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GS Paper: GS1-15.Geographical features and their location- Changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.

  • Earth’s seismic noise levels

    Scientists at the British Geological Survey (BGS) reported a change in the Earth’s seismic noise and vibrations amid the coronavirus lockdown. This change has been monitored through a space-based seismograph.

    Ever heard of space-based monitoring of seismic activities?  This topic creates a scope for potential prelims question…

    What is seismic noise?

    • In geology, seismic noise refers to the relatively persistent vibration of the ground due to a multitude of causes.
    • It is the unwanted component of signals recorded by a seismometer– the scientific instrument that records ground motions, such as those caused by earthquakes, volcanic eruptions, and explosions.
    • This noise includes vibrations caused due to human activity, such as transport and manufacturing, and makes it difficult for scientists to study seismic data that is more valuable.
    • Apart from geology, seismic noise is also studied in other fields such as oil exploration, hydrology, and earthquake engineering.

    How are vibrations generated?

    • We measure ground vibrations from earthquakes using seismometers.
    • These are incredibly sensitive so they also pick up other sources of vibration too, including human activity, such as road traffic, machinery and even people walking past.
    • All these things generate vibrations that propagate as seismic waves through the Earth.

    Reasons for the decline

    • Due to the enforcement of lockdown measures around the world to tackle the novel coronavirus pandemic, the Earth’s crust has shown reduced levels of vibration.

    How do the reduced noise levels help scientists?

    • The seismic noise vibrations caused by human activity are of high frequency (between 1-100 Hz), and travel through the Earth’s surface layers.
    • Usually, to measure seismic activity accurately and reduce the effect of seismic noise, geologists place their detectors 100 metres below the Earth’s surface.
    • However, since the lockdown, researchers were able to study natural vibrations even from surface readings, owing to lesser seismic noise.
    • Due to lower noise levels, scientists are now hoping that they would be able to detect smaller earthquakes and tremors that had slipped past their instruments so far.

     

  • [pib] Ionospheric based monitoring of large earthquakes

    Scientists of Indian Institute of Geomagnetism (IIG) an autonomous institution of the DST have extensively studied the signatures of recent large earthquakes into the ionosphere with an ambitious aim to derive the seismic source characteristics from the ionosphere.

    CLAIMS

    • The research is a part of the interdisciplinary program ‘Coupled Lithosphere-Atmosphere- Ionosphere-Magnetosphere System (CLAIMS)’ of IIG.
    • CLAIMS focuses on energy transfer to the atmosphere during solid Earth processes such as earthquakes as well as tsunamis.

    Key terms: Co-seismic Ionospheric Perturbations (CIP)

    • In general, the Earth crust uplift during an earthquake produces compressional (i.e. pressure) waves in the overlying atmosphere.
    • These waves propagate upward in the region of exponentially decreasing atmospheric neutral density, and thus, wave amplitude increase with atmospheric heights.
    • On arrival at ionospheric heights, the waves redistribute ionospheric electron density and produce electron density perturbations (disruption) known as CIP.

    Objective of CLAIMS

    • The spatial distribution of near field co-seismic Ionospheric perturbations (CIP) associated with this event could reflect well the ground deformation pattern evolved around the epicentre.
    • These CIPs were derived using the Global Positioning System (GPS) measured Total Electron Content (TEC).
    • The CIP distribution was estimated at Ionospheric piercing point (IPP) altitude.

    Other factors affecting CIP

    The major effective non-tectonic forcing mechanisms at ionospheric altitudes are the-

    1. orientation between the ambient geomagnetic field and seismic induced neutral wave perturbations.
    2. orientation between the moving satellite line of sights and the wave perturbations.
    3. ambient ionospheric electron density gradient.

    Back2Basics

    Ionosphere

    • The ionosphere is the ionized part of Earth’s upper atmosphere, from about 60 km to 1,000 km altitude.
    • It is a region that includes the thermosphere and parts of the mesosphere and exosphere.
    • It is ionized by solar radiation.

