Cells and Molecules - Brutes or Angels: Human Possibility in the Age of Biotechnology - page 24

here we briefly consider some aspects of life's antiquity and origins upon
which virtually all biologists agree. information about natural selection's
creativity helps to give scientific and ethical perspective to humankind's in-
creasing power over its own future evolution via embryo selection (chap-
ter 3) and genetic enhancements (chapter 6) and to the human design and
creation life (chapter 10).
first, consider the origin of the elemental building blocks for life: car-
bon (C), oxygen (o), nitrogen (n), hydrogen (h), sulfur (s), phosphorus
(P), iron (fe), and several trace elements. These and all other elements
found on earth were forged in the core of a massive, collapsing star in our
galactic neighborhood during the final stages of its life. spewed out into
space when the dying star exploded as a super nova, this elemental stardust
is the substance that formed the planets and other bodies that coalesced
to create our solar system about five billion years ago. since all of the ele-
ments in living cells come from the planet earth, we and all other living
things in the biosphere are stardust, literally. What a wonderful thing for
us all to have in common.
it took about 1 billion years for prokaryotic (bacterial) life to emerge
on the surface of the new earth. Thinly sliced rocks dated 3.5 to 3.8 bil-
lion years old and examined microscopically contain fossilized remains of
prokaryotic cells. These cells were non-photosynthetic. Photosynthesis re-
leases oxygen (o 2 ) into the atmosphere, and geological evidence shows that
oxygen did not start accumulating in the atmosphere until about 2.4 bil-
lion years ago.
exactly when eukaryotic cells first appeared on earth is controversial.
fossil evidence for cells containing a membrane-bound nucleus, the hall-
mark of eukaryotic cells, is present in rocks about 2 billion years old. But
from other evidence, most biologists believe that the eukaryotic lineage is
older than that, perhaps as ancient as 3 billion years. 17 Although prokary-
otic cells sometimes grow in colonies, true multicellular organisms are all
eukaryotic. fossil evidence for the oldest known multicellular organisms
appears in rocks 2.1 billion years old (Donoghue and Antcliffe 2010; el
Alani et al. 2010).