How long did prokaryotes populated earth

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PLoS One 8 :e Increased abundance of Sutterella spp. Mol Autism 4 Probiotics in gastroenterology: indications and future perspectives. Scand J Gastroenterol Suppl 38 —6. Molecular approaches to the role of the microbiota in inflammatory bowel disease. Prokaryotes are ubiquitous. They cover every imaginable surface where there is sufficient moisture, and they also live on and inside virtually all other living things. In the typical human body, prokaryotic cells outnumber human body cells by about ten to one.

They comprise the majority of living things in all ecosystems. Some prokaryotes thrive in environments that are inhospitable for most living things. Prokaryotes recycle nutrients —essential substances such as carbon and nitrogen —and they drive the evolution of new ecosystems, some of which are natural and others man-made.

Prokaryotes have been on Earth since long before multicellular life appeared. Indeed, eukaryotic cells are thought to be the descendants of ancient prokaryotic communities. When and where did cellular life begin? What were the conditions on Earth when life began? We now know that prokaryotes were likely the first forms of cellular life on Earth, and they existed for billions of years before plants and animals appeared.

The Earth and its moon are dated at about 4. This estimate is based on evidence from radiometric dating of meteorite material together with other substrate material from Earth and the moon. Yet others think that cyanobacteria began pumping out oxygen as early as 2. Methane reacts with oxygen, removing it from the atmosphere, so fewer methane-belching bacteria would allow oxygen to build up.

When the ice eventually melts, it indirectly leads to more oxygen being released into the atmosphere. First undisputed fossil evidence of cyanobacteria, and of photosynthesis : the ability to take in sunlight and carbon dioxide, and obtain energy, releasing oxygen as a by-product.

There is some evidence for an earlier date for the beginning of photosynthesis, but it has been called into question. One key organelle is the nucleus: the control centre of the cell, in which the genes are stored in the form of DNA. The engulfed bacteria eventually become mitochondria , which provide eukaryotic cells with energy. The last common ancestor of all eukaryotic cells had mitochondria — and had also developed sexual reproduction.

Later, eukaryotic cells engulfed photosynthetic bacteria and formed a symbiotic relationship with them. The engulfed bacteria evolved into chloroplasts: the organelles that give green plants their colour and allow them to extract energy from sunlight. Different lineages of eukaryotic cells acquired chloroplasts in this way on at least three separate occasions, and one of the resulting cell lines went on to evolve into all green algae and green plants.

The eukaryotes divide into three groups: the ancestors of modern plants, fungi and animals split into separate lineages , and evolve separately. We do not know in what order the three groups broke with each other. At this time they were probably all still single-celled organisms. The first multicellular life develops around this time. It is unclear exactly how or why this happens, but one possibility is that single-celled organisms go through a stage similar to that of modern choanoflagellates : single-celled creatures that sometimes form colonies consisting of many individuals.

Of all the single-celled organisms known to exist, choanoflagellates are the most closely related to multicellular animals, lending support to this theory. The early multicellular animals undergo their first splits. First they divide into, essentially, the sponges and everything else — the latter being more formally known as the Eumetazoa.

Around 20 million years later, a small group called the placozoa breaks away from the rest of the Eumetazoa. Placozoa are thin plate-like creatures about 1 millimetre across, and consist of only three layers of cells.

It has been suggested that they may actually be the last common ancestor of all the animals. The comb jellies ctenophores split from the other multicellular animals. Like the cnidarians that will soon follow, they rely on water flowing through their body cavities to acquire oxygen and food.

The ancestor of cnidarians jellyfish and their relatives breaks away from the other animals — though there is as yet no fossil evidence of what it looks like. Around this time, some animals evolve bilateral symmetry for the first time: that is, they now have a defined top and bottom, as well as a front and back. Little is known about how this happened. However, small worms called Acoela may be the closest surviving relatives of the first ever bilateral animal. It seems likely that the first bilateral animal was a kind of worm.

Vernanimalcula guizhouena , which dates from around million years ago, may be the earliest bilateral animal found in the fossil record. The Bilateria , those animals with bilateral symmetry, undergo a profound evolutionary split.

They divide into the protostomes and deuterostomes. The deuterostomes eventually include all the vertebrates, plus an outlier group called the Ambulacraria. The protostomes become all the arthropods insects, spiders, crabs, shrimp and so forth , various types of worm, and the microscopic rotifers. The first hole that the embryo acquires, the blastopore, forms the anus in deuterostomes, but in protostomes it forms the mouth.

The earliest known fossils of cnidarians , the group that includes jellyfish, sea anemones and corals, date to around this time — though the fossil evidence has been disputed. Strange life forms known as the Ediacarans appear around this time and persist for about 33 million years. A small group breaks away from the main group of deuterostomes, known as the Ambulacraria.

This group eventually becomes the echinoderms starfish, brittle stars and their relatives and two worm-like families called the hemichordates and Xenoturbellida.