Chris Harrison fromDepartment of Marine Geosciences, Rosenstiel School of Marine and Atmospheric Science, University of Miami in a paper in Earth, Planets and Space has sought to resolve the question of the number plates that make up the surface of the earth.
The number of tectonic plates on Earth described in the literature has expanded greatly since the start of the plate tectonic era, when only about a dozen plates were considered in global models of present-day plate motions. With an ever-increasing number of earthquake monitoring sites, improving ocean bathymetry using swath mapping, and the use of space based geodetic techniques, there has been a huge growth in the number of plates thought to exist. In 2003 the total was thought to be 52 delineated on the basis of earthquake epicentre data.
Chris now proposes a total of 159 plates (with some additional smaller plates yet to be mapped).
The largest plate (Pacific) is about 20 % of the Earth’s area or 104 million km2, and the smallest plate is only 273 km2. The Earth is continuously evolving with the continuous creation of new oceanic crust and its destruction in subduction zones. This has a very significant impact on the distribution of continents, movement of water within the worlds oceans (over time) and plays an important part in the evolution of life on this planet.
The number of tectonic plates on Earth described in the literature has expanded greatly since the start of the plate tectonic era, when only about a dozen plates were considered in global models of present-day plate motions. With new techniques of more accurate earthquake epicenter locations, modern ways of measuring ocean bathymetry using swath mapping, and the use of space based geodetic techniques, there has been a huge growth in the number of plates thought to exist. The study by Bird (2003) proposed 52 plates, many of which were delineated on the basis of earthquake locations. Because of the pattern of areas of these plates, he suggested that there should be more small plates than he could identify. In this paper, I gather together publications that have proposed a total of 107 new plates, giving 159 plates in all. The largest plate (Pacific) is about 20 % of the Earth’s area or 104 Mm2, and the smallest of which (Plate number 5 from Hammond et al. 2011) is only 273 km2 in area. Sorting the plates by size allows us to investigate how size varies as a function of order. There are several changes of slope in the plots of plate number organized by size against plate size order which are discussed. The sizes of the largest seven plates is constrained by the area of the Earth. A middle set of 73 plates down to an area of 97,563 km2 (the Danakil plate at number 80, is the plate of median size) follows a fairly regular pattern of plate size as a function of plate number. For smaller plates, there is a break in the slope of the plate size/plate number plot and the next 32 plates follow a pattern of plate size proposed by the models of Koehn et al. (2008) down to an area of 11,638 km2(West Mojave plate # 112). Smaller plates do not follow any regular pattern of area as a function of plate number, probably because we have not sampled enough of these very small plates to reveal any clear pattern.
Saturn’s moons Tethys (in the foreground) & Janus (small irregular moon in the background) – Courtesy Cassini spacecraft – nasa.govThe view was obtained at a distance of approximately 593,000 miles (955,000 kilometres) from Janus. Image scale at Janus is 3.7 miles (6 kilometres) per pixel. Tethys was at a distance of 810,000 miles (1.3 million kilometres) for an image scale of 5 miles (8 kilometres) per pixel.
Janus is a small inner moon of Saturn (radius 90 km and density, 0.63 g/cm3 and orbit 151,470 km) and has a nearly identical orbit to the moon, Epimetheus (not seen in this image). The moons are separated from one another by an astonishingly small 50km. Every four years they swap orbital positions. Janus is heavily cratered with the largest having a radius of 30km. The passage of Janus through the rings of Saturn maintains the sharp edge of the A ring.
Tethys is a mid-sized moon of Saturn (radius 530 km, mean density 0.98 g/cm3, surface gravity 0.15m/s2 and orbit of 294,600 km). Tethys has the lowest density of any of the major moons of Saturn and consists of water ice with just a small fraction of rock. The surface of Tethys is very bright, being the second-brightest of the moons of Saturn after Enceladus, and neutral in color.
Tethys is heavily cratered and cut by a number of large faults and grabens. The largest impact crater, Odysseus, is about 400 km in diameter and the largest graben, Ithaca Chasma, is about 100 km wide and more than 2000 km long.
Moons like Tethys are large enough that their own gravity is sufficient to overcome the material strength of the substances they are made of (mostly ice in the case of Tethys) and mould them into spherical shapes. But small moons like Janus are not massive enough for their gravity to form them into a sphere.
Shenshen Lai and colleagues from the University of British Columbia report results from a study of protein kinases in eukaryotes (A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes.
