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.

Using leaf fossils, researchers have found that the Indian monsoon 25 million years ago resembled present-day Australia’s.

Try this PYQ:

Q.Which one of the following is the appropriate reason for considering the Gondwana rocks as the most important rock systems of India?

(a) More than 90% of limestone reserves of India are found in them

(b) More than 90% of India’s coal reserves are found in them

(c) More than 90% of fertile black cotton soils are spread over them

(d) None of the reasons given above is appropriate in this context

India’s drift

• About 180 million years ago, India separated from the ancient supercontinent Gondwana and took a long northward journey of about 9,000 km to join Eurasia.
• During this journey, the subcontinent moved from the southern hemisphere, crossed the Equator to reach its current position in the northern hemisphere.
• Due to these changing latitudes, it experienced different climatic conditions, and a new study has now tried to map these climatic variations using leaf fossils.

Clueless over the evolution of monsoon

• The evolution of the monsoonal climate in India is still debatable and not fully understood.
• Though recent data indicates that the monsoon system we experience now dates back to about 25 million years, it is still unclear how the climate was during its long voyage.

Indian research

• The researchers analysed the morphological characters of fossil leaves collected from Deccan Volcanic Province, East Garo Hills of Meghalaya, Gurha mine in Rajasthan and Makum Coalfield in Assam.
• The four fossil assemblages were found to be from four different geological ages.
• It has been observed from across the globe that plant leaf morphological characters such as apex, base and shape are ecologically tuned with the prevailing climatic conditions.
• The research applied this model to characterize the past monsoon from fossil leaves.

It’s finding

• The results indicated that the fossil leaves from India were adapted to an Australian type of monsoon and not the current Indian monsoon system during its voyage.
• The reconstructed temperature data show that the climate was warm (tropical to subtropical) at all the studied fossil sites with temperatures varying from 16.3–21.3 degrees C.
• All the fossil sites experienced high rainfall, which varied from 191.6 cm to 232 cm.

Bhimbetka, which has yielded a fossil of Dickinsonia dating back about 550 million years, is the first time the particular fossilized organism has been recorded in India.

Why does this fossil matter?

• It dates back to an era regarded as the precursor to the explosion of life on earth during the Cambrian period.
• Thus it puts India firmly on the map for studies of the Ediacaran era along with Australia and Russia.

Here’s what makes the discovery a global milestone:

(a) Ediacaran Period

• The finding gives lead about the earliest living species during a period of the earth’s history known as the Ediacaran, named after the Ediacara Hills in South Australia.
• This is the period in Earth’s history when Dickinsonia and several multicellular organisms existed.
• It was approximately 635 million years ago (Ma) and 541 Ma, with the living creatures of the era, called vendobionts.

Now take this opportunity to revise the Geological time scale from your NCERTs. Try differentiating between different era, periods and epoch.

(b) India’s Proximity to Australia

• Studies of the rock characteristics in and around Bhimbetka show that they share several characteristics with rocks in Australia.
• Dickinsonia fossils from India were found by the scientists to be identical to the Rawnsley Quartzite in South Australia.
• This provides evidence of their age and the proximity of the two landmasses in Gondwanaland in that era.
• The evidence however did not support reconstructions adjusted for the polar wander phenomenon [which involves motion of continents over geologic time and its impacts].

 Use of Zircon dating

• The age of fossil rock is determined using Zircon isotopes.
• Zircon dating of the youngest Maihar sandstone in Madhya Pradesh puts its age at 548 Ma.
• The lower Bhander group in the Son and Chambal valleys yielded an isotope-derived age for limestones ranging from 978 Ma to 1073 Ma, situating it in the older Tonian period.
• The Ediacaran period was the precursor to the Cambrian (about 541 Ma to 485.4 Ma) when the earth witnessed an explosion of life forms and much of which makes up modern animal life today.

Yesterday, December 21, was Winter Solstice, the shortest day of the year in the Northern Hemisphere. In the Southern Hemisphere, conversely, it was Summer Solstice, the year’s longest day.

Try this MCQ:

Q.On 21st June, the Sun

(a) Does not set below the horizon at the Arctic Circle

(b) Does not set below the horizon at Antarctic Circle

(c) Shines vertically overhead at noon on the Equator

(d) Shines vertically overhead at the Tropic of Capricorn

Why are the hours of daylight, not the same every day?

• The explanation lies in Earth’s tilt.
• And it’s not just the Earth — every planet in the Solar System is tilted relative to their orbits, all at different angles.
• The Earth’s axis of rotation is tilted at an angle of 23.5° to its orbital plane.
• This tilt — combined with factors such as Earth’s spin and orbit — leads to variations in the duration of sunlight than any location on the planet receives on different days of the year.

