Page 8 - DINOSOUR ATLAS

Dinosaur atlas
Life on Earth

The gianT repTiles of The dinosaur age were among the most spectacular
products of evolution, the process that has formed all living things.
The process began in the sea over 3,500 million years ago, when a
number of chemicals became linked together in a complex compound
that was able to make copies of itself. In other words, it became alive.
The chances of this happening are so slim that it may have occurred just
once in the history of the universe. Yet it did happen and, once a living
organism existed, it was able to multiply, evolve, and give rise to the
wonderful diversity of life on Earth.

spark of life .
All life is based on deoxyribonucleic
acid, or DNA (an extremely complex
substance that controls growth and
reproduction). For life to begin, DNA—
or something like it—must have been
created from a series of reactions
between simple ingredients like the
nitrogen, methane, sulfide, and water
vapor that formed part of the early
atmosphere. The energy needed to
trigger the reactions could have been
provided by lightning—the original
spark of life.

, liVinG Cells
The first living things probably resembled
bacteria, the simplest organisms found on Earth
today. Each bacterium is a microscopic sachet
of fluid containing sugars, fats, proteins, and
DNA, enclosed within a cell membrane. It can
feed, grow, and replicate itself. Over millions of
years, similar cells developed ways of working
together to build the complex multicellular
organisms that evolved into plants and animals.

These Two bacTeria are among
the simplest of all life forms, but
they are far more complicated
than any nonliving things

Distant anCestors .
The earliest traces of life have been found in Australia,
in rocks that are 3,500 million years old. They are the
fossilized remains of stromatolites—colonies of single-
celled cyanobacteria. These are bacteria that make food
from water and carbon dioxide by photosynthesis,
just as green plants do. They were the only form
of life on Earth for nearly 3 billion years, and
the ancestors of all other living things.

sTromaToliTes still thrive in
Shark Bay, Western Australia,
creating a scene that could have
existed 3 billion years ago