Protein kinases play a pivotal role in communicating intracellular signals in eukaryotes. The family of eukaryotic protein kinases (ePKs) comprises of at least 568 human members, which accounts for more than 2% of protein coding genes of the entire human genome. These kinases are highly conserved both their primary amino acid sequences in the 3D structures of their catalytic domains. Because of the central regulatory roles the high conservation of the ePKs, the ancestry of these enzymes has become an important question in the study of the evolution eukaryotic organisms.
The ePKs and ChPK are responsible for amongst other things the construction of the cell membrane (which allow the development of organelles including the nucleus to develop) and communication between organelles within the cell. They are likely responsible for the evolution and success of organisms larger than prokaryotic organisms like for example bacteria which lack a nucleus and membrane bounded organelles. Without the early horizontal transfer and preservation of GlnRS life as we know it would likely not exist. GlnRS is found in all complex organisms including plants and animals.
Eukaryotic life is believed to have evolved between 1.7 to 2.7 billion years ago and no living representatives of the earliest eukaryotes survive today. Consequently, the actual origin of protein kinases is difficult to establish with a high degree of confidence.
They conclude that ePKs and ChPKs in eukaryotes evolved from an ancient common mRNA source (possibly at the commencement of life on earth – or at least very early). While these proteins are highly degenerate this team has identified two class-I aminoacyl-tRNA synthetases with high similarities to consensus amino acid sequences of human protein-serine/threonine kinases suggesting that horizontal transfer early in evolution gave rise to many contemporary genes.
This research provides solid argument for the continuity of life on early for much of the last 3 billion years and our genetic relationship to the earliest lifeforms on this planet.
Original Research: Shenshen Lai et al. Evolutionary Ancestry of Eukaryotic Protein Kinases and Choline Kinases, Journal of Biological Chemistry (2016). DOI: 10.1074/jbc.M115.691428
This study looked at the relationship between a high-fat diet and the how this impacted stem and progenitor cell function. They found that a HFD in the mammalian intestine modulated a strong peroxisome proliferator-activated receptor delta (PPAR-delta) response in stem cells. PPAR-delta not only alters the function of intestinal stem cells but importantly non-intestinal progenitor cells nearby allowing the development and growth of intestinal tumors.
Mice on the HFD saw a 30-50% weight gain with a much higher incidence of intestinal tumors than control mice on a normal diet. The researchers saw a significant increase in the number of stem cell in mice on a HFD and importantly the stem cells appeared to grow in a manner which suggested that they were not receiving input immediately adjacent cells – the normal route to cell growth. Non-stem, progenitor cells in the intestinal walls also started to act like stem cells and exhibited significantly longer lives.
There has been clear epidemiological evidence for a strong link between obesity and colorectal cancer and this study provides a clear and concise mechanism for tumor initiation and propagation. If you are on a HFD its time to change.
High-fat diet enhances stemness and tumorigenicity of intestinal progenitors
Little is known about how pro-obesity diets regulate tissue stem and progenitor cell function. Here we show that high-fat diet (HFD)-induced obesity augments the numbers and function of Lgr5+ intestinal stem cells of the mammalian intestine. Mechanistically, a HFD induces a robust peroxisome proliferator-activated receptor delta (PPAR-delta) signature in intestinal stem cells and progenitor cells (non-intestinal stem cells), and pharmacological activation of PPAR-delta recapitulates the effects of a HFD on these cells. Like a HFD, ex vivo treatment of intestinal organoid cultures with fatty acid constituents of the HFD enhances the self-renewal potential of these organoid bodies in a PPAR-delta-dependent manner. Notably, HFD- and agonist-activated PPAR-delta signalling endow organoid-initiating capacity to progenitors, and enforced PPAR-delta signalling permits these progenitors to form in vivo tumours after loss of the tumour suppressor Apc. These findings highlight how diet-modulated PPAR-delta activation alters not only the function of intestinal stem and progenitor cells, but also their capacity to initiate tumours.
Scott Kelly returns to planet surface While watching the NASA coverage of the Soyuz landing in Kazakhstan, I conferenced mother so that she could participate. At 91 and counting she can truly reflect on the advances seen in her lifetime. She recalls being at Eagle Farm (now Eagle Farm Airport) in Brisbane at the age of three when Kingsford Smith landed at 10.50 a.m. on 9 June, 1928. My mother then a 3 year old was in the crowd in Brisbane when he landed.
Scott Kelly returns to planet surface
She recalls the first US space launches and Pacific Ocean landings and the moon landings with great clarity and sees our space exploration endeavours as a reflection of the very best in humanity.
As she says we should be “doing a lot more of this”. She does quite rightly find the conference call remarkable given the feed being from Moscow and the USA over a conference call spanning the SW Pacific, with perfect quality.
Good luck to Commander Scott Kelly – he will surely miss the ability to fly in low gravity now that he is back on earth.