Palaeos: Overview
United States Geology Service drawing (public domain) of deep time, showing the history of life through geological time. In this diagram, one starts with the formation of the Earth, four and a half billion years ago (shown as the small dot at the lower left) and continue through the vast expanse of Precambrian time, before arriving at the Cambrian period, which marked the start of the Phanerozoic Eon and the appearance of complex life (although there is a tendency now to backdate this to the Ediacaran). Moving clockwise, through a succession of invertebrate types in the sea, we can follow the conquest of the land, the rise of insects and reptiles, and the dominance of the dinosaurs on land and marine reptiles in the sea. With the extinction of the Mesozoic megafauna (no asteroid is shown here, and the style of art predates the dinosaur renaissance of Ostrom and Bakker), there is a succession of primitive and then more advanced mammals, and finally paleolithic humans and modern towns and cities (these details are only visible in the large image). |
Overview
It is hard to provide an overview for a project as huge and rambling as Palaeos, so this page only some of the more basic categories and starting pages.
There are basically two orientations that can be taken here. One is to follow the sequence of Time, the other Evolution.
From the paleontological perspective of Palaeos, time is presented as the geological timescale, and life as the the evolutionary tree of life on Earth. These two pages can serve as starting points, from which other related and interrelated pages and topics can be explored. On the basis of the geological timescale there are seven major timescale units (eras and eons). Although in the above diagram there are seven major evolutionary categories (others have proposed similar or different classifications), as far as life on Earth goes we have arbitrarily divided our coverage into six main units (kingdoms and domains of life). Allowing for the unevenness of coverage, Palaeos can be summarised as follows:
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Time, or more specifically the geological time-scale is here used to define the major stages in the history of life on Earth. Here the four and a half billion year history of planet Earth is divided into seven segments, although once again this is semi-informal classification, mixing eons and eras. These are:
- the Chaotian, a new eon which was too good to leave out,. Why start with the origin of the Earth when you begin with the origin of the Solar System?
- the Hadean witnessed the formation of the Earth and, quite possibly, the origin of life
- the Archean was the age of early bacteria, Stromatolites, and the reducing atmosphere. For over a billion years in which the Earth was inhabited by nothing more advanced than algal mats.
- the Proterozoic was a dramatic time. There was the oxygen crisis—being a crisis for anaerobic bacteria, in that photosynthetic blue-green algae totally transformed the Earth by changing the atmosphere from reducing to oxygenating, thus paving the way for higher life. Other notable events were snowball earth, the rise of Eukarya, and the origin of multicellular life.
- The Phanerozoic, the fourth and most recent eon, the time of diverse life, complex ecosystems, and an oxygen-rich atmosphere. This is divided into:
- the Paleozoic, the first and longest of the eras of complex life, which witnessed the Cambrian explosion, invertebrates, fish, and early land plants, amphibians and reptiles
- the Mesozoic, the age of giant dinosaurs, marine reptiles, ammonites, gymnosperms, and primitive mammals
- the Cenozoic, the age of mammals and birds, and modern taxa of plants and invertebrates, this being the era we are still in. Each of these eras is characterised by a mass-extinction, which in each case wiped out the dominant life-forms and paved the way for the next group of organisms. Unfortunately, human activities, overpopulation, and over-exploitation and degradation of the environment is currently bringing about a new mass-extinction, and as we enter a new, Anthropocene or Anthropozoic era, the future is very uncertain. I am intending to add a few pages here to cap off the grand narrative of the three and a half to four billion year history of life on Earth and possibilities of life, and human, future evolution.
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Cosmic evolution includes everything from the Big Bang to the formation of galaxies and stars (which set the stage for the formation of the Solar System and the Earth (which goes under "Chaotian" and "Hadean" respectively) and to the evolution of minerals, the Earth, life, and mind. Most of these topics are very incomplete, nor is there currently any intention to describe them at length, as the focus of Palaeos is exploring the history and genealogy of life on Earth through time. Although the number and details of kingdoms of life differ, we have decided as far as main categories go to follow by default an informal approach that broadly follows the The Five Kingdom paradigm of Robert Whittaker and Lynn Margulis. Adding the now pretty much meaningless (in terms of modern systematics) 19th Century distinction of vertebrates and invertebrates gives the following six categories:
- Bacteria the simplest and oldest forms of life, such as the various types of bacteria and blue-green algae, which don't have a distinct cellular nucleus. Included here are two distinct domains: Eubacteria and Archaea.
- Eukarya or eukaryotes are organisms with a complex cellular structure and distinct nucleus, the third domain of life. Here there are a huge diversity of unicellular forms, masking up the majority of the group. The remaining Eukarya (or Eucarya, depending on the spelling) make up the three kingdoms of multicellular life of the the Whittaker–Margulis scheme:
- Plants, which need no introduction (our coverage of the more advanced taxa (gymnosperms and flowering plants) is still quite basic at the time of writing),
- Fungi, not quite animals and not quite plants (again we don't have that much on them, though hopefully this will change),
- and the Metazoa or animals. These are divided anthropocentrically and totally colloquially into Vertebrates and Invertebrates.
- Invertebrates is another way of saying all metazoa (multicellular animals) except for higher chordates. That this outmoded classification is retained is because paleontology, biology, and popular understanding still refers to animal life in terms of vertebrate and invertebrate. Mostly small, they are often overlooked in favour of their backboned brethren, although a microscope or even a hand lens will reveal creatures as astonishing as those that one might imagine would inhabit an alien world. Marine forms with hard parts have a very good fossil record, and a few these groups are covered here.
