Origins

Life is tenacious, and it completely permeates the surface layer of the planet. We find life beneath the deepest ocean, on the highest mountain, in the driest desert and the coldest glacier, and deep down in the crustal rocks and sediments.

Not knowing what conditions are needed for the emergence of life, it is only possible to speculate about its existence elsewhere in the universe...

IN THE BEGINNING...

The Earth began as a twinkle in the Solar Nebula's eye some 4.5 billion years ago and it - along with the rest of the planets, asteroids, meteors, comets - formed, it is thought, through the tendency of matter to clump together, ever more until finally there were substantial bodies, the planets and their moons, sweeping up all left-overs in their orbits. During this era, approximately one billion years long, the newly-borning Earth was pummeled mercilessly by these left-overs. This was the so-called "Hadean Period" (and well named at that!), a "hell-ish" time indeed when the Earth's surface was periodically broiled, flash-fried so to speak. Incoming asteroids of sufficient size would actually vaporize, themselves and the part of the surface they impacted and this would turn into a seering plasma that would tsusami around the globe - not a pretty picture. Not to mention volcanic eruptions.

This made it a little hard, one would think, for life to get a toehold on the young planet's surface.

How close are scientists to knowing the origin of life on earth?

When did eukaryotic cells (cells with nuclei and other internal organelles) first evolve?

The Origins and Early Evolution of LIfe
-- The Department of Chemistry and Biochemistry. UC Santa Cruz

The Precambrian
Outline
-- Georgia Perimeter College, Geology 102

THE ORIGIN AND EARLY HISTORY OF LIFE INTRODUCTION
Outlines & Key terms Page:
-- Northern Arizona University

BIO 106 Evolution & Ecology
-- University of Cincinnati

"An equally interesting question that is currently studied in laboratories on Earth is how life originally could have arisen from lifeless molecules, and evolved into the already sophisticated isotope fractioning life forms ... [in such a short period of time]...."
from Life on Earth began at least 3.85B years ago

Early Fossil Gallery
-- Museum of Natural History, Tohoku University, Sendai, Japan

Making Organic Compounds: The Stanley Miller Experiment & Others

Although the primitive atmosphere is no longer believed to be as rich in hydrogen as once thought, the discovery that the Murchison meteorite contains the same amino acids obtained by Miller, and even in the same relative proportions, suggests strongly that his results are relevant.The Beginnings of Life on Earth

Others have made similar experiments. A group at the Department of Chemistry and Biochemistry at the University of California, San Diego, exposed sulfur-bearing molecules like those thought to have been present before the Earth formed to low levels of light. The presence of the light was enough to generate organic compounds - molecules containing carbon, which form the chemical basis of life as we know it. Meteorite Reveals Life Not Difficult to Make

The new compounds had a distinct isotopic (atomic makeup) signature, not normally found on Earth. In fact, the peculiar part is that these isotopes have only been found one other time, in compounds removed from the Murchison meteorite.

Outline for Prebiotic Chemistry Teaching Module
-- Exobiology for High School Students, La Jolla High School

LINKS

Macromolecules

from Concepts Of Biology Lecture Topics
-- College of St. Elizabeth, N.J.

Biology Glossary
"alphabetized lists of biological terms mostly from the areas of molecular and cellular biology"
-- Private website

The Evolution and Organization of the Cell
-- Ohio University

RNA Stuff
Why is modern metabolism dominated by protein enzymes? There is a "chicken-and-egg" paradox of how to initiate theflow of genetic information at life's origin, since proteins encoded by DNA are required for the replication of DNA. To circumvent this dilemma, Francis Crick and others proposed thirty years ago that primitive forms of life contained RNA as their sole genetic and catalytic molecules (the "RNA World"). The discovery of natural catalytic RNAs renewed vigorous speculation over the role of RNA in early evolution, most of it going well beyond the reach of supporting data. Through in vitro selection technologies, we can now test RNA World hypotheses through direct experimentation.

from RNA catalysis, Origin of Life, & metabolic engineering
-- Private Website

The RNA World: History of an idea, an idea of history
-- Private Website

Origins of Life and the RNA World: Never Underestimate the Power of Soup
-- Private Website

The RNA World: A Critique
-- Access Research Network

Insight into Self-Replicating RNA
"It may help researchers trace the origins of life, as the ever-recurring argument of which came first - the informational molecule (nucleic acid) or the catalyst (protein enzyme) comes closer to having its answer."
-- NanoNews, 10/30/96

Yale Scientists Recreate Molecular Fossils," Now Extinct, That May Have Existed At The Beginning Of Life
"...report they have synthesized molecules like those that probably gave rise to the earliest life forms on Earth nearly 4 billion years ago..."
-- ScienceDaily, 6/10/98

