![](https://webarchive.library.unt.edu/eot2008/20090826004938im_/http://astrobiology.nasa.gov/img/_placehold/placehold-ask.jpg)
![Ask an Astrobiologist](https://webarchive.library.unt.edu/eot2008/20090826004938im_/http://astrobiology.nasa.gov/img/text/ask-an-astrobiologist.gif)
"I don't understand the purpose of Area 51. Could you tell me? Also, could you explain if Area 51 has found forms of life from other planets?"
Special Note
Ask an Astrobiologist has received nearly a thousand questions about Nibiru and 2012, with more than 200 answers posted. Please read a summary of the answers that have already been posted, use the search feature and read the FAQ’s before submitting questions on these topics.
-
Question
How long have humans existed on Earth?
Human have existed for roughly half a million years, but this answer depends on the exact definition of "human". Fossil evidence shows that several human-like lineages developed during the past million years or so. >From fossils, the appearance of Homo sapiens is dated at about half a million years, and of anatomically modern Homo sapiens at about a hundred thousand years, values that are also supported by genomic evidence. Another data point, although not something you asked directly, is that the recent complete sequencing of the genome of the chimpanzee, which is the closest living relative of humans, suggests that chimps and humans diverged from their common ancestor about 6 million years ago. Of the many intermediate related species that have existed since then, only chimps and modern humans survive today. David Morrison
NAI Senior Scientist
June 12, 2006
![FAQ](https://webarchive.library.unt.edu/eot2008/20090826004938im_/http://astrobiology.nasa.gov/img/text/hd_faq.gif)
- How frequently are questions answered?
- I asked a question but there was no answer?
- Who is the Astrobiologist answering these questions?
- Will I get an email when my question is answered?
- What college courses should I take to become an astrobiologist?
- How can I get a job as an astrobiologist at NASA?
- Have aliens visited Earth? Are UFOs real?
- Is there a planet or brown dwarf called Nibiru or Eris that is approaching the Earth and threatening our planet with widespread destruction?
- Is it true that the Sun will be in the center of the Milky Way Galaxy in December 2012 and that this will cause a pole shift and massive destruction.
- Has NASA discovered life on other worlds?
- Astrobiology Career Path Suggestions