and a possible belief in immortality.