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The Planet Earth is about 4.55 billion years old. Based on current understanding of planet formation, it would be difficult to pinpoint a specific year when the earth formed, since the formation of the earth involved a long and slow accumulation of comets, meteors, asteroids, planetesimals, dust, and gasses. These raw materials that made up our planet were left over from previous stars that had exhausted their fuel and generated elements other than helium and hydrogen in explosive nuclear reactions late in their stellar lives. As a clump of star dust (called a “nebula” or “molecular cloud”) accumulated into our solar system, most of the matter ended up bunching together in the sun, which is about 4.5 to 5 billion years old.

Toward the later stages of the sun’s formation, the planets would have formed. They would have formed partly as the tempertures cooled away from the sun because the sun was sucking up the mass and getting hotter, leaving matter out in what became the solar system a bit cooler (Clair Cameron Patterson determined condensation of matter began between 4.480 and 4.620 billion years ago. Closer to the sun, heavier compounds and atoms clumped together, while further out, light ices (water ice as well as frozen ammonia and methane) formed. Gravity pulled together materials, and sometimes planetoids collided in this early solar system. The earth would have emerged in this protoplanetary disk for millions of years as planets and moons condensed and accumulated mass through accretion of material orbiting the young sun.

Links about the age of the Earth:
  1. Baylor University’s department of geology offers a fine summary of various studies showing the age of the earth, and they offer a good reference list
  2. Lecture notes from Ann Zabludoff on the nebular theory of the origin of the solar system.
  3. The “Mathematics of Planet Earth” website hosted at Rutgers University offers a short description of Lord Kelvin’s early estimates of the age of the earth and why they were wrong.
  4. James Schombert at the University of Oregon publishes a lecture on the history of earth in which he goes over various past estimates of the earth’s age (not just Lord Kelvin’s) and explains how we understand past estimates didn’t quite get it right. .
  5. The Talk Origins website has a page devoted to the scientific determination of the age of the earth.
  6. Rich Deem offers a discussion of the age of the earth as determined scientifically and as suggested in Christian-Jewish scriptures.
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