In a major discovery, footprints of three species of dinosaurs have been found in the Thar desert in Rajasthan’s Jaisalmer district, proving the presence of the giant reptiles in the western part of the State, which formed the seashore to the Tethys Ocean during the Mesozoic era.
Prelims, GS-I: Geography (Geomorphology)
Dimensions of the Article:
- Back to the Basics: Understanding the Periods, Epochs, Ages etc.
- Timeline: Eras – Periods – Epochs – Ages
- About the Recent discovery of fossils in Rajasthan
- Other Dinosaur fossils discovered in India
Back to the Basics: Understanding the Periods, Epochs, Ages etc.
- The geologic time scale (GTS) is a system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history.
- The primary and largest catalogued divisions of time are periods called eons.
- The first eon was the Hadean, starting with the formation of the Earth and lasting over 600 million years until the Archean eon, which is when the Earth had cooled enough for continents and the earliest known life to emerge.
- After about 2.5 billion years, oxygen generated by photosynthesizing single-celled organisms began to appear in the atmosphere marking the beginning of the Proterozoic.
- Finally, the Phanerozoic eon encompasses 541 million years of diverse abundance of multicellular life starting with the appearance of hard animal shells in the fossil record and continuing to the present.
- The first three eons (i.e., every eon but the Phanerozoic) can be referred to collectively as the Precambrian supereon. This is about the significance of the Cambrian Explosion, a massive diversification of multi-cellular life forms that took place in the Cambrian period at the start of the Phanerozoic. Eons are divided into eras, which are in turn divided into periods, epochs and ages.
- Corresponding to eons, eras, periods, epochs and ages, the terms “eonothem”, “erathem”, “system”, “series”, “stage” are used to refer to the layers of rock that belong to these stretches of geologic time in Earth’s history.
- Geologists qualify these units as “early”, “mid”, and “late” when referring to time, and “lower”, “middle”, and “upper” when referring to the corresponding rocks. For example, the Lower Jurassic Series in chronostratigraphy corresponds to the Early Jurassic Epoch in geochronology.
- The adjectives are capitalized when the subdivision is formally recognized, and lower case when not; thus “early Miocene” but “Early Jurassic.”
Timeline: Eras – Periods – Epochs – Ages
- The fossil records show that something unusual happened millions of years ago. A wide range of animals from terrestrial megafauna to tiny aquatic beings died suddenly. This extinction of a large number of animals altogether is known as a mass extinction.
- As the new species start evolving, the old species got depleted from the earth. More than 90% of the species are believed to have become extinct in the last 500 million years.
There are six periods in the Paleozoic era: Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.
- Spans from 541 to 485 million years ago.
- The Cambrian sparked a rapid expansion in evolution in an event known as the Cambrian Explosion during which the greatest number of creatures evolved in a single period in the history of Earth.
- Plants like algae evolved, and arthropods dominated the fauna.
- Almost all marine phyla evolved in this period.
- Spans from 485 million years to 440 million years ago.
- Many species still prevalent today evolved, such as primitive fish, corals, etc.
- The most common forms of life, however, were trilobites, snails and shellfish.
- More importantly, the first arthropods crept ashore (the beginning of terrestrial lifeforms).
- By the end of the Ordovician, Gondwana had moved from the equator to the South Pole.
- The glaciation of Gondwana resulted in a major drop in sea level, killing off all life along its coast.
- Glaciation caused a snowball Earth, leading to the Ordovician-Silurian extinction (First Mass Extinction).
Ordovician–Silurian extinction (First Mass Extinction)
- This is considered as the second deadliest in the history of Earth.
- This event greatly affected marine communities.
- As the southern supercontinent, Gondwana drifted over the South Pole, ice caps formed on it.
- A combination of lowering of sea level and glacially driven cooling were likely driving agents.
- A fall in atmospheric carbon dioxide preceded the late Ordovician glaciation event.
- The dip is correlated with a burst of volcanic activity that deposited new silicate rocks, which draw CO2 out of the air as they erode.
