Life in the Universe: II. Origin and History of Life on Earth part-2 - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Life in the Universe: II. Origin and History of Life on Earth part-2

The first eukaryotic life forms may be as old as 2 billion years ago. Multicellular algae were common by about 1.2 b.y. ago; wormlike creatures (possibly animals) had appeared by then. Best known among the Eucaryotic algae is Grypania spiralis, found in ancient rocks in Michigan and in Australia. This fossil is preserved because it formed simple shells:

Grypania spiralis.
Grypania spiralis.

Life continued in this primitive state until about a billion and a half years ago when photosynthesis became a common process that helped plant life flourish and released Oxygen. The first multicelled plant is similar to modern brown algae; pieces of this have been found in Chinese rocks dating to about 1.88 billion years ago.

In the Proterozoic (2.5 billion years to 540 million years), life forms slowly changed, with eukaryotic (nucleus) single-celled phylla becoming more diverse. Protozoa (primitive forms) were joined by Metazoa (more advanced) about 1 billion years ago. The first precursors to animals were ancestors to the sponges. Here is an example:

Monosiga Brevicollis, a flagellate that may have been ancestral to the sponges.

The oldest multicellular animal yet discovered is a sponge(like) fossil from rocks in Oman. These date at approximately 710 million years. No actual fossil form was recovered (sponges only have soft parts) but instead a distinctive chemical was found in the carbonate rocks. The telltale sign present in the rocks is a fatty chemical called 24-isopropylcholestane, which scientists have found only in the skeletal structures of demosponges, the most common member of the sponge family

Claims of a unicellular fossil trace in Australian rocks that are about 1.2 billion years old are still in dispute as the evidence could be the result of inorganic activity. Thiomargarita is the name given to markings in Chinese rocks about 600 million years old that have been interpreted as eggs or embryos, and by others as bacteria

The greatest explosion of life in earth history took place about 600 to 500 million years (late Proterozoic into Cambrian) ago with the appearance of distinctive and diverse animal forms. One significant marker was the first appearance of animals with bilateral symmentry at least 600 million years ago. These animals were very small, generally microscopic, and usually found in shales; the samples had to be thin-sectioned by guesswork to find the tiny objects which were preserved soft parts. Representative of these is Vernanimalcula, found in China:

Vernanimlacula, soft parts; the creature possesses bilateral symmetry

Some taxonomists place the appearance of bilateralism even earlier - one school maintains about a billion years ago. The common ancestor to all animals has been named Unilateria (no such fossils have been found). A general scheme for the evolutionary chain of animals follows this lineage:

Cladistic hierarchy of the animals.

A significant upswing in the numbers and diversity of life marks the last 200 million years of the Proterozoic (often referred to as the "Neoproterozoic"). This is a time-stratigraphic chart that introduces Periods that will now be discussed:

Time-stratigraphic column for the Neoproterozoic.
A general view of the life in the time frame from about 605 to 542 million years ago (the Vendian), is found at this New Zealand site which concentrates on the Ediacaran epoch; it mentions Australian and other geographic localities where the assemblages have been found. The fossil life is represented entirely by creatures with soft parts only. It is suggested that these may be ancestral to later phylla observed at the beginning of the Paleozoic. Below is a chart presenting typical Ediacaran fauna, followed by an artist's depiction of life on the sea floor at that time, and beneath that is a layout of some actual fossils:
Biota of Ediacaran age.
Life in the Ediacaran seas.
Some typical Ediacaran fossils.

Two of the most common guide fossils to Vendian life are shown here as actual specimens.

Dickinsonia costata. Springgina floundersi.

By the opening of the Cambrian, many forms of invertebrate life had developed (mainly for protection) external carapaces or coverings that, after death, survive as fossil shells. A survey of Cambrian stratigraphy indicates a dramatic increase in diverse marine life forms, so much so that this abundance of living creatures has been referred to as "The Cambrian Explosion".

Around 535 m.y. ago, in the early Cambrian, a soft parts assemblage of fossil forms has been found in the Chengjiang Formation in Yunnan Province of southern China. Here are typical fossils;

Chengjiang fossils.
The life forms with hard parts make their first appearance in the Middle Cambrian. By far the best locality where both hard and soft parts are well preserved and displayed is in the Burgess black shale of British Columbia (Prof. Charles Walcott is famed for his pioneering studies of this assemblage) deposited about 520 m.y. ago . This sudden burst of evolution may have been tied to Oxygen reaching threshholds near the present day levels. A good review of the types of fossils found there (MacKenzie Mountains) is given by the Peabody Museum at Yale University. Here is an outcrop of this black shale near Mt. Burgess.
The Burgess shale.