Primitive Protease Discovery May Unlock Mysteries Of Enzyme Evolution
"a primitive protease (an enzyme that cleaves proteins), that may hold the key to a better understanding of how enzymes evolved. Enzymes, which are protein catalysts, are critical to every physiological function within the body. Without them, even the most basic biological functions would occur so slowly that our bodies would simply shut down."
-- P\S\L Consulting Group Inc, 1998

First Organisms

• it would have been anaerobic
• it would have been hyperthermophilic and halophilic
• it would have been a chemolithoautotroph, obtaining both energy and carbon from inorganic sources, using H2 or reduced sulfur compounds as electron donors and CO2 or oxidized sulfur as electron acceptors to provide energy and fixing CO2 as their carbon source.

(Chemolithoheterotrophs would have evolved later in this scenario as "opportunistic" consumers of organic matter formed by autotrophic producers. There is also a hypothesis that the first living organism was heterotrophic but this could only have been true if the prebrotic broth contained significant concentrations of abiotically produced organic molecules, which is not likely, especially from the point of view of continuous supply.)

Modern chemolithoautotrophs
Organisms thought to be similar to these first chemolithoautotrophs have been isolated in the last few years from what we would call "extreme environments". These organisms are isolated from hot sulfur springs on the earth's surface or hydrothermal vents ("black smokers") on the ocean floor where these organisms form purely prokaryotic ecosystems.

Conditions in these environments are thought to mimic those present on the early earth, i.e. high temperature, high ulfur, anaerobic, high salt.

These organisms grow optimally under anaerobic conditions in high salt at 80-110 C, in fact they grow completely independent of oxygen and sunlight; they could even grow on another planet if water was available.

They may be relatively unchanged genetically and structurally from the first living cells. This is borne out by sequence analysis of 16S rRNA genes and other genes which are highly conserved during evolution (i.e. ancestral genes).

from What were the first living organisms like?
-- Department of Biological Sciences, University of Alberta

Cells existing prior to 1.5 billion years ago were all prokaryotes, such as bacteria. Eukaryotes appeared about 1.5 billion years ago.

Prokaryotic Cells
Cells of the most primitive organisms have cells that lack a nucleus.
Monerans (bacteria and related organisms) are prokaryotes.
Prokaryotes also lack other membrane-bound internal structures.

Eukaryotic Cells
All organisms, other than monerans, have cells with nuclei.
Cells with nuclei = eukaryotic cells, and the organisms made of such cells are eukaryotes.
Eukaryoyic cells have membrane-bound internal structures (organelles) in addition to the nucleus.

from The Evolution and Organization of the Cell
-- Ohio University

Earliest Evidence of Life

We are looking at some two to three hundred million years for the appearance of a form of life on Earth.

Evolutionary/Geological Timeline

Studies of early Earth environments and the evolution of microbial life
"... provide a background for understanding present life and environments. Many different research techniques address questions of early life under the guises of chemistry, biology, and geology. While chemical and biological studies provide clues to possible processes that may have been involved and the relationships among extant life, geology provides a historical record of the processes that actually operated on the ancient Earth and lead to our current Earth. Much of my work has focused on unraveling clues to early life and environments preserved in 2.5 billion year old rocks from South Africa."
-- Caltech, Division of Geological and Planetary Sciences

LINKS

Stromatolites

from Early Life on Earth: Stromatolites
Images
-- Worldwide Museum of Natural History

Archean Microbialites
Technical paper
-- Caltech, Division of Geological and Planetary Sciences

Stromatolite-Thrombolite Associations
Technical paper (w/ images)
--University of Göttingen

Travertine and stromatolites
Technical paper w/ good description of stromatolite varieties and formation
-- Paleolimnology & Diatom, Biology Department, Indiana University

Paleolimnology & Diatom Home Pages
-- Biology Department, Indiana University

Hamelin Pool Marine Nature Reserve
"Hamelin Pool is one of only two places in the world with living marine stromatolites, or 'living fossils'. Stromatolites are able to survive in the area because Hamelin Pool's water is twice as saline as normal sea water and seagrasses and many other forms of life cannot survive there. ... They look like rocky lumps strewn around the beach but are actually built by living organisms too small for the human eye to see."
-- Department of Conservation and Land Management, Western Australia

The Earliest Life
"The oldest fossils are approximately 3.5 Billion-year-old stromatolites. These are colonies of cyanobacteria (formerly called blue-green algae) which built real reefs..." (links)
-- Paleobotanical Research Group, University of Muenster, Germany

Geology Resources for Other "Giant Fossil" Structures

Reefs
Geological History of Gray's Reef National Marine Sanctuary

Limestones

• Chalk - soft, friable, porous; micro-fossils
  coccoliths, 1-celled plants
  foraminifera, 1-celled animals

• Oolites - composed of sand-sized spheres - ooids (like limestone “snowballs”)

• Stromatolites and Reefs
  
  • Stromatolite - formed by trapping of sediment by algae; some of the earliest fossils
    
  • Reefs - biogenic buildup; carbonate secreting organisms; marine atoll - circular chain of coral islands

from Geo101
-- Texas A&M University

Recent Evidence for Earliest Multicellular Life

The term "triploblastic" refers to animals whose body parts are organized into layers that are derived from three tissue layers in the embryo.
PAE Glossary

The most primitive of these existing now are the flatworms or Platyhelminthes. Flatworms form one end of the "coelomate" (animals with internal cavity) continuum - which includes mammals.

