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 Key Stage
1 BYA First Multicelluar forms
2 BYA Oxygen Appears
4 BYA Earliest Life
5 BYA Solar System formed
10 BYA
11 BYA
12 BYA

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 oxygen (O2).

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 impacts.

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 life.

They may have included
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 single-celled.

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 without digestion.

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 plant cells.

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 Snowball period.

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 and materials.

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 the atmosphere.

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 !!

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