The skeleton of the fossilised, 3.2 million-year-old human ancestor known as Lucy, will go on display in the US, Ethiopian officials say.

After four years of negotiations with the Houston Museum of Natural Science in Texas, Ethiopia agreed to lend the bones for scientific study until 2013.

The exact moment when a 550 million year old cell began to divide has been captured in an exquisite 3-D image.

The picture is one of a series taken by researchers examining ancient fossil embryos from Guizhou Province, China.

The specimens, described in the journal Science, are the oldest known examples of fossil embryos, and shed light on the early evolution of complex life.

A dinosaur-era Davy Jones's locker of large, predatory sea reptiles—including a giant that scientists have nicknamed "the Monster"—has been discovered by fossil hunters on an Arctic island.

The ancient graveyard once lay deep underwater during the Jurassic period, about 200 million to 145 million years ago (take a virtual swim with Jurassic sea monsters).

Over the last century, many spectacular discoveries have shed light on the history of the human family. Somewhere between 12 and 19 different species of early humans are recognised, though palaeoanthropologists bitterly dispute how they are related. Famous fossils include the remarkably complete "Lucy", dug up in Ethiopia in 1974, and the astonishing "hobbit" species, Homo floresiensis, found on an Indonesian island in 2004.

Palaeontologists have discovered a bizarre whale fossil in Australia with a set of fearsome teeth.

The specimen has surprised scientists because it belongs to the group known as baleen whales.

Modern day baleen whales are all placid, plankton eaters, but the new fossil shows the group were not always the ocean's gentle giants.

The researchers analyzed specimens from four North American tyrannosaur species: Albertosaurus sarcophagus, Tyrannosaurus rex, Gorgosaurus libratus, and Daspletosaurus torosus.

Using a technique pioneered by Erickson and others, the team counted growth rings

Meant as an introductory text on the concept of fossils and their importance in the formulation of evolutionary theories, this article will discuss the two main types of fossils found in the world today. It will also shed some light on some of the most common questions regarding fossils.

This article serves as the fourth installment of my series on the Theory of Evolution, of which the three first articles were:

• What is Evolution ?: A scientific definition of the concept of Evolution
• The Birth of Intelligent Design: A discussion of the pre-1800 thoughts and theories
• Formulating a theory for Evolution: A 19th century Struggle.: A discussion of the theories surrounding evolution in the 19th Century.

The word Fossil comes from the Latin fossus, literally "having been dug up", and was first used by a German physician, Georgius Agricola, in 1546, to describe a wide variety of minerals, stones, and archaeological as well as paleontological objects. Before Nichola Steno's 1666 revolutionary suggestion that fossils origin were from living organisms, people did not put much importance into fossils, except, maybe, for the fact that they were pretty and neat looking things. Nowadays, the science that studies fossils is called Paleontology, and is closely related to the science of evolutionary biology in the formulation, and validation, of evolutionary theories. As a future references, I will give the Oxford dictionary definition of fossils:

Fossils:

the remains or impression of a prehistoric plant or animal, usually petrified while embedded in rock, amber, etc. -- Oxford Dictionary

Today, when the word fossil is thrown in the air, we often think of the tiny imprint of a 300 000 years old plant, or of a mosquito stuck in tree resin, or even of the bones of a T-rex undug from the our very own grounds in Canada. But how are those fossils really formed ? And how old can this fossil be ? Or, of course, the creationist's favorite, why do we constantly find relatively young fossils and why are there missing links ? These are the type of questions we will look at and hopefully suggest reasonable answers to.

1. How are fossils preserved

In order for a fossil to form, the dead organism must quickly be preserved, which means that it must not be in contact with any agents of decay, such as oxygen, bacteria, radiation, and erosion. This alone explains why most fossils are found in rock or amber, and why they are relatively young (We will come to that in a little while). Thus, in order to be preserved, the dead organism must find itself in mud, which will later dries and becomes rock, or in tree resin, which eventually becomes amber.

The soil in which fossils can be found are therefore very special and are not very common. The main areas where fossils are found today form a pretty short (although increasing) list: Burgess Shale (Canada), Chengjiang (China), Liaoning Province (China), Bundenbach (Germany), Solnhofen Limestone (Germany), and a couple more sites.

You said Amber ?

As I mentioned earlier, tree resin, with time, becomes hard and is transformed in what we call Amber, which is simply a popular name for fossilized resin of botanical origin. It's molecular constituency is mainly carbon and hydrogen atoms that forms rings, which, over time, becomes hard and form this sort of hard gel (See picture). The bubbles formed in the amber fossils are due to other life captured such as bacteria and fungi (See picture).

The most common inclusions in Amber are usually invertebrates, although in rare some cases, tiny vertebrates such as lizards are seen. Fossil resin inclusions are predominately insects, which should be no surprise since botanical resin is an evolutionary adaptation of plants that is, in part, for protection against insects.

What about mud ?

As we mentioned earlier, for an organism to be well preserved, an oxygen-free environment is needed, which unfortunately are pretty much only present underwater. Therefore, the vast majority of the well preserved, and therefore interesting, fossils are found in rock that was once underwater. This means that most of the fossils are underwater animals, or seabirds. This explains the wealth of information on underwater animals that were alive millions of year ago, but does not account for the lack of very old fossils.

The small amount of very old fossils is explained by one of the agents of decay, the so-called erosion. This is probably one of the Paleontologists worst enemy (Seeing as oxygen is very much needed in order to survive...). The main problem is in the fact that erosion, over a long period of time, will destroy rocks, taking the fossils that are in it along with it. Thus, leaving the Earth with a relatively young crust on top. Of course, digging deeper could potentially solve this problem, but is much more expensive.

