• Categories

  • Most Popular Questions

  • Recently Viewed Questions

  • Recent Answers

    How To Make a Digita… on What does a frequency of 100 H…
    Daigrepont on Can an earthquake cause air tu…
    Benedict on How did God come into exi…
    joshua on How does the human body g…
    Ian on How did God come into exi…
  • Recent Questions

  • Blog Stats

    • 2,214,856 hits
  • Visitors since 11-3-08

    counter create hit
  • Terms and Conditions

  • Warning

    We are doing maintenance on this site, so some posts may disappear for a short time. Sorry. Normal service will soon be resumed...
  • Pages

  • March 2008
    M T W T F S S
    « Feb   Apr »
     12
    3456789
    10111213141516
    17181920212223
    24252627282930
    31  
  • Archives

  • Meta

How long would it take to evolve a human being?

How long would it take to evolve a human being, if you can’t answer that when how long is it going to take to get humans into space hotels?
Thanks for letting me ask a Q 🙂
Oliver Bryant from Kent (Age 5-14)

Advertisements

One Response

  1. Earth is estimated to be about 4.5 billion years old, and for much of that history it has been home to life in one weird form or another.

    Indeed, some scientists think life appeared the moment our planet’s environment was stable enough to support it.

    The earliest evidence for life on Earth comes from fossilized mats of cyanobacteria called stromatolites in Australia that are about 3.4 billion years old. Ancient as their origins are, these bacteria (which are still around today) are already biologically complex — they have cell walls protecting their protein-producing DNA, so scientists think life must have begun much earlier, perhaps as early as 3.8 billion years ago.

    But despite knowing approximately when life first appeared on Earth, scientists are still far from answering how it appeared.

    “Many theories of the origin of life have been proposed, but since it’s hard to prove or disprove them, no fully accepted theory exists,” said Diana Northup, a cave biologist at the University of New Mexico.

    The answer to this question would not only fill one of the largest gaps in scientists’ understanding of nature, but also would have important implications for the likelihood of finding life elsewhere in the universe.

    Lots of ideas:
    Today, there are several competing theories for how life arose on Earth. Some question whether life began on Earth at all, asserting instead that it came from a distant world or the heart of a fallen comet or asteroid. Some even say life might have arisen here more than once.

    “There may have been several origins,” said David Deamer, a biochemist at the University of California, Santa Cruz. “We usually make ‘origins’ plural just to indicate that we don’t necessarily claim there was just a single origin, but just an origin that didn’t happen to get blasted by giant [asteroid] impacts.”

    Most scientists agree that life went through a period when RNA was the head-honcho molecule, guiding life through its nascent stages. According to this “RNA World” hypothesis, RNA was the crux molecule for primitive life and only took a backseat when DNA and proteins — which perform their jobs much more efficiently than RNA — developed.

    “A lot of the most clever and most talented people in my field have accepted that the RNA World was not just possible, but probable,” Deamer said.

    RNA is very similar to DNA, and today carries out numerous important functions in each of our cells, including acting as a transitional-molecule between DNA and protein synthesis, and functioning as an on-and-off switch for some genes.

    But the RNA World hypothesis doesn’t explain how RNA itself first arose. Like DNA, RNA is a complex molecule made of repeating units of thousands of smaller molecules called nucleotides that link together in very specific, patterned ways. While there are scientists who think RNA could have arisen spontaneously on early Earth, others say the odds of such a thing happening are astronomical.

    “The appearance of such a molecule, given the way chemistry functions, is incredibly improbable. It would be a once-in-a-universe long shot,” said Robert Shapiro, a chemist at New York University. “To adopt this [view], you have to believe we were incredibly lucky.”

    The anthropic principle
    But “astronomical” is a relative term. In his book, The God Delusion, biologist Richard Dawkins entertains another possibility, inspired by work in astronomy and physics.

    Suppose, Dawkins says, the universe contains a billion billion planets (a conservative estimate, he says), then the chances that life will arise on one of them is not really so remarkable.

    Furthermore, if, as some physicists say, our universe is just one of many, and each universe contained a billion billion planets, then it’s nearly a certainty that life will arise on at least one of them.

    As Dawkins writes, “There may be universes whose skies have no stars: but they also have no inhabitants to notice the lack.”

    Shapiro doesn’t think it’s necessary to invoke multiple universes or life-laden comets crashing into ancient Earth. Instead, he thinks life started with molecules that were smaller and less complex than RNA, which performed simple chemical reactions that eventually led to a self-sustaining system involving the formation of more complex molecules.

    “If you fall back to a simpler theory, the odds aren’t astronomical anymore,” Shapiro told LiveScience.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: