Mass Extinctions in the history of Life: Significance of NASA’s Artemis Moon and Planetary Defence DART Missions
Evolution and extinction of new species have gone hand in hand since life began on Earth. However, there have been at least five episodes of large-scale extinctions of life-forms in the past 500 million years. In these episodes, more than three-quarters of the existing species got eliminated. These are referred to as global extinction or mass extinction. The Fifth Mass Extinction was the last such episode that occurred about 65 million years ago in Cretaceous period. This was caused due to asteroid impact. The resulting conditions led to the elimination of dinosaurs from the face of Earth. In the current Anthropocene period (i.e., the period of humanity), it is suspected that the Earth may already be in or on the verge of Sixth Mass Extinction, due to man-made environmental issues (such as climate change, pollution, deforestation, global warming, etc.). Further factors like nuclear, biological or other types of warfare/conflict, natural environmental disasters such as volcanic eruption or asteroid impact also have the potential to trigger mass extinction. Spreading out into space is one of the ways to deal with existential challenges posed. NASA’s Artemis Moon Mission is a beginning towards deep space human habitation by future colonisation of the Moon and Mars. Planetary defence by deflecting an asteroid away from the Earth is another strategy being considered. NASA’s DART Mission is the first such asteroid deflection test. This mission will try to deflect a near-Earth asteroid next month.
The environment has always been changing all the time. This had a two-pronged effect on the life forms — while negative selection pressure against those unfit to survive in the environment lead to their extinction, on the other hand, it favoured survival of the life forms flexible enough to adapt to new conditions. This eventually resulted in the culmination of evolution of new species. Hence, extinction and evolution of new life forms should have gone hand in hand, almost seamlessly since the beginning of life on the Earth.
However, the history of Earth has not always been smooth. There were instances of dramatic and drastic events which had strong adverse impact on life forms resulting in very large-scale extinction of species. ‘Global extinction’ or ‘mass extinction’ is the term used to describe episodes when about three-quarters of the existing biodiversity became extinct in a relatively short interval of geologic time. In the last 500 million years, there were at least five instances of large-scale mass extinction1.
Table: Earth, Mass Extinctions of Species and Humanity
Time before present (in years) Events 13.8 billion years ago Universe began Time, space and matter all began with the Big Bang 9 billion years ago Solar system formed 4.5 billion years ago Earth formed 3.5 billion years ago Life began 2.4 billion years ago Cyanobacteria evolved 800 million years ago First animal (sponges) evolved 541–485 million years ago (Cambrian period) Wild explosion of new life forms 400 million years ago (Ordovician — Silurian period) First mass extinction called the Ordovician-Silurian Extinction 365 million years ago (Devonian period) Second mass extinction called Devonian extinction 250 million years ago. (Permian-Triassic period) Third mass extinction called Permian-Triassic extinction, or the Great Dying more than 90 percent of the Earth’s species became extinct 210 million years ago (Triassic- Jurassic periods) Fourth mass extinction eliminated many large animals cleared the way for dinosaurs to flourish earliest mammals evolved around this time 65.5 million years ago (Cretaceous period) Fifth mass extinction called end-Cretaceous extinction caused due to asteroid impact brought the age of the dinosaurs to an end 55 million years ago First primates evolved 315,000 years ago Homo sapiens evolved in Africa Present Anthropocene period (i.e., the period of humanity) Sixth mass extinction (?) Experts suspects that the Earth may already be in or on the verge of mass extinction due to man-made environmental issues (such as climate change, pollution, deforestation, global warming, etc.) Further, following factors have the potential to cause mass extinctions conflicts culminating in nuclear/biological wars/disasters environmental disasters such as massive volcanic eruption impact with an asteroid
This ‘Big Five’ extinctions were described based on analysis of a database about thousands of marine invertebrate fossils.
In the Cambrian period (541–485 million years ago), there was a wild explosion of new life forms. This was followed by the First Mass Extinction of life on Earth that took place 400 million years ago in Ordovician — Silurian period. This saw extinction of more than 85% of marine biodiversity resulting from climate change due to global cooling of tropical ocean followed by reduction in sea level and loss of habitats in low lying areas. The Second Mass Extinction occurred 365 million years ago in the Devonian period which seems to be caused due to reduction in oxygen concentration of water when the sea level was high. Volcanic activity is currently thought of as the causative factor behind the second extinction1.
The Third Mass Extinction or Permian-Triassic extinction happened about 250 million years ago in Permian-Triassic period. This is also called Great Dying because more than 90 percent of the Earth’s species were eliminated. This was caused due to drastic climate change following rapid global warming as a result of massive release of greenhouse gases especially the six-fold increase of CO2 in the atmosphere1,2. This also explains causation of the fourth mass extinction or Triassic-Jurassic extinction 210 million years ago which saw elimination of many large animals clearing the way for dinosaurs to flourish. Massive volcanic eruptions seem to be the event associated with these two great extinctions.