- The Silurian spans from 440 million years to 415 million years ago.
- It saw warming from Snowball Earth.
- This period saw the mass evolution of fish.
- The first freshwater fish evolved, though arthropods, such as sea scorpions, remained the apex predators.
- Fully terrestrial life evolved, which included fungi, and centipedes.
- The evolution of vascular plants allowed plants to gain a foothold on land.
- During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, India), Laurentia (North America with parts of Europe), Baltica (the rest of Europe), and Siberia (Northern Asia).
- The recent rise in sea levels provided new habitats for many new species.
- Spans from 415 million years to 360 million years ago.
- Also known as the Age of the Fish, the Devonian features a huge diversification in fish.
- On land, plant groups diversified; the first trees and seeds evolved.
- By the Middle Devonian, shrub-like forests of primitive plants existed.
- This event allowed the diversification of arthropod life as they took advantage of the new habitat.
- The first amphibians also evolved, and the fish were now at the top of the food chain.
- Near the end of the Devonian, 70% of all species became extinct in an event known as the Late Devonian extinction, which is the second mass extinction known to have happened.
Late Devonian extinction (Second Mass Extinction)
- The Late Devonian extinction occurred about 376–360 million years ago.
- The extinction seems to have only affected marine life.
- The causes of these extinctions are unclear.
- Leading hypotheses include changes in sea level and ocean anoxia (lack of oxygen), possibly triggered by global cooling or oceanic volcanism.
- Spans from 360 million to 300 million years ago.
- Tropical swamps dominated the Earth, and the large amounts of trees created much of the carbon that became coal deposits (hence the name Carboniferous).
- The high oxygen levels caused by these swamps allowed massive arthropods, normally limited in size by their respiratory systems, to proliferate.
- Perhaps the most important evolutionary development of the time was the evolution of amniotic eggs, which allowed amphibians to move farther inland. (Amniotic fluid is a clear, slightly yellowish liquid that surrounds the foetus).
- Also, the first reptiles evolved in the swamps.
- Throughout the Carboniferous, there was a cooling pattern, which eventually led to the glaciation of Gondwana as much of it was situated around the south pole.
- Spans from 300 million to 250 million years ago.
- At its beginning, all continents came together to form the super-continent Pangaea, surrounded by one ocean called Panthalassa.
- The Earth was very dry during this time, with harsh seasons, as large bodies of water didn’t regulate the climate of the interior of Pangaea.
- Reptiles flourished in the new dry climate.
- Creatures such as Dimetrodon and Edaphosaurus ruled the new continent.
- The first conifers evolved, then dominated the terrestrial landscape.
- Nearing the end of the period, Scutosaurus and gorgonopsids filled the arid landmass.
- Eventually, they disappeared, along with 95% of all life on Earth in an event simply known as “the Great Dying“, the world’s third mass extinction event and the largest in its history.
Permian–Triassic extinction event (Third Mass Extinction)
- The Permian–Triassic (P-T) extinction event is also known as the Great Dying.
- It occurred about 252 Ma (million years) ago, forming the boundary between the Paleozoic and the Mesozoic eras.
- It is the Earth’s most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct.
- It is the only known mass extinction of insects.
- Suggested causes include large meteor impact events, massive volcanism such as that of the Siberian Traps, runaway greenhouse effect triggered by the sudden release of methane from the sea floor due to methane-producing microbes known as methanogens.
- Possible contributing gradual changes include sea-level change, increasing anoxia, increasing aridity, and a shift in ocean circulation driven by climate change.
- Spans from 250 million to 66 million years ago.
- Also known as “the Age of the dinosaurs“, the Mesozoic features the rise of reptiles.
- There are three periods in the Mesozoic: Triassic, Jurassic, and Cretaceous.
- Triassic Period: Spans from 250 million to 200 million years ago. It is a transitional time between the Permian Extinction and the lush Jurassic Period. It has three major epochs: Early Triassic, Middle Triassic and Late Triassic.
