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Glossary radiometric dating

glossary radiometric dating-88

The Archean and Proterozoic eons follow; they produced the abiogenesis of life on Earth and then the evolution of early life.

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Species continue to evolve, taking on new forms, splitting into daughter species or going extinct in the process of adapting or dying in response to ever-changing physical environments.Hominins, the earliest direct ancestors of the human clade, rose sometime during the latter part of the Miocene epoch; the precise time marking the first hominins is broadly debated over a current range of 13 to 4 million years ago.The succeeding Quaternary period is the time of recognizable humans, i.e., the genus Homo, but that period's two million-year-plus term of the recent times is too small to be visible at the scale of the GTS graphic.The process of plate tectonics continues to shape the Earth's continents and oceans and the life they harbor.Human activity is now a dominant force affecting global change, adversely affecting the biosphere, the Earth's surface, hydrosphere, and atmosphere, with the loss of wild lands, over-exploitation of the oceans, production of greenhouse gases, degradation of the ozone layer, and general degradation of soil, air, and water quality.Each eon saw the most significant changes in Earth's composition, climate and life.

Each eon is subsequently divided into eras, which in turn are divided into periods, which are further divided into epochs. The moon is formed around this time, probably due to a protoplanet's collision into Earth.

The atmosphere is composed of volcanic and greenhouse gases.

Eukaryotes, a more complex form of life, emerge, including some forms of multicellular organisms.

Gradually, life expands to land and all familiar forms of plants, animals and fungi begin appearing, including annelids, insects and reptiles.

Several mass extinctions occur, among which birds, the descendants of dinosaurs, and more recently mammals emerge.

Complex life, including vertebrates, begin to dominate the Earth's ocean in a process known as the Cambrian explosion.