  • Pink Supermoon/ Paschal Moon

    A supermoon is all scheduled to show up in the sky on April 7. It would be the biggest and brightest full moon of 2020.

    Pink Supermoon

    • According to NASA, a supermoon takes place when a full moon is at its closest to the Earth.
    • When the full moon appears at perigee (closest point from the earth) it is slightly brighter and larger than a regular full moon — and that is what we call a “supermoon.”
    • They are called Supermoons because they are 7 per cent bigger and 15 per cent brighter, compared to an average full Moon.
    • The moon will not be originally pink in colour. It got its name from the pink wildflowers – Wild Ground Phlox – that bloom in the spring and are native to North America.
    • It is also called Paschal moon because, in the Christian calendar, this is used to calculate the date for Easter – the first Sunday after the Paschal Moon is Easter Sunday.

  • Earth’s spin has slowed over time

     

    Earth spun 372 times a year 70 million years ago, compared to the current 365. This means the day was 23½ hours long, compared to 24 today.

    Faster Earth in the olden days

    • It has long been known that Earth’s spin has slowed over time.
    • Previous climate reconstructions, however, have described long-term changes over tens of thousands of years.
    • The new study looked at daily and annual variations in the mollusc shell.

    About the Mollusc

    • A mollusc is an invertebrate of a large phylum which includes snails, slugs, mussels, and octopuses. They have a soft unsegmented body and live in aquatic or damp habitats, and most kinds have an external calcareous shell.
    • The ancient mollusc, Torreites Sanchez, belonged to an extinct group called rudist clams.
    • At 70 million years ago, it belonged to the Late Cretaceous — it was around the time this epoch ended, some 65 million years ago, that dinosaurs went extinct.

    How did researchers conclude this variation?

    • Torreites sanchezi grew very fast, laying down daily growth rings.
    • Using lasers on a single individual, scientists sampled tiny slices and counted the growth rings accurately.
    • This allowed them to determine the number of days in a year 70 million years ago, and more accurately calculate the length of a day.

    Significance of the research

    • It is important to note that the period of Earth’s orbit has remained the same. In other words, one year 70 million years ago was as long as one year today.
    • However, if there were a calendar then, the year would have been 372 “days” long, with each “day” half-an-hour shorter than one day today.
    • Today, Earth’s orbit is not exactly 365 days, but 365 days and a fraction, which is why our calendars have leap years, as a correction.

    The Moon’s retreat

    • Friction from ocean tides, caused by the Moon’s gravity, slows Earth’s rotation and leads to longer days.
    • And as Earth’s spin slows the Moon moves farther away at 3.82 cm per year.
    • If this rate is projected back in time, however, the Moon would be inside the Earth only 1.4 billion years ago.
    • This new measurement, in turn, informs models of how the Moon formed and how closes it has been to Earth over their 4.5-billion-year gravitational relationship.

  • [pib] Effects of Himalayan slip on its Hydrology

    Researchers from the Indian Institute of Geomagnetism have found the mighty Himalayas subside and move up depending on the seasonal changes in groundwater.

    Tectonic activity and groundwater

    • The Himalayan foothills and the Indo-Gangetic plain are sinking because its contiguous areas are rising due to tectonic activity associated with landmass movement or continental drift.
    • The new study shows that subsidence and uplift are found to be associated with seasonal changes in groundwater, apart from the normal, common reasons.
    • Water acts as a lubricating agent, and hence when there is water in the dry season, the rate of the slip of the fault in this region is reduced.
    • In the Himalaya, seasonal water from glaciers, as well as monsoon precipitation, plays a key role in the deformation of the crust and the seismicity associated with it.
    • The subsidence rate is associated with groundwater consumption.