- Jurassic Period: Spans from 200 million to 145 million years ago, and features three major epochs: Early Jurassic, Middle Jurassic, and Late Jurassic.
- Cretaceous Period: Spans from 145 million to 66 million years ago, and is divided into two epochs: Early Cretaceous, and Late Cretaceous.
Triassic–Jurassic extinction event (Fourth Mass Extinction)
- It marks the boundary between the Triassic and Jurassic periods, 201 million years ago.
- This event happened in less than 10,000 years and occurred just before Pangaea started to break apart.
- On land, all archosaurs except a few and many of the large amphibians became extinct.
- This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant role.
- Gradual climate change, sea-level fluctuations, oceanic acidification reached a tipping point.
- Massive volcanic eruptions might have caused intense global warming (release of carbon dioxide or sulphur dioxide) or intense global warming (release of aerosols).
Cretaceous–Paleogene extinction event (Fifth Extinction)
- The Cretaceous-Paleogene (K-Pg) or Cretaceous-Tertiary (K-T) extinction, was a sudden mass extinction on Earth approximately 66 million years ago.
- At the end of the Cretaceous, the Deccan Traps and other volcanic eruptions were poisoning the atmosphere.
- As this was continued, it is thought that a large meteor smashed into Earth, creating the Chicxulub Crater (Yucatan Peninsula Mexico) creating the event known as the K-T Extinction.
- Every living thing with a body mass over 10 kilograms became extinct, and the age of the dinosaurs came to an end.
- In its wake, many groups underwent remarkable adaptive radiation—sudden and prolific divergence into new forms and species.
- Mammals in particular diversified in the Paleogene, evolving new forms such as horses, whales, bats, and primates. Birds, fish, and perhaps lizards also radiated.
- The Cenozoic featured the rise of mammals as the dominant class of animals.
- There are three divisions of the Cenozoic: Paleogene, Neogene and Quaternary.
- Paleogene Period: Spans from the extinction of the non-avian dinosaurs, some 66 million years ago, to the dawn of the Neogene 23 million years ago. It features three epochs: Paleocene, Eocene and Oligocene.
- Neogene Period: Spans from 23.03 million to 2.58 million years ago.
- It features 2 epochs: the Miocene, and the Pliocene.
- Spans from 2.58 million years ago to the present day.
- It features modern animals and dramatic changes in the climate.
- It is divided into two epochs: the Pleistocene and the Holocene.
About the Recent discovery of fossils in Rajasthan
- Footprints of three species of dinosaurs have been found in the Thar desert in Rajasthan – the three species of dinosaurs are — Eubrontes cf. giganteus, Eubrontes glenrosensis and Grallator tenuis.
- The dinosaur species are considered to be of the theropod type, with the distinguishing features of hollow bones and feet with three digits. All the three species, belonging to the early Jurassic period.
Other Dinosaur fossils discovered in India
- The first dinosaur bones in Asia were found in India by a British captain in one of the East India Co.’s armies in 1828, in Jabalpur, thirteen years before the word “dinosaur” was coined. Ever since then many bones, nests, and eggs have been found across the country.
- In 1981, geologists stumbled upon thousands of fossilized dinosaur eggs in Balasinor, Gujarat. Paleontologists believe that at least seven species of dinosaur lived here – perhaps the most famous being the squat, two-legged, carnivorous Rajasaurus narmadensis
- In 2017, the fossil bones of a Shringasaurus, a horned, herbivorous dinosaur, were discovered in red mudstone of the Denwa formation, in Madhya Pradesh.
- A team of scientists from the Geological Survey of India have discovered fossil evidence of sauropod dinosaurs dating back 100 million years (final conclusion is yet to be drawn by GSI) from the West Khasi Hills in Meghalaya in May 2021. (Dinosaur bones from Meghalaya were reported by GSI in 2001 but they were too fragmentary and ill-preserved to understand its taxonomic identification).
-Source: The Hindu