2. Dating fossils

We have so far explained why fossils are relatively young, and introduced the two main types of fossils found. But how do they date those fossils ? How can they predict that such a fossils was an animal around 4.3 million years ago, or in the case of the mosquito in the picture, about 2 million years ago ?

Relative Dating

Charles Lyell (1797 – 1875), close friend of Charles Darwin, was the scientist who first introduce the idea that recent strata could be categorised according to the number and proportion of marine shells encased within. Based on this he proposed dividing the Tertiary period into three parts, which he named the Pliocene, Miocene, and Eocene. Nowadays, this concept is used to date fossils, in a technique that is called relative dating.

Relative dating consist of dating the fossil based on the strata it was found in. Obviously, this methods has its drawbacks, since it is based on the age of the different strata and the age of what are called index fossils. They are fossils that are commonly found and have a known age (or at least range of age), for example trilobites (See picture). Thus, the dating performed using this methods are usually very quick (for a paleontologist), but fairly inaccurate and vague.

Radiometric Dating

The "more scientific" (at least commonly known) technique for dating fossils is called Radiometric Dating, which consists of calculating the ratio of naturally occurring radioactive isotopes found in igneous rocks (Note its biggest drawback - only specific type of rock can be aged this way). One of the specific methods, called Carbon Dating, is based on the half-life of Carbon-14, which is known to be 5,730 years. Obviously, because of the relatively short half-life, using this method will only enable scientist to date fossils (or objects in some cases) that are less than 60 000 years old (at which point there is a little less than 1/1024 left of the carbon isotopes). To date older fossils, the common method used is called Potassium-Argon Dating, since the half-life of Potassium 40 is 1.25 billion years.

These techniques are much more common and will enable scientist to date bones and rocks in which fossils are found. Note that the fossils themselves are never dated, it is the rock in which the fossil is found that is dated (the fossils are rocks anyways). This gives the paleontologist an idea of the age of the fossil, but not necessarily the exact age. This is why we are often presented a range of age as opposed to an exact date.

3. Conclusions

Although the fossil record plays a very important part in the formulation and the validation of the theory of evolution, it does not completely explains it. In fact, the lack of fossil evidence has often been one of the major arguments against evolution by creationists. Even in the time of Darwin, the fossil record was often used as a proof against evolution, and in a now very popular quote by Darwin's friend, Lyell argues that "the fossil record is like a book of which very few pages are preserved, and of the pages that are preserved, very few lines, of the lines that are preserved, few words, and of the words, few letters". Lyell was also openly in agreement with Darwin's theory, but did not believe in the process of natural selection. The fossil record simply did not support the theory.

To this day, even with a surprising wealth of fossil found (The first dinosaur fossils were only found 20 years ago), some scientist believe in a very different story than natural selection: Punctuated Equilibrium. One of its founders, Stephen Jay Gould (1941 – 2002), explains why:

"The absence of fossil evidence for intermediary stages between major transitions in organic design, indeed our inability, even in our imagination, to construct functional intermediates in many cases, has been a persistent and nagging problem for gradualistic accounts of evolution."

One thing on which today's scientists agree was very well explained by the second author of the theory, Niles Eldredge (1943 - ), is that:

"The record jumps, and all the evidence shows that the record is real: the gaps we see reflect real events in life's history -- not the artifact of a poor fossil record."

Suggested Readings:

• Eldredge, N. and Tattersall, I. (1982), "The Myths of Human Evolution".
• Eldredge, N (1991). "Fossils. The Evolution and Extinction of Species," Photographs by Murray Alcosser. Abrams, New York; Australian edition: Houghton Mifflin; English edition: Aurum Press; German edition: Belser Verlag
• Ernst Mayr (1992), "Speciational Evolution or Punctuated Equilibria," from Albert Somit and Steven Peterson's The Dynamics of Evolution, New York: Cornell University Press, 1992, pp. 21-48.
• Ernst Mayr (2001), What is Evolution

Suggested Websites:

• Fossil Photo galleries

By recovering and sequencing intact DNA from an especially ancient Neandertal specimen, researchers have found evidence suggesting that the genetic diversity among Neandertals was higher than previously thought.

The bigger a dinosaur was, the warmer its blood, a study of the big beasts' fossil remains shows.

A study in the journal Plos Biology now suggests this is not the case, but that bigger dinosaurs may have lost heat so slowly that they stayed warm anyway.

The hominid cranium -- found in two pieces and believed to be between 500,000 and 250,000 years old -- "comes from a very significant period and is very close to the appearance of the anatomically modern human,'' said Sileshi Semaw, director of the Gona Paleoanthropological Research Project in Ethiopia.

Coaxed by a reporter to say Pierolapithecus catalaunicus represented a "missing link," co-author Meike Kohler demurred. "I don't like, very much, to use this word because it is a very old concept."

Kohler added: "This does not mean that just this individual — or even this species, exactly this species — must have been the species that gave rise to everything else which came later in the great ape tree. But it is, if not the species, most probably a very closely related species that gave rise to it."

The only chimpanzee fossils known to science have been unearthed in Kenya, the journal Nature reports.

Another "Hobbit" reference in the literature. I agree with the idea that suggesting that this one-of-a-kind fossil represents a new species is an example of how scientists are too quick in their hypotheses. I personally think that it is much more plausible that this fossil represent a case of microcephaly.

But regardless, as always in this field, we will need to wait and see if any other fossils are found resembling this one with the same cranial capacity of 380 cubic centimeters.

Another amazing dicsovery in China. A bird fossil that's pushing the date of the famous speciation event of flying birds.