Abstract
The Atacama Desert is by far the driest and oldest desert on Earth, showing a unique combination of environmental extremes (extreme dryness, the highest UV radiation levels on Earth, and highly saline and oxidizing soils), explaining why the Atacama has been largely investigated as a Mars analog model for almost 20 years. Based on the source and the amount of water available for life and its analogy with Mars, two ecosystems are of interest in the Atacama: its Coastal Range and the much drier hyperarid core, which we here review in detail. Members of the three domains of life have been found across these ecosystems living at the limit of habitability, suggesting the potential dry limits for each domain and also unveiling the highly patchy distribution of microbial life in its most extreme regions. The thorough study of the Atacama has allowed us to understand how life has adapted to its extreme conditions, the specific habitats that life occupies in each case (thus suggesting the most likely places in which to search for evidence for life on Mars), and the number of biosignatures detected across this desert. Also, the characterization of west-to-east transects across this desert has shown to be of significant value to understand the potential adaptations that Martian microorganisms may have followed in an ever-drying planet. All of this explains why the Atacama is actively used as the testing ground of the technologies (detection instruments, rovers, etc.) that were sent and will be sent to Mars. We also highlight the need to better inform the exact locations of the sites studied to understand general trends, the need to identify the true native microbial species of the Atacama, and the impact of climate change on the most arid and most Martian desert of Earth.
Highlights
The Atacama Desert is located in northern Chile, framed by the Andes Mountains on the east and by the Pacific Ocean on the west (Figures 1A,B)
The extreme aridity of the Atacama is explained by three main factors (Figure 2); its location within the southern hemisphere dry subtropical climate belt, the pronounced rain shadow effect of the Andean Mountains that prevent the incoming of humid masses of air coming from the Amazon Basin, and the presence of the upwelling, north-flowing, cold Humboldt Current, which significantly reduces sea water evaporation and cloud formation (Somoza and Tomlinson, 2002; Houston and Hartley, 2003; Hartley et al, 2005; Azua-Bustos et al, 2015)
To aid the organization of the findings covered in this review, we summarize them into two main ecosystems from the point of view of the analogy with Mars (Figure 1C); the Coastal Range and the hyperarid core, a selection based on the source and critically, the amount of water available for life in each region
Summary
The Atacama Desert is located in northern Chile, framed by the Andes Mountains on the east and by the Pacific Ocean on the west (Figures 1A,B). The Atacama is known for having the highest UV radiation on Earth, with annual UVB doses ranging from 3.5 to 5 kWh/m2 on the Coastal Range of the Atacama and UVA doses ranging from 130 to 160 kWh/m2 on the Andes Mountains (Cordero et al, 2018). This assemblage of extreme environmental conditions explains why since 2003, many reports have described the meteorological, geophysical, and microbiological characteristics of the Atacama in order to study it as a Mars analog model (AzuaBustos et al, 2012). To aid the organization of the findings covered in this review, we summarize them into two main ecosystems from the point of view of the analogy with Mars (Figure 1C); the Coastal Range and the hyperarid core, a selection based on the source and critically, the amount of water available for life in each region
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