    Findings of the study

    • The researchers have made the combined use of GPS and Gravity Recovery And Climate Experiment (GRACE) data, which has made it possible for them to quantify the variations of hydrologic mass.
    • The GRACE satellites, launched by the US in 2002, monitor changes in water and snow stores on the continents.
    • The combined data suggest a 12% reduction in the rate of the subsurface slip. This slip refers to how fast the fault is slipping relative to the foot and hanging wall.
    • The slip occurs at the Main Himalayan Thrust (MHT), due to hydrological variations and human activities, over which there is the periodic release of accumulated strain.

    About GRACE Mission

    • The Gravity Recovery and Climate Experiment (GRACE) was a joint mission of NASA and the German Aerospace Center.
    • Twin satellites took detailed measurements of Earth’s gravity field anomalies from its launch in March 2002 to the end of its science mission in October 2017.
    • By measuring gravity anomalies, GRACE showed how mass is distributed around the planet and how it varies over time.

     

  • Solar Storms

     

    According to a research, sudden releases of high-energy particles from the sun, called solar storms, can mess with the navigational ability of gray whales, causing them to strand on land.

    Solar storms

    • Solar storms are a variety of eruptions of mass and energy from the solar surface.
    • Flares, prominences, sunspots, coronal mass ejections are the common harbingers of solar activity, as are plages and other related phenomena seen at other wavelengths.

    Impact on Whales

    • Solar storms have the potential to modify geomagnetic field and disrupt magnetic orientation behaviour of animals, hampering their navigation during long periods of migration.
    • They disrupt earth’s magnetic field — and the whales’ navigational sense.
    • The radio frequency noise created by the solar outburst affects the whales’ senses in a way that prevents them from navigating at all.

  • Yongle Blue Hole (YBH)

     

    Carbon more than 8,000 years old has been found inside the world’s deepest blue hole — the Yongle Blue Hole (YBH).

    Yongle Blue Hole (YBH)

    • The deepest known marine cavern is the Yongle blue hole, which measures roughly 300 metres from top to bottom.
    • Blue holes are marine caverns filled with water and are formed following dissolution of carbonate rocks, usually under the influence of global sea level rise or fall.
    • Its waters are mostly isolated from the surrounding ocean and receive little fresh water from rainfall, making it a rare spot to study the chemistry of oxygen-deprived marine ecosystems.
    • What distinguishes them from other aquatic caverns is that they are isolated from the ocean and don’t receive fresh rainwater.
    • They are generally circular, steep-walled and open to surface.

    Significance of YBH

    • YBH has a depth of 300 metres, far deeper than the previously recorded deepest blue hole, Dean’s Blue Hole in Bahamas, which had a depth of 202 metres.
    • However, like most blue holes, it is anoxic i.e. depleted of dissolved oxygen below a certain depth. This anaerobic environment is unfavorable for most sea life.
    • Such anoxic ecosystems are considered a critical environmental and ecological issue as they have led to several mass extinctions.
    • Concentrations of carbon, usually found in deep marine holes like YBH, provide a natural laboratory to study carbon cycling and potential mechanisms controlling it in the marine ecosystem.
    • The transition from aerobic to anaerobic environment adversely affects the biogeo-chemistry of the ocean.

  • Why do we have Leap Years?

     

    The year 2020 is a ‘leap year’, meaning the month of February will have 29 days instead of 28, and the total number of days will be 366 instead of 365. This was also the case in 2016, and 2024 will again be a leap year.

    Leap Years

    • A calendar is meant to correspond to the Earth’s seasons.
    • For this, the number of days in a calendar needs to match the time required by the Earth to orbit the Sun.
    • The time required by the Earth to complete its orbit around the Sun is approximately 365.242 days. But years are usually only 365 days.
    • To adjust for the extra 0.242 days in the orbital period, which becomes almost one full day in four years, the calendar adds an extra day once every four years.
    • This approximates the time to 365.25 days, which is close to the actual 365.242 days.

    But is that not inaccurate?

