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The first eon in Earth's history, the Hadean, begins with the Earth's formation and is followed by the Archean eon at 3.8 Ga. [2]: 145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, [34] [35] [36] soon after the formation of the Earth's crust and the Earth
From ancient times, people suspected that the climate of a region could change over the course of centuries. For example, Theophrastus, a pupil of Ancient Greek philosopher Aristotle in the 4th century BC, told how the draining of marshes had made a particular locality more susceptible to freezing, and speculated that lands became warmer when the clearing of forests exposed them to sunlight.
Before, different aspects of Earth's climate history were studied by a variety of disciplines. [5] At the end of the 20th century, the empirical research into Earth's ancient climates started to be combined with computer models of increasing complexity.
[45] [46] This is equivalent to a change of the semiminor axis of the planet's orbit from 99.95% of the semimajor axis to 99.88%, respectively. [47] Earth is passing through an ice age known as the quaternary glaciation, and is presently in the Holocene interglacial period. This period would normally be expected to end in about 25,000 years. [42]
Global change in broad sense refers to planetary-scale changes in the Earth system. It is most commonly used to encompass the variety of changes connected to the rapid increase in human activities which started around mid-20th century, i.e., the Great Acceleration .
Climate change can also be used more broadly to include changes to the climate that have happened throughout Earth's history. [32] Global warming—used as early as 1975 [33] —became the more popular term after NASA climate scientist James Hansen used it in his 1988 testimony in the U.S. Senate. [34] Since the 2000s, climate change has ...
In other words, any geologic processes at work in the present have operated in the same ways throughout geologic time. This enables those who study Earth history to apply knowledge of how the Earth's processes operate in the present to gain insight into how the planet has evolved and changed throughout long history.
He observed the composition of the land and formulated a theory where the Earth changes at a slow rate and that these changes cannot be observed during one person's lifetime. Aristotle developed one of the first evidence-based concepts connected to the geological realm regarding the rate at which the Earth physically changes. [5] [6]