| |
| 4
billion years ago |
Primordial
Earth
Life on Earth began about four billion years ago, when volcanism
spewed forth gases to create a thick atmosphere, and water vapor
clouds condensed to form the oceans. Crashing meteorites and comets
brought organic molecules to the mixture. Electrical storms, volcanism,
and radioactivity provided the energy needed to spark the mixture
to life. |
| 3.8
billion years ago |
Life
Begins to Assemble
In modern cells, RNA follow the genetic plan supplied by the central
strand of DNA. However, DNA, on which all living things store their
genetic information, seems too elaborate a starting point for early
life. It may have relied instead on RNA, which is able to make crude
copies of itself. |
| 3.5
billion years ago |
Cells
Take Form
Nestled in a cavity etched from 3.86-billion-year-old rock, this
tiny ball of carbon may be the oldest evidence of life on Earth.
Many scientists believe that meteorites supplied the early Earth
with amino acids that could have turned into layered structures
similar to cell walls. According to one scenario, these acids accumulated
as foam on the oceans and were carried by wind and waves onto ancient
tidal flats, where they formed into the cell membranes of Earth's
first microorganisms. |
 |
| 3 billion
years ago |
Global
Gas Warfare
Stromatolite reefs still flourish in Shark Bay, Australia, as they
did throughout the globe 3.5 billion years ago. Stromatolites are
made up of different layers of bacteria. The first bacteria thrived
in an oxygen free environment. Then mutant offspring began to produce
oxygen, poisoning the parents. As the air became richer in oxygen,
the offspring took over the surface; burying the parents and creating
the layers that make up the stromatolite. |
 |
| 2
billion years ago |
Triumph
of Oxygen
Sea water once contained dissolved iron. The oxygen produced by
bacteria reacted with the iron, which resulted in rust on the ocean
floor. Millions of years later this rust turned into deep beds of
banded rock. Eventually, all the iron in the oceans was oxidized,
making the atmospheric oxygen levels rise sharply, benefiting larger
organisms. |
| 1.5
billion years ago |
Sex
is Invented
Until now all cells reproduced by self replicating, or creating
identical clones of themselves. Then eukaryotes began to emerge.
New combinations of genes can be assembled in an organism. How
do new genes arise? |
 |
|
BIOL
230 lab contents