- Vertebrates include all those large charismatic animals. Much as Palaeos started out as Toby White's Vertebrate Notes, and anyway who doesn't love ichthyosaurs, dinosaurs and other exotic prehistoric creatures? So not surprisingly this is the clade is given the most detailed coverage on these pages.
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Finally there are a number of additional pages. Because the science featured in Palaeos doesn't come from nowhere, Scientists features a very incomplete alphabetical listing of (short biographies, along with occasional links) of paleontologists and other scientists who over the centuries have constructed, and continue to construct, the vast edifice of knowledge of the history of life on Earth (and related topics), whilst a timeline traces both the history of discoveries and their interplay with popular culture. Resources will, eventually, hopefully, include a directory of links to other paleo web sites and blogs, useful books, journals, and so on. Authors will give a very brief listing of contributers to Palaeos.
Navigating Palaeos
In keeping with Toby's original Vertebrate Notes, Palaeos has a somewhat modular structure, being divided into "units". Therefore. in addition to the dual hierarchy of time and life, an attempt has been made to retain the modular and hierarchical approach here. Unfortunately it hasn't worked out as tidily as we would have liked, because each subject has so many ramifications and links to other topics in other hierarchies and units. Ideally, units are divided into pages, and also may have daughter units, which may in turn have subunits, and so on with maddening detail. The menu bars at the top and bottom of each page (including this one) present navigation options such as Page Back and Page Next, and Unit Up, Unit Down, Unit Back, Unit Next, and Unit Home. Page Back, Page Next, and Unit Home allow you to navigate "horizontally" (at the same hierarchical level) within the unit, and Unit Back and Unit Next between units of the same level. This may be through either similar or different (alternating life and time, e.g. Archean – Bacteria – Proterozoic – Eukarya – Paleozoic) units, or both. So on the Eukarya (or Eucarya) index page, Unit Back in the similar series goes to Bacteria and Unit Next to Plants, these all being on the same level. Whereas dissimilar (alternating) goes from Eukarya back to Proterozoic (when eukaryotes emerged and diversified) and next to Paleozoic (when they flourished beginning with the Cambrian explosion). As for the vertical button (which is always similar), Unit Up goes to the larger unit that includes Eukarya, which is Tellurobiota (Life on Earth). As with Unit Up, Unit Down navigate "vertically". Since each higher level unit will generally have several daughter units, Unit Down only goes to the first of these (according an arbitrary or non-arbitrary arrangement) after which Unit Next goes to the next unit in the group. So with for example the Palaeozoic index page, Unit Down goes to the Cambrian index page (the Cambrian being the first period of the Paleozoic era), and you need to click on Unit Next for the Ordovician (the next geological period in the sequence). Sometimes page and unit categories are the same, so on the page that follows the Unit index/home page, Page Back and Unit Home are the same, in which case there's some duplication, which is allowed for the sake of consistency of menu boxes. With the last page (usually a references page) of a unit, Page Next goes to the first page of the next unit, although Unit Next goes to the similar page of the next unit (in this case the corresponding references page). Sometimes the units and pages are linked in a logical series, for example the sequence of the geological timescale, or the standard series of organisms in biology books (prokaryotes (bacteria), eukaryotes, plants, fungi, animals) or other phylogenetic listings. At other times the listing is more arbitrary. In addition to the usual Unit Next and Page Next listing, there may be additional links to non-standard pages such as glossaries and notes.
In addition to the main menu bars at the top of the page, there is an abbreviated navigation bar at the bottom, and a listing of sub-topics and related topics under the main navigation bar.
Because of the scale of the task, it is likely that many menu links may not follow the right order. In such cases, please contact me (see email address at bottom of this page)
Types of pages
Palaeos includes several different types of pages, which together make up a Unit (although different units may include different types of pages).
Each unit starts with an index or home page. This may give a brief overview or a detailed introduction, depending on the idiosyncrasy of the author and topic. Eventually there will be more standardisation here, with the detailed intro being moved to an overview page.
Ordinary pages, such as this one, generally have a white background (apart from the geological timescale pages and some of the taxonomic pages). They follow after the index/home page of the unit.
Major Units may include a Glossary page or pages. These constitute an abbreviated coverage of each topic. Glossary listings will point to other listings, and where "more" appears it is to the main page on the topic. Sometimes there is also an external link or links, which are indicated as such
After the glossary page (if present) there is, in the case of the units on each of the groups of organisms, a Dendrogram (phylogenetic tree or, colloquially "cladogram") page. This has a green background (symbolising the tree of life). Here the Page Back, Page Next, and Unit Home, refer to navigation within the dendrogram page's Unit; i.e. to a non-dendrogram page, whereas Unit Back, Unit Next, and Unit Up will take you to the corresponding dendrograms (evolutionary trees) for those Units. The only time Unit Home points to a dendrogram page is when it points back to the dendrogram index pages .
The Reference pages is, you guessed it, for the references for each unit. As with dendrogram menus, Unit Back, Unit Next, and Unit Up will take you to the corresponding reference pages of those Units. The reference page is always at the end of a unit, so Page Next on a reference page always points to the Index page of the next unit.
Lists, of taxa or whatever, may be included as distinct pages or as part of the index/home page. So far there are not many of these due to the incompleteness of Palaeos and the usefulness of Google search. Notes, and Pieces are miscellaneous pages that don't fit in the above categories.
Currently the new Palaeos is still a work in progress, so if you would like to suggest or contribute material, please contact the editors at the email addresses provided below.
