Heat supplies the energy that causes motion. The deeper you go into toward the Earths core, the hotter it gets. At the core it is really hot. All that heat tries to rise toward the surface. In the Mantle, the rock is partially melted and is able to move. As it is heated, the material in the mantle moves toward the surface. As the mantle material rises, it cools. When it reaches the Earths crust, it is mostly stopped. A little of the material can break through the surface, but not all. Instead, it begins to move horizontally. The mantle material moves horizontally away from a mid-ocean ridge crest. Toward the surface, the mantle material starts to cool. As it cools it sinks back down into the mantle. These areas are where deep sea trench occur. The material sinks back down to the core. The system operates like a giant conveyor belt. The motion due to heating and cooling is called convection. 

Question: "What kind of feature occurs where cooled mantle material sinks back down into the mantle?"

Response: "Deep sea trench"

A: yes


The inhabited history of the Las Vegas Valley stretches to 23,000 b.c. , when much of the area was covered by a prehistoric lake. During this period, the indigenous people lived in caves, hunting the mammals that gathered at the shoreline. The landscape of the valley changed dramatically over the next 200 centuries. The glaciers feeding the lake melted away and the lake evaporated. Fossils tell an obscure story of man's slow and sporadic development. Around 3000 b.c. , native Archaic Indians began to develop a lasting hunting and gathering culture. By this time, the valley was in much the same geographic state as it exists in today, with one exception — the presence of artesian springs that bubbled to the surface in several areas. These springs fed a network of streams draining through the Las Vegas Wash to the Colorado River. The areas surrounding the springs were desert oases: sprawling collections of grasses, trees, and wildlife. Many springs lay in areas that would eventually become the center of the modern Las Vegas metropolis. For about 4000 years, the Archaics thrived in a culture that included many signs of early civilization. Signs of even more advancement appeared halfway through the first millennium a.d. , when the Anasazi Indians inhabited the valley. Far more progressive than the Archaics, the Anasazi utilized such formal agricultural techniques as irrigation to assist their harvest. This permitted the Anasazi to achieve a benchmark of advanced society — the ability to live in permanent shelters year-round without need to follow wildlife. Mysteriously, the Anasazi vanished from the valley around a.d. 

Question: "What permitted the Anasazi to achieve a benchmark of advanced society?"

Response: "Usage of saltpeter"

A: no


The French have always wanted to know what it means to be a French­man. Their history has been a constant quest for national identity: a conflict between strong regional loyalties and central authority. In about 2000 b.c. Celtic tribes — probably from eastern Europe — came looking for greener pastures in the areas that are now Franche-Comté, Alsace, and Bur­gundy. At the same time, migrants from the Mediterranean countries were trickling into the south. The first recorded settlement was the trading post set up by Phocaean Greeks from Asia Minor at Massalia (Mar­seilles) around 600 b.c. , followed by other ports at Hyères, Antibes, and Nice. But the Greeks developed few contacts with the interior beyond a little commerce in olives and wine with the Celts of Burgundy. When their position was threatened by Ligurian pirates at sea and warlike tribes from inland, the merchants of Marseilles called on Rome for help. From Gaul to France In 125 b.c. , the Romans came in force, conquered the "Gallic barbarians," and set up a fortress at Aquae Sextiae (Aix-en-Provence). They took advantage of this new stronghold to create Provincia (now Provence), stretching from the Alps to the Pyrénées, in order to guarantee communications between Italy and Spain. When this province was endangered by fresh attacks from the north, Julius Caesar himself took charge, conquering practically the whole of Gaul by 50 b.c. Caesar drew Gaul's northeastern frontier at the Rhine, taking in present-day Belgium, and warned that the Ger­man­ic tribes across the river — the Franks (after whom France is named), Alamans, and Saxons — would always threaten the security of the frontier. The Romanization of Gaul sent the most energetic warriors to defend the outposts of the empire while their families settled down to work the land or build towns such as Lyon, Orange, Arles, and Nîmes, and the first great highways between them. At the same time, merchants built up a thriving trade with the rest of the Roman Empire. The pattern for the peasantry and bourgeoisie of France was thus established. Christianity was introduced into Gaul in the first century a.d. 

Question: "About what year, did Celtic tribes came looking for greener pastures in the areas that are now Franche-Comté, Alsace, and Bur­gundy?"

Response: "2000 BC"

A:
yes