LINKS

Murchison Meteorite & Extraterrestrial Organic Compounds

Indeed, analysis of Comet Hyatuke has shown a very similar chemical makeup between it and Murchison. Chemical Measurements of Comet Hyakutake Suggest a New Class of Comets

An abundance of amino acids found within this meteorite has led to intense study as to its origins. More than 92 different amino acids have been identified within the Murchison meteorite to date. Nineteen of these are found on Earth. The remaining amino acids have no apparent terrestrial source.

The fact that various simulation experiments (see above) have produced results consistent with chemistry found in the Murchison meteorite has led to the idea that these compounds, which are generally associated with the chemistry of life, were perhaps available in the makeup of the primitive solar nebula and therefore did require any special circumstances for their appearance on Earth.

LINKS

Tholins & Other Organic Chemistry in Space

Abiotic Chemistry

Simulation experiments and the ideas swirling around the discovery of organic compounds extraterrestrially have fueled the new chemical discipline of "abiotic chemistry." Besides amino acids and other organic acids, experiments in abiotic chemistry have yielded sugars, as well as purine and pyrimidine bases, some of which are components of the nucleic acids DNA and RNA, and other biologically significant substances.

It seems very likely that these small organic molecules, that are now known to form readily in the laboratory and appear to occur naturally extraterrestrially - that these are the first building blocks of life. To what extent these substances arose on earth or were brought in by the falling comets and asteroids that contributed to the final accretion of our planet is still being debated.

LINKS

The Case for Seeding from Extraterrestrial Sources

One. We know that meteors infallen on Earth have come from other planets in the Solar System, in particular from Mars. How can we know this? We actually can - ever since the Viking Lander missions to Mars, we know precisely what the makeup of the Martian atmosphere is - it has a specific "fingerprint" that identifies these meteors beyond a trace of doubt. How could a meteor from Mars get here? Well, a pretty good-sized asteroid crashing into Mars at, say, an oblique angle, would hurl surface material at escape velocities off-planet. We can reasonably assume that the planets have traded rock. Could microbial life have hitch-hiked from one planet to another?

Two. Consider this. We can calculate that four billion years ago the sun was almost half as hot as it is today. It seems likely that Earth and, say, Mars, were frozen during this time. On the other hand, Venus may have been sitting pretty and perhaps had warm liquid oceans. This is pretty speculative but perhaps life evolved there and spread by the mechanism just detailed to Earth (and Mars?). Some suggest that perhaps life is endemic to the universe: note the presence of complex carbon compounds in interstellar space and on comets and meteors.

The Panspermia Hypothesis goes a step further and suggests that life is basically a property of the universe and it will be found in all possible habitats as a matter of course.ref

But - we are still left with the question: how and under what circumstances does life start?

LINKS

Extreme Environment Origin Hypothesis

And yet, apparently within a short 300 million years after the last asteroid par-boiled the Earth's surface, life had evolved. Or otherwise 'occurred.'

This has led some to suggest that life developed not on the surface at all, but below the surface, perhaps in a super-heated environment like that which we find at the oceanic ridge 'smokers.'

Part of the reasoning behind this is the primitive nature of the hyperthermophilic Archaea lifeforms that have been discovered only in the last fifteen years.

LINKS

Origin of Life Research
"Since the discovery of submarine hotsprings along mid-ocean ridges, many scientists have believed that life on Earth could have originated where hot volcanic waters well up and mingle with the sea. UK earth scientists Professor Mike Russell and Dr. Allan Hall of Glasgow University now think they have discovered a natural chemical mechanism for how this might have happened."

Origin of Life Research Index
-- University of Glasgow

Evidence for a common origin for Life on Earth

• DNA and RNA are apparantly the 'universal' basis for all life on Earth.
• Only 20 [known] amino acids are used in all living things on Earth. L-amino acids exclusively are used in all living things on Earth.
• ATP* is the 'universal' energy used in all living cells.
• Fermentation is the first step in ALL metabolism.
• Highly efficient oxygen-burning represents a 'last' step in aerobic organisms.

LINKS

General Links