This is the 12285th most frequent Russian word.
исследовалась
"Was being researched"
The word 'исследовалась' is used in the past passive voice to indicate that the subject (the topic) was being studied by someone (scientists).
Эта тема исследовалась многими учёными на протяжении десятилетий.
This topic has been studied by many scientists over the decades.
Here, 'исследовалась' is part of a subordinate clause, communicating a specific focus area that was studied.
Область биологии, в которой исследовалась эта мутация, расширяется с каждым годом.
The field of biology in which this mutation was studied expands every year.
In this example, 'исследовалась' describes the subject of exploration, indicating what specific aspect was studied during the expedition.