Another photograph of the Parthenon:
Formation[ edit ] The Solar System formed from a dust cloud that was at least partially the remnant of one or more supernovas that created heavy elements by nucleosynthesis. Grains of matter accreted through electrostatic interaction.
As they grew in mass, gravity took over in gathering yet more mass, releasing the potential energy of their collisions and in-falling as heat.
The protoplanetary disk also had a greater proportion of radioactive elements than the Earth today because, over time, those elements decayed. Their decay heated the early Earth even further, and continue to contribute to Earth's internal heat budget.
The early Earth was thus mostly liquid. A sphere is the only stable shape for a non-rotating, gravitationally self-attracting liquid. The outward acceleration caused by the Earth's rotation is greater at the equator than at the poles where is it zeroso the sphere gets deformed into an ellipsoidwhich represents the shape having the lowest potential energy for a rotating, fluid body.
This ellipsoid is slightly fatter around the equator than a perfect sphere would be. Earth's shape is also slightly lumpy because it is composed of different materials of different densities that exert slightly different amounts of gravitational force per volume. The liquidity of a hot, newly formed planet allows heavier elements to sink down to the middle and forces lighter elements closer to the surface, a process known as planetary differentiation.
This event is known as the iron catastrophe ; the most abundant heavier elements were iron and nickelwhich now form the Earth's core.
History of Earth Later shape changes and effects[ edit ] Though the surface rocks of the Earth have cooled enough to solidify, the outer core of the planet is still hot enough to remain liquid. Energy is still being released; volcanic and tectonic activity has pushed rocks into hills and mountains and blown them out of calderas.
Meteors also create impact craters and surrounding ridges. However, if the energy release ceases from these processes, then they tend to erode away over time and return toward the lowest potential-energy curve of the ellipsoid. Weather powered by solar energy can also move water, rock, and soil to make the Earth slightly out of round.
Earth undulates as the shape of its lowest potential energy changes daily due to the gravity of the Sun and Moon as they move around with respect to the Earth.
This is what causes tides in the oceans ' water, which can flow freely along the changing potential.
The same spheroidal shape can be seen from smaller rocky planets like Mars to gas giants like Jupiter. These come in many non-spherical shapes which are lumpy masses accreted haphazardly by in-falling dust and rock; not enough mass falls in to generate the heat needed to complete the rounding.
Some SSSBs are just collections of relatively small rocks that are weakly held next to each other by gravity but are not actually fused into a single big bedrock. Some larger SSSBs are nearly round but have not reached hydrostatic equilibrium. The small Solar System body 4 Vesta is large enough to have undergone at least partial planetary differentiation.
Stars like the Sun are also spheroidal due to gravity's effects on their plasmawhich is a free-flowing fluid. Ongoing stellar fusion is a much greater source of heat for stars compared to the initial heat released during formation.
Effects and empirical confirmation[ edit ] The roughly spherical shape of the Earth can be confirmed by many different types of observation from ground level, aircraft, and spacecraft.
The shape causes a number of phenomena that a flat Earth would not. Some of these phenomena and observations would be possible on other shapes, such as a curved disc or torusbut no other shape would explain all of them. Spacecraft[ edit ] Many pictures have been taken of the entire Earth by satellites launched by a variety of governments and private organizations.
From high orbits, where half the planet can be seen at once, it is plainly spherical. The only way to piece together all the pictures taken of the ground from lower orbits so that all the surface features line up seamlessly and without distortion is to put them on an approximately spherical surface.
Astronauts in low Earth orbit can personally see the curvature of the planet, and travel all the way around several times a day.Classical Antiquity in the Mediterranean region is commonly considered to have begun in the 8th century BC (around the time of the earliest recorded poetry of Homer) and ended in the 6th century AD.
Classical Antiquity in Greece was preceded by the Greek Dark Ages (c.
– c. BC), archaeologically characterised by the protogeometric and . Draco, also a figure from the 7th century BC, was responsible for the BC Draconian Laws in Athens. Draco liked to keep things simple and prescribed the death penalty for pretty much any criminal offense.
Solon, who lived BC, was the man who revised Draco's law code and made it a bit more kaja-net.com was the set of reforms known as Solon's Laws. Beginning at a date difficult to fix precisely (at the end of the 7th or during the 6th century), Athens, in contrast to Sparta, became the first to renounce education oriented toward the future duties of the kaja-net.com Athenian citizen, of course, was Physical and human geography.
The earliest reliably documented mention of the spherical Earth concept dates from around the 6th century BC when it appeared in ancient Greek philosophy but remained a matter of speculation until the 3rd century BC, when Hellenistic astronomy established the spherical shape of the Earth as a physical given.
The paradigm was gradually adopted throughout the Old World during Late Antiquity and. The Milesian School: 7th-6th Centuries BCE Miletus was an ancient Greek Ionian city-state on the western coast of Asia Minor in today’s Turkey.
The Milesian School consisted of Thales, Anaximander, and Anaximenes (all from Miletus). The contribution of Greece: 7th - 5th century BC No place or period has been so influential in the history of architecture as Greece in the 7th to 5th centuries BC.