Impact of the tilted axis

• The Northern Hemisphere spends half the year tilted in the direction of the Sun, getting direct sunlight during long summer days.
• During the other half of the year, it tilts away from the Sun, and the days are shorter.
• Winter Solstice, December 21, is the day when the North Pole is most tilted away from the Sun.
• The tilt is also responsible for the different seasons that we see on Earth.
• The side facing the Sun experiences day, which changes to night as Earth continues to spin on its axis.

Un-impacted regions

• On the Equator, day and night are equal. The closer one moves towards the poles, the more extreme the variation.
• During summer in either hemisphere, that pole is tilted towards the Sun and the polar region receives 24 hours of daylight for months.
• Likewise, during winter, the region is in total darkness for months.

Celebrations associated with the Winter Solstice

• For centuries, this day has had a special place in several communities due to its astronomical significance and is celebrated in many ways across the world.
• Jewish people call the Winter Solstice ‘Tekufat Tevet’, which marks the start of winter.
• Ancient Egyptians celebrated the birth of Horus, the son of Isis (divine mother goddess) for 12 days during mid-winter.
• In China, the day is celebrated by families coming together for a special meal.
• In the Persian region, it is celebrated as Yalda or Shab-e-Yalda. The festival marks the last day of the Persian month of Azar and is seen as the victory of light over darkness.
• Families celebrate Yalda late into the night with special foods such as ajeel nuts, pomegranates and watermelon, and recite works of the 14th century Sufi poet Hafiz Shirazi.

In Vedic tradition

• In Vedic tradition, the northern movement of the Earth on the celestial sphere is implicitly acknowledged in the Surya Siddhanta.
• It outlines the Uttarayana (the period between Makar Sankranti and Karka Sankranti). Hence, Winter Solstice is the first day of Uttarayana.

China and Nepal have announced Mount Everest is 0.86 m taller than the 8,848 m accepted globally so far.

Try this PYQ:

Q.When you travel to the Himalayas, you will see the following:

1. Deep gorges
2. U-turn river courses
3. Parallel mountain ranges
4. Steep gradients causing land-sliding

Which of the above can be said to be the evidences for the Himalayas being young fold mountains?

(a) 1 and 2 only

(b) 1, 2 and 4 only

(c) 3 and 4 only

(d) 1, 2, 3 and 4

Scaling a mountains’ height

• The basic principle that was used earlier is very simple and uses  only trigonometry which most of us are familiar with, or at least can recall.
• There are three sides and three angles in any triangle. If we know any three of these quantities, provided one of them is a side, all the others can be calculated.
• In a right-angled triangle, one of the angles is already known, so if we know any other angle and one of the sides, the others can be found out.
• This principle can be applied for measuring the height of any object that does not offer the convenience of dropping a measuring tape from top to bottom.

Accuracy issues

• For small hills and mountains, whose top can be observed from relatively close distances, this can give quite precise measurements.
• But for Mount Everest and other high mountains, there are some other complications.
• These again arise from the fact that we do not know where the base of the mountain is.

Measuring against sea level

• Generally, for practical purposes, the heights are measured above mean sea level (MSL). Moreover, we need to find the distance to the mountain.
• This is done through a painstaking process called high-precision levelling. Starting from the coastline, we calculate step by step the difference in height, using special instruments.
• This is how we know the height of any city from mean sea level.

Adjusting gravitation anomaly

• But there is one additional problem to be contended with — gravity. Gravity is different in different places. It means that even sea level cannot be considered to be uniform at all places.
• So, the local gravity is also measured to calculate the local sea level. Nowadays sophisticated portable gravitometers are available that can be carried even to mountain peaks.

Technology solutions

• These days GPS is widely used to determine coordinates and heights, even of mountains.
• But, GPS gives precise coordinates of the top of a mountain relative to an ellipsoid which is an imaginary surface mathematically modelled to represent Earth.
• This surface differs from the mean sea level. Similarly, overhead flying planes equipped with laser beams (LiDAR) can also be used to get the coordinates.

How accurate are China/Nepal’s apprehensions?

• Considering that during 1952-1954, when neither GPS and satellite techniques were available nor the sophisticated gravimeters, the task of determining the height of Mount Everest was not easy.
• Nepal and China have said they have measured Mount Everest to be 86 cm higher than the 8,848 m that it was known to be.
• But these have been explained in terms of geological processes that might be altering the height of Everest. The accuracy of the 1954 result has never been questioned.
• Most scientists now believe that the height of Mount Everest is increasing at a very slow rate. This is because of the northward movement of the Indian tectonic plate that is pushing the surface up.
• Big earthquake, like the one that happened in Nepal in 2015, can alter the heights of mountains. Such events have happened in the past.