Scientists estimate that our Solar System is 4.567 billion years old. But, have you ever wondered how it was formed? How did the planets take shape from the initial gas and dust of the solar nebula and eventually, how did life evolve on Earth? What processes shaped the initial evolution of our Solar System? These fundamental questions drive Prof. Ramananda Chakrabarti and the researchers in his lab at the Center for Earth Sciences, Indian Institute of Science, Bangalore, to study rocks on Earth and from space.
Members of Prof. Chakrabarti’s lab use geochemical and isotopic compositions of such rocks to reconstruct the early history of the Solar System as well as the Earth. Some of the isotopic variability in these samples is caused by radioactivity, a process where unstable atoms of some elements having extra neutrons in the nucleus undergo “decay” to become stable. They lose particles from the nucleus, the center of the atom, in the process. The resulting atom might be of the same element or of a different element. The amount of time taken for the parent atom to decay to half of its initial amount is called the “half-life” which can vary from a few seconds to billions of years. Variations in the relative concentrations of “parent” and “daughter” atoms (expressed as ratios) are used to infer the age or time of formation of a rock sample. Such analysis requires a great deal of expertise in chemistry, a very clean laboratory for processing the samples, and a range of modern, state-of-the-art instruments called mass spectrometers which Prof. Chakrabarti’s lab boasts of.
“Imprints of early Solar System processes are preserved in space rocks called meteorites, which are remnants of planetary bodies that were destroyed due to planetary collisions”, explains Prof. Chakrabarti. These rocks have crashed on the surface of the Earth and are some of the oldest objects found on earth. Some meteorites that haven't changed chemically since their accretion from the solar nebula are called chondrites. These meteorites also contain pre-solar grains like Silicon Carbide, which is a product of supernovae events (collapse of stars), which happened even before our Solar System was born. One such chondrite called Allende that crashed in Mexico about 40 years ago is the most studied meteorite. Several meteorites have fallen in India including a very famous Martian meteorite called Shergotty. Isotopic studies of ordinary chondrite samples in Prof. Chakrabarti’s lab have captured planetary collision induced-volatilization events in the parent bodies of these chondrites.
Planetary collisions were very common in the early Solar System as evidenced from the ubiquitous presence of impact craters in different planetary bodies in our Solar System including the Earth. One such meteorite-impact crater, which Prof. Chakrabarti’s lab has been studying, is the Lonar crater in central Maharashtra. The Lonar crater is a rare terrestrial crater hosted on basalts and is an analog for craters in the objects of the inner Solar System. The crater is now filled with water and is one of the largest saltwater lakes in India. When the meteoritic impactor hit the Earth's surface, it caused momentary melting as well as vaporization followed by re-solidification of the melt. The impactor vaporized completely upon impact, but its geochemical and isotopic signature is preserved in micron-sized melt droplets called ‘spherules’ that were carefully separated from the soil samples collected around the Lonar crater and analyzed using laser ablation mass spectrometry. “Our geochemical and isotopic analysis of the melt rocks and spherules from Lonar show evidence for mixing with a chondritic meteoritic impactor as well as melting of old granitic crust beneath the Deccan basalts. These results have implications for future sample return missions from Mars or other asteroids”, adds Prof. Chakrabarti.
Apart from studying the early Solar System processes, Prof. Chakrabarti is also interested in understanding the evolution of surface conditions on early Earth by studying chemical sediments that formed out of ancient seawater. Given that the seawater at any time is in chemical equilibrium with the atmosphere of that time, information on the evolution of paleo-climatic conditions on the surface of the Earth is imprinted in the compositions of such rocks. Understanding the evolution of climatic conditions on early Earth is critical to studying the origin and evolution of life of Earth. Overall, Dr. Chakrabarti’s lab uses geochemical and isotopic proxies to understand wide-ranging processes from the “Cosmos to Benthos”.