This is about the same age as the first evidence for Archaea, detected by the biological methane left behind in rocks, a gas that is only produced by Archaea nowadays. The oldest records of Bacteria come from microfossils and larger fossilized structures that resemble modern bacterial communities, and date to around 3.5 billion years ago (bya). 2010 PNAS 107(19) c, d, Wikimedia Commons top, bottom e, Wikimedia Commons f, Wikimedia Commons
Figure sources: a, Wikimedia Commons b, adapted from Baker et al. a, b, d, f: transmission electron microscopy c: light microscopy. (e) multicellular Eukaryote, sea star Astropecten articulatus (f) Eukaryotic cell (human white blood cell). (a) Bacteria Bacillus subtilis (b) Archaea ARMAN (c, d) unicellular Eukaryote, microalgae Chlamydomonas sp. Organisms in the other two groups, Bacteria and Archaea, are all unicellular and lack this more complex internal structure.įigure 1 ~ Representatives of major forms of life and their cell structure. Their cells have an internal architecture based on membranes and the DNA is kept inside a nucleus. Eukarya include the familiar plants, animals, and fungi, as well as protists, single-celled creatures such as microalgae.
There are only three major kinds of cellular organisms that form the Tree of Life: Bacteria, Archaea and Eukarya (Figure 1). In order to understand the processes that produce the diversity of life on Earth, evolutionary biologists study the historical relationships of organisms, their phylogeny. Where do we come from? How did all the diversity of life originate? These are some of the most intriguing biological questions we still struggle to answer.
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