Deep time

Deep time is the idea, held to be credible by natural researchers since the early 19th century, that the Earth is millions or billions of years old, rather than the few thousand that young Earth creationism claims.

History
The concept was first formally proposed by James Hutton, a Scottish geologist, in 1788. Hutton and his various contemporaries challenged the then-standard concept of a 6,000 year old Earth by studying the geological strata and stating he could find no rational "beginning of time", if layers were consistently formed, a basis of Lyell's Uniformitarianism. The continuing process whereby rocks are eroded and new sedimentary rocks form out of the remains of older eroded rocks was previously known. Hutton, however, observed further this process takes so long that the Earth must be much older than a few thousand years. Although he was an absolutely terrible writer, his friends translated his observations into something at least somewhat readable so it could reach a broader audience.

Evidence
Evidence for deep time includes:
 * Geological strata
 * Geological formations, like canyons cut by rivers, and the Triassic Cliffs cut by the sea.
 * Fossil records, though there is large dependence on the geological strata, for fossils to "prove" an age of the Earth.
 * Radiometric dating systems, which use the constant rate of radioactive decay of unstable nuclides in the Earth's crust to place the age of the Earth at 4.5 billion years.
 * Dating of the Sun and Moon
 * Dating of the formation of our Solar system
 * Evidence for the age of the Universe

Other uses
In cosmology, "deep time" can mean forecasts about the ultimate fate of the universe. Such forecasts often look trillions of years into the future, many many times the universe's current age.