Empedocles (around 490 to 444 BC) thought there were four original elements: Earth, Air, Fire, Water. He thought everything else came about through their combination and/or separation by the two opposite principles of Love and Strife.
Leucippus (around 460 to 420 BC) and Democritus (around 460 to 370 BC), supposedly a pupil of Leucippus, are considered the founders of atomism. Leucippus regarded atoms as imperceptible, individual particles that differ only in shape and position.
Plato (about 427 to 347 BC) in his work, the Timaeus, proposes a mathematical construction of the elements - earth, air, fire, water. Each of these elements is said to consist of particles or primary bodies. Each particle is a regular geometrical solid- the cube, tetrahedron, octahedron and icosahedron. Each of these particles is composed of simple right triangles. The particles are like the molecules of the theory; the triangles are its atoms.
Plato's beliefs as regards the universe were that the stars, planets, Sun and Moon move round the Earth in crystalline spheres. The sphere of the Moon was closest to the Earth, then the sphere of the Sun, then Mercury, Venus, Mars, Jupiter, Saturn and furthest away was the sphere of the stars. He believed that the Moon shines by reflected sunlight.
Aristotle (384-322 BC) said that Earth was both the centre of the universe and one of the four primordial elements. He saw the universe as a series of concentric spheres, with earth at the centre, followed by water, air, fire. The harmonious relationships and interworkings of these spheres could be heard as celestial music: the music of the spheres. Above fire was the Moon, and this sphere delimited matter of a different kind. Beyond the Moon were spheres for the Sun, the planets, and the stars, which were carried around the Earth in daily, complicated orbits. All matter inside of the Moon’s orbit was different in kind from matter above the Moon. Reminiscent of Plato’s ideas, Aristotle’s theory said that terrestrial matter decays and is ephemeral, while celestial matter, the aether, is unchanging and eternal