How the Greeks Knew the Earth was a Sphere


‘As long ago as 340 BC the Greek philosopher Aristotle, in his book On the Heavens,
was able to put forward two good arguments for believing that the earth was a round sphere rather than a Hat plate. First, he realized that eclipses of the moon were caused by the earth coming between the sun and the moon. The earth’s shadow on the moon was always round, which would be true only if the earth was spherical. If the earth had been a flat disk, the shadow would have been elongated and elliptical, unless the eclipse always occurred at a time when the sun was directly under the center of the disk. Second, the Greeks knew from their travels that the North Star appeared lower in the sky when viewed in the south than it did in more northerly regions. (Since the North Star lies over the North Pole, it appears to be directly above an observer at the North Pole, but to someone looking from the equator, it appears to lie just at the horizon. From the difference in the apparent position of the North Star in Egypt and Greece, Aristotle even quoted an estimate that the distance around the earth was 400,000 stadia. It is not known exactly what length a stadium was, but it may have been about 200 yards, which would make Aristotle’s estimate about twice the currently accepted figure. The Greeks even had a third argument that the earth must be round, for why else does one first see the sails of a ship coming over the horizon, and only later see the hull?’

– Hawking. S. (1998) A Brief History of Time New York, United States: Bantam Books p. 2

The Human Race


The thinking ape
200,000 years ago

Our species, Homo sapiens, is ridiculously young. We have only existed for a fifth of a million years. In that time we have expanded from our African birthplace to reach every continent, and even outer space. Our activities have precipitated the sixth mass extinction and unleashed the fastest episode of climate change in Earth’s history. Yet we are also the only species that has ever managed to piece together the history of Earth.

See other: History of Life

The First Hominids


The road to humanity
13-7 million years ago

The first apes appeared in Africa around 25 million years ago. Then at some point, the group split into the ancestors of modern humans and the ancestors of modern apes. It is hard to say exactly when, but thanks to modern genetics and a host of fossil discoveries, we have a rough idea. The oldest known hominid was Sahelanthropus tchadensis, which lived about 7 million years ago.

See other: History of Life

C4 Photosynthesis


Supercharged plants
32-25 million years ago

Plants have been busily harnessing sunlight to make sugar for hundreds of millions of years – a process called photosynthesis. But fairly recently, some plants have found a better way to do it. C4 photosynthesis is far more efficient than normal photosynthesis, allowing C4 plants to cope with harsh conditions. Today scientists are trying to engineer rice to use C4 photosynthesis, to help feed the growing population.

See other: History of Life

Shakespeare on Astrology


Edmund ‘This is the excellent foppery of the world, that, when we are sick in fortune,—often the surfeit of our own behaviour,—we make guilty of our disasters the sun, the moon, and the stars; as if we were villains on necessity; fools by heavenly compulsion; knaves, thieves, and treachers by spherical pre-dominance; drunkards, liars, and adulterers by an enforced obedience of planetary influence; and all that we are evil in, by a divine thrusting on: an admirable evasion of whoremaster man, to lay his goatish disposition to the charge of a star! My father compounded with my mother under the dragon’s tail, and my nativity was under ursa major; so that it follows I am rough and lecherous.—Tut!’

– Reed International Books Ltd. 1992. The Illustrated Stratford Shakespeare London, Great Britain: Chancellor Press (1996) p. 836

Death of the Dinosaurs


The fifth extinction
65 million years ago

Boom. Extinction. 65 million years ago, a huge chunk of rock from outer space smashed into what is now Mexico. The explosion was devastating, but the longer-term effects were worse. Dust was thrown into the upper atmosphere and blocked out sunlight, and in the ensuing cold and darkness Earth suffered its fifth and last mass extinction. The dinosaurs were the most famous casualties, but pterosaurs and giant marine reptiles were also wiped out.

See other: History of Life

Conversations: Arrogant Scientists?


Helena
As many critics of religion have pointed out, the notion of a creator poses an immediate problem of an infinite regress. If God created the universe, what created God?

Galene
The God of most monotheists is believed to be an uncreated entity.

Sappho
To say that God, by definition, is uncreated simply begs the question. The truth is that no one knows how or why the universe came into being. It is not clear that we can even speak coherently about the creation of the universe, given that such an event can be conceived only with reference to time, and here we are talking about the birth of space-time itself.

Helena
The physicist Stephen Hawking, for instance, pictures space-time as a four dimensional, closed manifold, without beginning or end (much like the surface of a sphere). Having said that, any intellectually honest person will admit that he does not know why the universe exists. Scientists, of course, readily admit their ignorance on this point. Religious believers do not. Continue reading

The First Mammals


Hairy beasts
220 million years ago

At the same time that the dinosaurs were spreading and diversifying, the first mammals evolved. Their ancestors were reptiles called cynodonts, whose faces looked a little like those of dogs and may have had fur or whiskers. Early mammals such as Morganucodon were small and shrew-like, and probably only active at night. This may have spurred them to evolve warm-bloodedness: the ability to keep their body temperature constant.

See other: History of Life