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This model posits that, 4.6 billion years ago, the Solar System was formed by the gravitational collapse of a giant molecular cloud spanning several light-years. Many stars, including the Sun, were formed within this collapsing cloud. The gas that formed the Solar System was slightly more massive than the Sun itself.
According to evidence from radiometric dating and other sources, Earth formed about 4.54 billion years ago. [7] [8] [9] The current dominant theory of planet formation suggests that planets such as Earth form in about 50 to 100 million years but more recently proposed alternative processes and timescales have stimulated ongoing debate in the planetary science community. [10]
4.6 billion years Today: Sun remains a main-sequence star. [117] 6 billion years 1.4 billion years in the future Sun's habitable zone moves outside of the Earth's orbit, possibly shifting onto Mars's orbit. [120] 7 billion years 2.4 billion years in the future The Milky Way and Andromeda Galaxy begin to collide. Slight chance the Solar System ...
The closest well-measured approach was Scholz's Star, which approached to ~ 50,000 AU of the Sun some ~70 thousands years ago, likely passing through the outer Oort cloud. [267] There is a 1% chance every billion years that a star will pass within 100 AU of the Sun, potentially disrupting the Solar System. [268]
In physical cosmology, the age of the universe is the time elapsed since the Big Bang: 13.8 billion years. [1] Astronomers have two different approaches to determine the age of the universe . One is based on a particle physics model of the early universe called Lambda-CDM , matched to measurements of the distant, and thus old features, like the ...
The universe has appeared much the same as it does now, for many billions of years. It will continue to look similar for many more billions of years into the future. The galactic disk of the Milky Way is estimated to have been formed 8.8 ± 1.7 billion years ago but only the age of the Sun, 4.567 billion years, is known precisely. [69]
In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. [19] [20] He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface temperature gradient to decrease to its present value.
Perhaps unsurprisingly, our universe has just the right mass–energy density, equivalent to about 5 protons per cubic meter, which has allowed it to expand for the last 13.8 billion years, giving time to form the universe as observed today. [65] [66] There are dynamical forces acting on the particles in the universe which affect the expansion ...