This is an artist's conception of typical animal and plant life in the shallow sea in which the Burgess shale was deposited:

Artist's rendition of some of the life forms present in the Burgess shale sea.

Some of the typical life forms in the Burgess shale, each fascinating in its own right, are shown below:

Two animals similar to Trilobites.
Another fossil of the Arthropod type.
A segmented worm.
Halkieria.
Vauxia, an elongate sponge.
Jellyfish imprint in the Burgess shale.

An excellent review of early life on Earth is available at this web site maintained by the University of Munster (unfortunately, many of the links no longer are active).

A second peak time in the abundance of shell-surviving life forms was in the Upper Ordovician (by this time also, the first larger vertebrates, fossil fish, had appeared). Below are two illustrations: the first, an artist' conception of marine invertebrate life in the late Ordovician; the second, a typical slab of Ordovician limestone (from Indiana) containing the fossil types listed in its caption:
A painting depicting a typical Ordovician seafloor, with crinoids, bryozoa, cephalopods, trilobites, and brachiopods.
Slab of Ordovician limestone with a mix of brachiopod, bryozoa, gastropod, and trilobite parts.

The oldest known vertebrate life may be a tiny fish (8 cm in length) called Anatoleptis, of very late Cambrian age (510 million years; younger specimens (470 m/y.) have been found in Scandanavian rocks. The photo below is a microscope view of scales from this fish, whose remains have been found in Wyoming and other parts of North America:

Primitive fish scales associated with other fossil remains of Anatoleptis, possibly the oldest vertebrate found to date; specimen from Wyoming.

Almost nothing is known about life dwelling mainly on land. A small millipede found in rocks in Scotland, dated at 428 million years ago, is a candidate for earliest terrestrial life:

A life form found in Scottish rocks.

There have been several extended time spans (but occuring mainly within single Periods) when major spurts in evolution have witnessed appearances of whole new classes of animal life forms. The Cambrian Explosion described above is the prime example. In the Devonian, the first amphibians (land-dwelling animals), insects, and land trees have been found in the fossil record. A "missing link" (375 million years old) between fish and amphibians was found on Ellesmere Island in the Canadian Arctic. Known as Tiktaalik roseae, it has a crocodilelike head, was 3 meters long, had fins with articulation that foretold jointed legs, and probably could wiggle like a seal on land when not in the sea. Here it is:

Tiktaalik roseae.

We have alluded to the huge increase in animal life since the "Cambrian Explosion" witnessed in the Burgess Shale. This is a good place in the narrative to summarize animal life since the end of the Precambrian.

Animal life from the start of the Paleozoic to the Present.

Although the most ancient life was a mix of single celled plants and animals, we have not touched upon the more advanced forms of life since the Precambrian. A major and vital evolutionary spurt was when marine plant life adapted to living on the land. This began about 480 million years ago. These next two diagrams show the history of land plants:

Evolutionary trend for land plants
The history of land plants.

The illustration below show modern brown algae which were likely progenitors of the land plants.

Brown algae.

By the Devonian land plants, which had started as ferns, club mosses, horsetails, and liverworts (all of these still exist), had established vascular systems, acquired the ability to root in the soil, and were able to propagate using seeds. One of the first giant trees is Archaeopteris, shown in this drawing:

Drawing of Archaeopteris.

A typical plant in this early stage of evolution is Cooksonia, shown here as a fossil frong:

Cooksonia.

The best known locality for early land plant fossils is the Rhynie chert deposits of Scotland:

Panorama describing the Rhynie chert beds.

This drawing below is a reconstruction of a typical Devonian forest:

A forest in the Mid-Devonian.

The Carboniferous forests are among the most diverse in geologic history. Their decay in swamps has produced coal beds world wide.

A Carboniferous forest.

Among the giant plants in the Carboniferous forest shown in this panel were Cordaites, an early relative of conifers; Calamites, a bushy horsetail; Medullosa,a seed fern (a plant with seeds and fern-like leaves); Psaronius, a tree fern; and Paralycopodites and Lepidophloios, lycopsids (scaly, pole-like trees with cones). Lepidophloios could grow to 40 m (132 ft), but most of today�s lycopsids, known as quillworts and club mosses, grow only a few centimeters high.

Illustration by Mary Parrish � Smithsonian Institution

The illustration below shows a cluster of leaves of Pennsylvanian age:

Fossil leaves in a Pennsylvanian rock sample.

The subject of land plants has been glossed over in the above paragraphs. For those seeking more information, consult the Review of plants and the Earliest land plants web sites.

As mentioned in Section 18 and elsewhere, some of the major advances or disappearances in life forms are being attributed to worldwide effects of large impacts. But other causes of these compressed spurts or declines are probably involved in other cases: extreme volcanism; dramatic climate changes; continental splitting, are suggested. These may be manifestations of the "Punctuated Equilibrium" mode of evolutions proposed by Stephen Jay Gould and others.

