GNN Home. Genome sequencing is figuring out the order of DNA nucleotides, or bases, in a genomethe order of As, Cs, Gs, and Ts that make up an organism's DNA.The human genome is made up of over 3 billion of these genetic letters.hen you read a sentence, the meaning is not just in the sequence of the letters. It is also in the words those letters make and in the grammar of the language. Similarly, the human genome is more than just its sequence.
This blog entry thus provides a basic overview of the four Geologic Eras. The Precambrian Era (4.6 billion years ago to 600 million years ago) encompasses the great majority of Earth's geologic history, stretching from the formation of our planet to the appearance of shelled marine life.
Precambrian time covers the vast bulk of the Earth's history, starting with the planet's creation about 4.5 billion years ago and ending with the emergence of complex, multicelled life-forms almost four billion years later.ome three billion years ago the Earth's atmosphere was virtually devoid of oxygen. At about 2.4 billion years ago, oxygen was released from the seas as a byproduct of photosynthesis by cyanobacteria. Levels of the gas gradually climbed, reaching about one percent around two billion years ago.