We grow; we reproduce; we think. How did it all begin? Our universe began 10 to 15 billion years ago . The initiating event is described as the big bang.During the first 3 minutes after the big bang, as the universe began to expand, energy density reduced enough to allow protons, neutrons, and electrons to form. Some of the very lightest of the elements also formed, including some helium and lithium. Protons are hydrogen ions, and so can be indicated as p+ or as H+. They are positively charged.
Electrons are negatively charged; neutrons are uncharged. The formation of stars and galaxies began during the first billion years after the big bang. Some continue to form, even today. Other than hydrogen, the elements important for life, such as carbon, nitrogen, and oxygen, were formed in stars by nuclear reactions. These elements then distributed across space as the early stars exploded into supernovas and spread the atoms necessary for life. Since many of the elements necessary for life were generated in stars, we are "stardust." Gravity caused the coming together of such stardust to form the earth. But we also have as part of us hydrogen atoms whose history may date all the way back to minutes after the big bang.
Our solar system, including earth, formed about 4.5 billion years ago. The first life on earth formed about 3.5 to 4 billion years ago. Complex, photosynthesizing organisms were present by 3.5 billion years ago. Members of the genus Homo (human-like ancestors of ours) first walked the earth about 2 to 4 million years ago. (Please notice the thousand-fold shift here, from billions to millions.) Our species, Homo sapiens, first evolved about 200,000 years ago. The latest genetic evidence suggests that Homo sapiens emerged out of Africa about 100,000 years ago, spreading to Asia and Europe, and then to other continents.
We all are related-there probably was but a single origin for all humans.
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Electrons are negatively charged; neutrons are uncharged. The formation of stars and galaxies began during the first billion years after the big bang. Some continue to form, even today. Other than hydrogen, the elements important for life, such as carbon, nitrogen, and oxygen, were formed in stars by nuclear reactions. These elements then distributed across space as the early stars exploded into supernovas and spread the atoms necessary for life. Since many of the elements necessary for life were generated in stars, we are "stardust." Gravity caused the coming together of such stardust to form the earth. But we also have as part of us hydrogen atoms whose history may date all the way back to minutes after the big bang.
Our solar system, including earth, formed about 4.5 billion years ago. The first life on earth formed about 3.5 to 4 billion years ago. Complex, photosynthesizing organisms were present by 3.5 billion years ago. Members of the genus Homo (human-like ancestors of ours) first walked the earth about 2 to 4 million years ago. (Please notice the thousand-fold shift here, from billions to millions.) Our species, Homo sapiens, first evolved about 200,000 years ago. The latest genetic evidence suggests that Homo sapiens emerged out of Africa about 100,000 years ago, spreading to Asia and Europe, and then to other continents.
We all are related-there probably was but a single origin for all humans.
For Question answer Click Here
