Origin of Life on Planet Water - Index
Spontaneous Generation - The Primeval Soup
Panspermia - Life Hitched a Ride to Earth from Space
Evolution Pathway and Links to the Climate and Atmosphere
=>> Evolution of Planet Water
The First Forms of Life
Evolution of Life as We Know It
How Plants Change the Atmosphere
Is There Life Elsewhere ?
The Origin of Life on Planet Water
History of the Universe
|Billions of Years Ago
|| First Multicelluar forms
||Solar System formed
History of Planet Water
The following summary describes important stages in the development of water-carbon-based
life on Earth, beginning with the birth of the Solar System about 4.6 billion years ago.
=> Years 0.0 to 0.1 Billion
Within the first 100 million years of the birth of our solar system, protoplanets
agglomerated from a disk of dust and gas that surrounds the Sun. Not long after,
the protoplanetary Earth was struck by a Mars-sized body to form the
Earth and Moon.
Geologists have determined that the Earth is about 4.56 billion years old.
=> Years 0.1 to 0.8 Billion
Initially, the Earth's surface was mostly molten rock that gradually cooled through
the radiation of heat into space.
The primeval atmosphere was composed mostly of water (H2O), carbon dioxide (CO2) and
monoxide (CO), molecular nitrogen (N2) and hydrogen (H2), helium (He) and hydrogen
chloride (HCl) outgassed from molten rock, with only traces of reactive molecular
The Earth's second atmosphere that developed after the surface cooled, most likely
resembled that of Jupiter's atmosphere. It was formed mostly from the outgassing of
such volatile compounds as water vapor, carbon monoxide, methane, ammonia, nitrogen,
carbon dioxide, nitrogen, hydrochloric acid and sulfur produced by the constant
volcanic eruptions that besieged the Earth.
This atmosphere was rich with water vapour released from hydrated minerals and cometary
As the Earth continued to cool from Years 0.1 to 0.3 billion, the rain that fell on
earth initially turned to steam upon hitting the still hot surface.
But as the surface cooled the rain finally collected into hot or warm seas and
oceans surrounded by the crust that solidified.
Frequently large asteroids or comets struck the planet remelting the crust and
turned oceans back into hot mist.
Eventually, a stable rocky crust may have developed between Years 0.2 and 0.4 billion.
Earth's oldest surviving rocks, from western Greenland's Isua greenstone belt
are estimated to be 3.85 billion years old and contain traces of organic molecules.
This suggests that self-replicating, carbon-based microbial life became well developed
during Earth's first billion years of existence.
Single-celled microbial life lacking a nucleus (prokaryotes) were probably the
first forms of life resembling those of modern times. These microbes metabolized
hydrogen-rich compounds or organic materials to derive the energy that sustains anaerobic
They may have included
- sulfate-reducing bacteria that produce Hydrogen Sulfide (H2S),
- fermentative bacteria that produce carbon dioxide and alcohol (-OH), and
- methanogenic bacteria that produce methane (CH4).
Many of these anaerobic microbes -- particularly the methanogens found in sewage and
mudflats today -- are easily poisoned by oxygen. On the other hand, the recent discovery of
banded sediments with rusted iron on Akilia Island in West Greenland suggests, that
oxygen-producing microbes living on the surface of wet areas to gather Sun light may
have developed by the end of this geologic period (3.85 billion years ago) despite
continuing bombardment from space.
=> Years 0.8 to 2.1 Billion
Reduced cometary and meteoric bombardment allowed anaerobic microbes to spread
widely in wet habitats on land as well as in the oceans.
Life diversified and adapted to new habitat -- some on land -- but stayed
By the end of this period, microbes with the ability to produce oxygen were widespread,
releasing large quantities into the oceans and atmosphere.
Many of these microbes persist today; for example, blue-green (cyanobacteria) or bright
green, photosynthetic bacteria use light from the Sun and chlorophyll to convert carbon
dioxide and water into "free" molecular oxygen and carbon, made into essential organic
substances such as carbohydrates.
Other bacteria use bacteriochlorophyll and other photosynthetic proteins to convert light
to metabolic energy.
Bacteria formed microbial mats on land as early as three billion years ago.
Fossilized remnants and other biochemical evidence from South Africa suggest that
photosynthetic bacteria may have colonized the wet surface of clay-rich soil
during rainy seasons.
=> Years 2.1 to 2.6 Billion
Some of the oxygen produced by photosynthetic bacteria was absorbed (oxidized) by iron
dissolved in Earth's oceans.
This produced an ancient rain of minute, 'rusty' particles to accumulate on the bed
of the ancient ocean floors that is found today as bands of haematite in rock.
As molecular oxygen became abundant, a fraction underwent continuous conversion into a
tri-atomic form known as ozone (O3). The ozone rose to form a layer in Earth's atmosphere
which helps to protect the planet's carbon-based life forms moving onto the land from
damage by the Sun 's ultraviolet radiation.
As photosynthetic bacteria prospered and spread, and higher forms (the 'eukaryotes')
developed, the concentration of oxygen in air and water became abundant.
Free oxygen began to build up around the middle of the Proterozoic Period -- around
1.8 billion years ago -- and made way for the emergence of life as we know it today.