A rather fanciful panorama of life forms (Kingdoms, Phylla, Families, etc.) from the Late Precambrian to the Present is shown in this mural that is found on the Humboldt State University campus. On the left, pre-Paleozoic animals with soft and hard parts give way to the Invertebrates of the Early Paleozoic, the first fish (Ordovician; sharks in the Devonian), then Amphibians that appeared at about the same time (Mississipian) that land plants took root, with the first reptiles and dinosaurs near the end of the Paleozoic (about the time the first extensive forests spread in the Pennsylvanian), reptiles and small mammals in the Mesozoic, along with the first birds, and finally a dominance of mammals, flowering plants, and widespread forests in the Cenozoic.

The panorama of life found as macrofossils, from about 700 million years ago to the present.
To see entire panel, scroll bottom bar to the right

Missing from the far right of this panel is the story of the hominids, which includes today's mankind. Ancestors to the hominids have been found as far back as 4.5 million years (older animals that may be links are still controversial). This subject is far too involved for any extended treatment in this Tutorial, but the following synopsis touches upon many of the key ideas. The study of ancient precursors to modern humans, is called Paleoanthropology; see this Wikipedia site for a review of mankind's genealogy.

A good, quick overview that carries back to the beginnings of life 4 billion years ago but gives some emphasis to the appearance of humans is found in the Wikipedia Timeline of Human Evolution webpage. Before embarking on the remainder of this page, you should benefit from looking at the list of hominids and their precursors at this Wikipedia list of hominids. These three diagrams are also helpful. The first is a chart that gives a general time line through the Cenozoic and into the end of the Mesozoic; the second shows one version of primate evolution; the third a variation of this with hominids included and broadly spelled out:

More information about the timeline for primate evolution; courtesy Dennis O'Neill.
Phylogeny of the Primates.
Another version of primate evolution.

Classification of the Primates show two broad groupings: 1. The Prosimians, made up of Lemurs, and 2. The Anthropoids, that includes Old and New World monkeys, the Apes, the Chipanzees, and Humans. Of the Anthropoids, there are two major divergences over the last 30 million years. One line includes Old World monkeys, the other contains several branches of which one is the hominids. While the closest tie between Man and other similar animals is said by many to be with the Gorilla or other Apes, the Chimpanzees are also related (98% of the thousands of DNA genes in the genomes of Man and Chimp are identical and located in the same relative positions).

Much publicity has been given to an announcement in May of 2009 of what is called by some as the "missing link" ancestor of both Primate Groups. A nearly complete primate fossil was found in the 1980s in the Messel shale quarry near Frankfurt, Germany. The rocks there are 47 million years in age, placing the many fossil types at Messel in the Eocene.The primate's formal name is Darwinius messelae, but it is called "Ida" (after the daughter of the scientist who led the recent research on it). These two illustrations are pertinent:

Photograph on the left of Darwinius messelae; on the right is a radiograph.
The hand of Ida.

The fossil appears to be a transitional link between the Prosimians and the Anthropoids. It has some lemurlike qualities but lacks certain features of that group while showing some bones that link it to the Anthropoids. Of particular import is the opposable thumb in the hand; this is what is characteristic of primates among mammals and a trait that facilitated the ability of humans to evolve into civilized Man.

We will now concentrate on human evolution, as determined mainly from the fossil record. As a generality, the genus "Homo" is associated with modern humans and direct ancestors whereas the genus "Australopithecus" and others refer to pre-humans. Two diagrams are introduced here. The first emphasizes the time spans during which the various genera lived; the second shows one model (there are competing versions) of the lineage, as a family tree, of the anthropoids back to about 7 million years.

A classification of anthropoid evolution with emphasis on modern human ancestors.
Ancestry of Man in the naturalistic model developed from the concept of Evolution.

Part of this progression can be displayed in terms of an evolutionary pattern that depends on the principal evidence - interpretation of skeletal remains, in this case reconstructed heads.

Another phylogenic classification of the principal hominids.

The diagram below shows the skull differences in a different rendition:

Skulls of various hominids.

This next diagram was taken off the Internet; it is a reproduction of an August 1999 feature article in Time Magazine. It is worth examining before we add comments:

Human genealogy, from a Time Magazine article.

Fossil bones of various hominids have been found on all Old World continents, as evident in this map:

Site map showing localities where pre-modern hominids have been found.

This next map incorporates the above map but shows the general pathway to the New World (N. and S. America). The blue lines are one of several proposed pathways from central Africa to the other continents (discussed below):

Map showing localities where hominid bones and artifacts have been found.

Source: http://rst.gsfc.nasa.gov/