The most recent, end-Cretaceous extinction (or Cretaceous-Paleogene extinction or the Fifth Mass Extinction) occurred about 65.5 million years ago. This was one of the largest mass extinctions in the history of life that saw complete elimination of all non-avian dinosaurs. There were both avian and non-avian dinosaurs. Avian dinosaurs were warm-blooded while non-avian dinosaurs were cold-blooded. Flying reptiles and non-avian dinosaurs suffered total extinction while the phylogenetic descendants of avian dinosaurs survive to the modern day, marking the abrupt end of the age of the dinosaurs. That was the time when massive changes in the environment were taking place due to impact of a large asteroid with the Earth at Chicxulub, Mexico and duo to vast volcanic eruptions that culminated in climate change causing drying up of supporting food supply. Asteroid impact not only caused shock-waves, a large heat pulse and tsunamis, but also released huge amount of dust and debris in the atmosphere that stopped sunlight to reach the Earth’s surface hence near cessation of photosynthesis and a prolonged winter. The lack of photosynthesis meant destruction of primary producer plants including phytoplankton and algae as well as of dependent animal species1,3. Asteroid impact was the main driver of extinction but volcanic eruptions around the time, on the one hand, contributed in mass extinction by further worsening darkness and winter by throwing plumes of smoke and dust in the atmosphere. On the other hand, it also induced warming from volcanism4. As for the total extinction of the entire family of non-avian dinosaurs, the study of physiology of descendants of avian dinosaurs suggests that there was failure to reproduce due to deficiency of vitamin D3 (cholecalciferol) in the developing embryos in eggs leading to death before hatching5.
In the present Anthropocene period (i.e., the period of humanity), some researchers argue that a Sixth Mass Extinction is already currently underway courtesy of man-made environmental issues such as climate change, pollution, deforestation, global warming, etc. This is based on estimates of current extinction rates of species, which are found to be in similar range to species extinction rates for earlier mass extinctions1. In fact, results from another study confirm that current rates of extinction of biodiversity are far higher than the extinction rates for the five earlier mass extinctions obtained from the fossil record 6,7,8 and the conservation initiatives do not seem to be helping much8. Furthermore, there are other man-made factors like nuclear war/disaster that have the potential to trigger mass extinction. Global collective steps and consistent efforts towards disarmaments, mitigation of climate change, carbon emission reduction and species conservation notwithstanding, some researchers suggest to reduce the scale of the human enterprise, shrinkage of human population by further reduction of birth rates and the end of ‘growth mania’9.
Like the last end-Cretaceous extinction, any future environmental disaster arising from possible impacts from space and/or from massive volcanic eruptions may also pose serious existential challenge before mankind because in the long run, like every planet, Earth will be endangered by impacts from space (as well as by volcanic eruptions) culminating in cessation of photosynthesis due to prolonged darkness hence all primary producer plants and dependent animal species will face decimation.
Colonisation of deep space and deflecting earth-bound asteroids away from the Earth are two possible responses of mankind to the existential threats posed by impacts from space. NASA’s Artemis Moon Mission is a beginning towards deep space human habitation for making humans a multi-planet species. This programme will not only create long-term human presence on and around the Moon but also teach lessons in preparation for human missions and habitations on Mars. Artemis mission will build a base camp on the lunar surface to give astronauts a home to live and work on the Moon. This will be the first instance of humans living on the surface of another celestial body10. NASA’s planetary defence DART Mission is set to test a method of deflecting an asteroid away from the Earth. Both of these space missions hold considerable promise towards mitigation of existential challenges to mankind posed by impact from space.
- Khlebodarova TM and Likhoshvai VA 2020. Causes of global extinctions in the history of life: facts and hypotheses. Vavilovskii Zhurnal Genet Selektsii. 2020 Jul;24(4):407–419. DOI: https://doi.org/10.18699/VJ20.633 | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7716527/
- Wu, Y., Chu, D., Tong, J. et al. Six-fold increase of atmospheric pCO2 during the Permian–Triassic mass extinction. Nat Commun 12, 2137 (2021). https://doi.org/10.1038/s41467-021-22298-7
- Schulte P., et al 2010. The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary. SCIENCE. 5 Mar 2010. Vol 327, Issue 5970. DOI: https://doi.org/10.1126/science.1177265
- Chiarenza AA et al 2020. Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction. Published June 29, 2020. PNAS. 117 (29) 17084–17093. DOI: https://doi.org/10.1073/pnas.2006087117
- Fraser, D. (2019). Why did the dinosaurs become extinct? Could cholecalciferol (vitamin D3) deficiency be the answer? Journal of Nutritional Science, 8, E9. DOI: https://doi.org/10.1017/jns.2019.7
- Barnosky A.D., et al 2011. Has the Earth’s sixth mass extinction already arrived? Nature. 2011;471(7336):51–57. DOI: https://doi.org/10.1038/nature09678
- Ceballos G., et al 2015. Accelerated modern human-induced species losses: Entering the sixth mass extinction. Sci. Adv. 2015;1(5): e1400253. DOI: https://doi.org/10.1126/sciadv.1400253
- Cowie RH et al 2022. The Sixth Mass Extinction: fact, fiction or speculation? Biological Reviews. Volume 97, Issue 2 April 2022 Pages 640–663. First published: 10 January 2022. DOI: https://doi.org/10.1111/brv.12816
- Rodolfo D., Gerardo C., and Ehrlich P., 2022. Circling the drain: the extinction crisis and the future of humanity. Published:27 June 2022. Philosophical Transactions of The Royal Society Biological Sciences. B3772021037820210378 DOI: http://doi.org/10.1098/rstb.2021.0378
- Prasad U., 2022. Artemis Moon Mission: Towards Deep Space Human Habitation. Scientific European. Published 11 August 2022. Available at https://www.scientificeuropean.co.uk/sciences/space/artemis-moon-mission-towards-deep-space-human-habitation/