    • Yes, it is. And further adjustments are made to the Gregorian calendar, the calendar we follow today.
    • The Gregorian calendar was introduced in 1582. Before that, the calendar followed was the Julian calendar, introduced in 45 BC.
    • The calendars were different in their treatment of leap years.
    • The Julian calendar had leap days every four years, but since it still did not accurately conform to the Earth’s precise orbit time, it kept falling behind with respect to natural seasons over the centuries.
    • By the 16th century, the Julian calendar had fallen out of tune with the natural seasons by almost 10 days.
    • To correct this discrepancy, Pope Gregory XIII in 1582 decreed that the day of October 4 that year would be followed directly by October 15 – thus covering up the error.
    • The Pope also modified the leap year system in the Julian calendar. That new system came to be known as the Gregorian calendar.

    What is the new system?

    • In the Gregorian calendar, a century year (a year ending with 00) is not a leap year, even though it is a multiple of 4. Thus, the year 2100 will not be a leap year.
    • But even this does not provide total accuracy. To ensure that, some century years remain leap years. In the Gregorian calendar, leap years include those century years which are exactly divisible by 400.
    • Thus, 2000 remained a leap year even though it ended with 00.
    • The Gregorian calendar reduces the margin of error under the Julian calendar, thus keeping days more in tune with seasons.

  • Specie in news: ‘World’s largest’ subterranean fish

     

    Systematic exploration of the Meghalayan caves has been underway for almost 30 years and hundreds of kilometres of cave passages have been explored and mapped. In a cave in a remote forested area of Meghalaya’s Jaintia Hills a research expedition found large specie of a subterranean fish (occurring under the earth’s surface).

    About the fish

    • The blind fish was over 40 cm. It has not been named so far.
    • It is nearly five times the mean length (85mm/8.5 cm) for all known subterranean fish to date.
    • The only other species exceeding 300mm (30 cm) in length are eel-like Synbranchidae with nothing like the bulk of the new fish.
    • The 250-known subterranean (occurring under the earth’s surface) fish species around the world measure only around 8.5 cm on average.
    • The specialists say that possibly one (or more) populations of these fish became isolated deeper in the caves and over generations became adapted to the dark, losing their eyes in the process.

    Closest resemblance

    • The experts feel that the fish species is very similar to the Golden Mahseer or the Tor Putitora, one of the most famous game fish of the Himalayan rivers.
    • Unique characters that distinguishes it from the Golden Mahseer is the lack of pigmentation, a lack of eyes and of course, its subterranean habitat – being locked in caves.
    • There are ‘normal’ Golden Mahseer in the area too but there is not much surface water (at least in the dry winter months) so fish end up in the cave pools and underground rivers.

    Features of Subterranean ecosystems

    • Subterranean ecosystems are considered extreme, high-stress environments characterised by darkness, truncated food webs and food scarcity.
    • Despite this, they harbour exceptional vertebrate and invertebrate taxa (21,000+ species), many of which are evolutionarily unique, and relics of ancient fauna given their long-term isolation.
    • Many cave fish show different adaptations – some don’t have eyes, some have reduced eyes, some don’t have fins, some have weird body shapes.

  • Species in news: Thanatotheristes

     

    Scientists have found that a dinosaur fossil, found in Alberta in Canada in 2010, belongs to a new species of tyrannosaur. They have named it Thanatotheristes, which means “reaper of death”.

    Thanatotheristes

    • Tyrannosaurs were one of the largest meat-eating dinosaurs to have ever lived, with very large and high skulls, and the best known among them is the Tyrannosaurus rex, celebrated in the Jurassic Park series.
    • The 79-million-year-old fossil that the researchers have found is the oldest tyrannosaur known from northern North America.
    • Thanatotheristes preyed on large plant-eating dinosaurs such as the horned xenoceratops and the dome-headed colepiochephale.
    • The research suggests that tyrannosaurs did not have one general body type; rather different tyrannosaur species evolved distinct body sizes, skull forms and other such physical features.
    • The fossil specimen is important to understand the Late Cretaceous period, which is the period when tyrannosaurs roamed the Earth.