This event created conditions that were toxic for most organisms present and
thus made way for the more oxygen dependent life forms to flourish and take over.
This heralded the start of the Cambrian Period began, about 550 million years ago.
During this period, life "exploded," developing almost all of the major groups of
plants and animals in a relatively short time.
Anaerobic microbes in many habitats died out in massive numbers. Earth's primeval
atmosphere was also rich in carbon dioxide, perhaps 100 times as rich as today.
The success of photosynthetic microbes eventually depleted carbon dioxide
levels to such an extent that the greenhouse effect became negligible around
Year 1.5 Billion.
Around this time, some anaerobes mutated to become "aerobic" purple bacteria
(proteobacteria) that metabolize molecular oxygen and substances produced by life such
as carbohydrates into carbon dioxide and water.
Many microbes eventually merged into symbiosis with other microbial types by ingestion
About two billion years ago, some of these protists merged with oxygen-breathing
purple bacteria, which became mitochondria inside them. Subsequently, some of these
aerobic protists merged with photosynthetic bacteria, which became chloroplasts and
other plastids, to create free-swimming green algae and the precursors of today's
As a result, these new microbes -- called protoctists in the Serial Endosymbiosis Theory
(SET) of Lynn Margulis -- became quick adapters to new environments and expanded greatly
in diversity as well as numbers.
=> Years 2.6 to 3.6 Billion
The first multi-cellular life forms (e.g., fungi, plants, and many plant- and
animal-like protoctists) evolved. Multi-cellularity, of course, allowed fungi and plants
to grow larger than their microbial ancestors.
With the exception of the larger true Algae (seaweeds and kelp), however, most
protoctists that persisted to modern times have remained microscopic in size.
=> Years 3.6 to 4.1 Billion
Earth may have entered a cycle of "Snowball" to "Acidic Hothouse" swings between Years
3.85 and 4.02 billion.
This may have occurred because the continents were clustered around the equator, and so
a warm Earth would be much more vulnerable to slight cooling trends that trigger a
Again, after a massive extinction, intense evolutionary pressure through genetic
isolation and selective adaptation may have resulted in a burst of multi-cellular
evolution and diversity, leading to the first multi-cellular "animals."
The first forms were "invertebrates", lacking a backbone. This included worms,
molluscs, and arthropods (joint-footed animals), invertebrates are among the most
successful animals today.
=> Years 4.1 to 4.6 Billion
After over three billion years of evolution, multi-cellular life -- beginning with
green algae, fungi, and plants (mosses, ferns, then vascular and flowering plants)
began adapting to land habitats. This was done by carrying a 'sea-like' fluid
within them in which the cells were bathed as blood and body fluids.
Exploiting land habitats new symbiotic relationships were formed to contain and
move water. This included the fusion of some fungi and algae to create lichens -
communities with bacteria that survive extreme desiccation on land while breaking
down rock into soil. Associations were also formed between mycorrhizae fungi and
the root tissue of new vascular plants -- culminating in trees that pump water high into
the air -- to exchange mineral nutrients (e.g., phosphorus) and usable "fixed" nitrogen
from the atmosphere for photosynthetic products.
More advanced animal forms followed, such as insects and animals with
backbones known as "vertebrates" (which include the Fishes, Amphibians, Reptiles,
Dinosaurs, Birds, and Mammals).
As a result, the biomass of life on land has become hundreds to thousands of times
greater than that of life in the seas.
The history of life on Earth has been marked by a series of mass extinction events.
(See: Evolution of Life as we know it
The extinction of the Dinosaurs, 500 million years may have been caused by a
large asteroid or cometary impact about 65 million years ago centered near Puerto
Chicxulub, at the tip of Mexico's Yucatan Peninsula.
As happened many times the lost of one group paved the way for another. The demise of
the Dinosaurs created ecological conditions, which eventually fostered
the development of modern Humans (as Homo sapiens ) only about 50,000 years ago.
Bacteria still remain the Earth's most successful form of life - found everywhere from
miles deep below as well as in surface rock, within and below the oceans and polar ice,
floating in the air, and in Homo sapiens and other species.
Planetary Impact of Life
All the millions of life forms on Earth seek energy and food while generating waste heat
Consequently, massive amounts of reactive gases such as oxygen, hydrogen, and methane are
continually being added to Earth's now "anomalous" atmosphere faster than they would
otherwise be removed by inorganic chemical processes.
Paradoxically, despite Our Sun becoming perhaps a third brighter over the past four
billion years since life developed on Earth, geologic evidence suggests that the planet has
become cooler through life-induced reductions in the amount of greenhouse gases in
There is still conjecture about the extent to which non-intelligent life on Earth is
able to adjust planetary conditions to promote its continued survival and, indeed,
prosperity -- debate between a weak and a strong "Gaia" hypothesis.
What is known is that life, the atmosphere and the climate are closely intertwined with
fluid water as the key aspect.
It remains to be seen whether the Human species which has been on the planet for
100,000 years can survive as prosper without causing a catastrophe with this balance,
and so causing its demise. If you consider the period of life of this planet as a
calendar year, humans have only been here for the last 10 minutes !!
>> Next See The First Forms of Life >>