Skip to main content

View Diary: A Perspective on Life on Earth (74 comments)

Comment Preferences

  •  Timing quibbles (0+ / 0-)

    The presolar nebula was not necessarily made of material from exploded stars. The molecular cloud certainly included such elements, but the predominantly hydrogen cloud is unlikely to have been the remains of a star, as hydrogen is the primary fuel of a star. Rather the heavy elements came from the explosion of a nearby supernova, which is what caused the cloud to collapse.

    Life may have had a foothold sooner than 3.5 billion years ago. The Late Heavy Bombardment ended 3.9 billion years ago, and rock formation from immediately following that time period show some indications of biological chemistry.

    There were no chordates 500 million years ago.

    The dinosaurs did not go extinct 65 million years ago - they are not extinct even now. Only non-avian dinosaurs did.

    The Hominidae originated 14 million years ago, and not 7 million - unless by that you mean human ancestors. Those came about not more than about 6 million years ago, as DNA evidence suggests human-chimp divergence only began then, and did not complete for another million and a half years (see Ardipithecus.)

    Rick Perry - the greatest scientist since Galileo!

    by Bobs Telecaster on Fri Nov 30, 2012 at 06:56:13 AM PST

    •  Why quibble? (0+ / 0-)

      The presolar nebula had to have material from exploded star, otherwise, there would be no heavy elements. Which you seem to understand, but contradict anyway?

      There are many chordates in that time frame. Just one example. "Myllokunmingia is a chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate,[1] although this is not conclusively proven.[2] It is 28 mm long and 6 mm high.

      It is among the oldest possible craniates, found in the lower Cambrian Chengjiang (524 million years ago). It appears to have a skull and skeletal structures made of cartilage. There is no sign of mineralization of the skeletal elements (biomineralization)."

      Perhaps saying backBONE was too specific. SPines might have been better.

      Avians are not dinosaurs. Avians evolved from dinosaurs. They had started diverging a hundred million years before the extinction of the dinosaurs.

      Technically, Homidae may have diverged as early as 20 million years ago. Trying to keep it human.

      Nearly all of this stuff has various theories and disagreements and proponents of those. I made this the generally accepted argument. Like all things science, it is subject to change with better data.

      •  Aves are dinosaurs (0+ / 0-)

        No modern cladist disputes this. Most theropod dinosaurs of moderate size or less, if they wandered into a zoo today, would probably be called birds, and would look like them... as they were covered with feathers.

        The Avialae clade (to which class Aves belong) is definitely a subclade of the Dinosauria.

        Rick Perry - the greatest scientist since Galileo!

        by Bobs Telecaster on Sat Dec 01, 2012 at 12:05:57 PM PST

        [ Parent ]

Subscribe or Donate to support Daily Kos.

Click here for the mobile view of the site