Gts 2

• In classical Greek philosophy, the Earth was eternal, making the Age of the Earth irrelevant.
• Time is a circle with no beginning and no end.
• In 1654, Bishop Ussher calculated that the Earth was created in 4004 BC using evidence from the Bible and other Middle Eastern literature.
• The date of 4004 BC became so popular that it was printed with the Book of Genesis.
• Comte de Buffon hypothesized that the Earth had originated as a fiery ball after a comet had collided with the Sun.
• In 1760, Buffon measured the cooling time of red-hot iron balls of different sizes, scaled up to the size of the Earth.
• Hermann von Helmholtz calculated the time it would take for the sun to condense to its present diameter from a gas nebula, around 20 million years.
• Lord Kelvin assumed that Earth originally had a temperature of 7000 ° F molten, applying his knowledge of how fast heat is conducted through rocks: geothermal gradient (1 ° F/50 ft).
• Lord Kelvin calculated the cooling age of the Earth to be 20 million years.
• The discovery of radioactivity in the early twentieth century showed that the Earth was also producing some heat, indicating that the Earth must have been much older than allowed by Lord Kelvin’s calculations.
• Charles Lyell, a geologist, thought that the key to understanding the age of the Earth might lie in the way that mountains slowly erode down.
• Lyell thought that the rate at which the erosion and deposition of sediment occurs had stayed more or less constant through geological time.
• Charles Lyell, a British geologist, studied fossil seashells in Tertiary rocks in France.
• James Hutton recognized that sediment is not deposited continuously in the real world, but rather through convulsions of the Earth’s crust, sediments are laid down as horizontal layers in the sea which might be pushed up to form mountains.
• Abraham Werner argued that all rocks had been deposited in a worldwide ocean, a concept known as Neptunism.
• William Smith used fossils to check that the age of rocks in one area was the same at the rocks in another.
• James Hutton also recognized that there were big gaps in the geological record, which he referred to as 'the abyss of time'.
• Georges Cuvier, a French naturalist, studied remains of fossil and living elephants and convincingly showed that animals like the woolly mammoth had gone extinct.
• Two Wernerian terms for the youngest rocks on our planet are Tertiary and Quaternary.
• William Smith produced a complete geological map of Britain, showing the relative order in which the rocks of Britain formed and whether there were any big time gaps within the succession.
• William Smith, a surveyor, realized that sequences of different rocks occurred in the same order in different places, and to be sure that a rock type in one place was the same as a rock type in another, he compared the fossils that they contained.
• Radiometric dating of meteorites date the formation of the Solar System and Earth to 4550 million years old.
• Our solar system and the Earth in it formed out of a nebula about 4550 million years ago.
• Well-dated fossils indicate that the first life had appeared by 3800 million years ago and had evolved into complex cells by 2500 million years ago.
• One large meteorite was found in the Canyon Diablo region of Arizona in southwest USA, probably crashed to Earth about 20,000 years ago but that it had been wandered through space for much longer than that.
• Although late arrivals, humans have transformed the Earth’s biosphere and climate to a unique degree.
• Radiometric dating has transformed our understanding of the age and history of our planet, allowing us to know the relative order in which events happened and when they occurred on an absolute timescale.
• The first large animals arrived on the scene 800 million years ago and the famous dinosaurs had their day about between 65 and 180 million years ago.
• Humans are a dramatic late arrival, appearing only in the last blink of geological time, some 2 million years ago.
• Radiometric dating of the meteorite gives a maximum age of 4550 million years, indicating that the solar system and the Earth in it had formed by 4550 million years ago (4.55 billion years ago).
• The mineral flake found at Jack Hills, Australia, tells us that the Earth had cooled down sufficiently to form a crust as early as 4404 million years ago, as little as 150 million years after the formation of the Earth.
• All these estimates were based on assumptions that couldn’t be proven.
• One of the first people to try and understand the history of our planet was a Danish priest called Nicolas Steno (1638 - 1686), who argued that sediment gradually built up on the sea floor as layers which are both laterally continuous and horizontal.
• Unfortunately, what Joly didn’t realize is that salt doesn’t simply accumulate in the oceans over time, there are geological processes that are constantly taking salt out of the oceans.
• Geologists believe this ‘mass extinction’ was caused by a giant meteorite colliding with the Earth.
• In 1899, John Joly calculated the Earth’s age using the saltiness of the ocean, resulting in an age ranging between 80 - 150 million years.
• Geologists decide to place the boundary between one geological period and the next usually positioned where there is an abrupt change in the kinds of fossils in the rock or a change in the ancient climate or environment.
• Charles Lyell used the proportion of living fossils to divide up geological time.
• The term geological history refers to the sequence of historical events from the formation of the Earth to the present day.
• Georges Cuvier showed that the oldest rocks contained mostly extinct shells while the youngest rocks contained shells similar to those living today.